Dip hopping originated in Japan but is becoming increasingly popular in North America. Learn more how to use this technique in your Nano brewery to boost pleasant hop aromas while suppressing or removing unpleasant off-flavors, like myrcene, and aromas that are derived from fermentation.

PDF of Presentation Slides: https://byo.com/wp-content/uploads/Ashton_Lewis_Nanocon_2025_Dip-Hopping-2.pdf

Like many avid homebrewers, I soon found myself growing hops as a hobby that sprung from the joys of homebrewing beer. I got Cascade rhizomes from a coworker at a brewery I was working at and once planted they really took off.

I planted the hop rhizomes at the base of my grandmother’s blue spruce tree to allow the tree to become my trellis for the hops to grow on using minimal effort. By the third year I had a sufficient hop harvest to brew a 5-gallon (19-L) batch of my roasted sweet potato pale ale using fresh Cascade hops that I grew.

As the years went on the hop plant produced an abundance of hops to brew with and I was soon making several fresh-hop (or wet-hop) recipes that utilized the hops shortly after picking and forgoing the drying process hops generally go through. When brewing with fresh hops you need more weight to account for the water in the hop cones as opposed to the normal dried hops (whether as cones or pellets) that are often below 10% moisture content. I like using a factor of 6 and feel that really lines up with IBU calculations if the hops are added during the boil. This means a lot of fresh hops are needed to brew hoppier beers like pale ales and IPAs.

While drinking a homebrew and watching my hopback/whirlpool during its resting phase on a fresh-hop brew day, I pondered over what the actual utilization was given the large amount of hops that were used, relatively short contact time of 20 to 40 minutes depending on the recipe, and as the wort approached or fell below the isomerization temperature of 176 °F (80 °C). I was thinking of utilization not just with the alpha acids and bitterness, but how much hop oils and terpenes were left in the hops for flavor and character. With these questions and plenty of spent hops in hand, it was time to brew an experimental spent-hopped beer!

Recipe Idea

I assumed that the character of the spent hops would be delicate and would lend itself well to a lighter style hoppy beer. The first style to come to mind was an English bitter. Special bitters are known for lower alcohol content around 3.8–4.6%, with 4% being a great middle target. Special bitters and higher gravity strong bitters (4.6–6.2% ABV) use lower alpha acid hops like East Kent Goldings, which are rich in oils that pack a beer with hop flavor, aroma, with a clean bitterness. This was my inspiration for this project. While hoppy beers are usually the topic when it comes to brewing with fresh hops, don’t be afraid to try using spent fresh hops in other styles. I can imagine doing so in future batches with something like my favorite helles or Pilsner recipe.

Method of Brewing with Fresh Spent Hop Cones

When using wet hops that are freshly picked off the hop bine, the majority of brewers — whether homebrewer or professional — choose the easiest option to add the whole leaf hop cones to the mash tun to act as a hopback or whirlpool. This makes for easy cleanup and you can use a ridiculous amount of hops to extract a unique hop character. Also, by using your mash tun you can easily maximize wort recovery to your fermenter by using the false bottom to aid with wort drainage.

Over the years I guessed my original alpha acids of my homegrown Cascade hops to be about 6% (this is anecdotal based on about 20 years of experience brewing on a home and professional scale) and assumed only 2% alpha acids remaining in the spent hops. I continued to harvest homegrown hops and brew the sweet potato pale ale fresh-hop beer followed by the spent-hop English bitter for five consecutive years. After a few batches of brewing with spent hops I believe this reduced alpha acid percent of about 2% to be correct or close enough without paying for an analysis. 

My current boss at Lindgren Craft Brewery remembered these 5- and 10-gallon (19- and 38-L) homebrew batches that I made every year during hop harvest and once we had our own brewery we decided to give it a try on a commercial 3-barrel scale. The idea was to collect the spent hops in 5-gallon (19-L) buckets to hold for the next batch. That year we brewed two 3-barrel wet-hop IPAs using Newport and Comet varieties, which led to a lot of spent hops to reclaim. Following each wet-hop brew we collected the spent cones in buckets that we sealed and placed in the refrigerator to brew with for a second time the next day.

The following day, the spent hops were added as a whirlpool addition when the wort was below isomerization temperature, around 170 °F (77 °C). After the boil was complete, I immediately transfered the wort from the kettle to the mash tun loaded with spent hop cones and noticed that the temperature went from 212 °F (100 °C) down to 184 °F (84 °C) once everything was in the mash tun. If adding spent hops stored in the refrigerator then you will see a more drastic drop in temperature, so I’d recommend allowing them to come to room temperature first.

Once the spent hops and wort were in the mash tun we used a pump to recirculate the wort and help keep the floating hop cones submerged and moving for maximum interaction between the hops and wort. The goal is to try and remove all the oils from the hop cones and get them suspended in the wort. During recirculation the lupulin will come out of the cone and you will see little yellow balls all throughout the wort, the majority of which make their way to the fermenter. When using spent fresh hops starting at room temperature with a 40-minute whirlpool recirculation we saw the starting temperature around 184 °F (84 °C) and finishing around 170 °F (77 °C). For homebrewing, an occasional stir here and there to help mix the hops and extract the leftover oils into the wort is suggested. Also, with smaller homebrewing equipment you might see faster temperature losses than we did on our commercial equipment, which might dictate how long you can whirlpool the hops in your target temperature range.

Mash Hopping

For some extra fun you can add a portion of your spent hops to the mash, which is said to help release thiols and aid in biotransformation. It is said that you get roughly 20% of the IBUs that you would get during a 60-minute boil from mash hop additions. If you choose, you can build that into your recipe.

Flavor & Character

The hop flavor and character will significantly depend on many factors like hop variety, age of the hop plant, original recipe followed by the spent-hop recipe, amount of hops used, and all other brewing techniques used to produce the beer. As a hop plant grows throughout the years it will become a heartier plant that produces better quality and quantity of alpha acids and hop oils. We have seen this happen at our local commercial hop farm over the last five years. One thing that is constant is the soft, delicate hop character contributed from hops on their second use, which is just delightful. For this particular batch at the brewery, we used spent hops from two fresh-hop IPA batches we brewed just to see what would happen. Because we harvested all of the spent whirlpool hops to use in the next batch we just used that base hop weight prior to brewing and did not account for any wort absorption. Even if measuring out spent hops for a bittering addition, just keep it simple and use the weight as is. We are estimating roughly 2% alpha acids left in the spent hops so there is plenty of room for variance.

When calculating the spent hop weight we used 72 pounds of spent hops (as was written in the previous recipe) in the whirlpool in 110 gallons, or 0.65 lbs. per gallon (78 g/L) of post-boil wort and it had a unique, soft jalapeño pepper character with no heat. This was the first time I experienced this character and attribute it to using more hops than I would normally use, however customers told us they enjoyed the flavor and it sold out quickly. In all subsequent brews I have just used one batch of spent hops into another batch (5.3 oz./gallon or 39 g/L).

Homebrewing vs. Commercial Brewing

A major difference between homebrewing and commercial brewing a wet-hop beer is how you source your hops. If you are commercially brewing on smaller equipment like a barrel or two you might have enough hops if you are growing them yourself, but beyond that you will need to find a commercial source due to the amount needed for your recipe. Another commercial option is to plan the brew ahead with local homebrewers that grow their own to get an estimated expected harvest. With enough participants harvesting various varieties they grow you might be able to acquire enough hops to brew a wet-hop beer, then the spent-hopped beer. For commercial brewing we have been told by our cattle farmer that when we put the spent hops in the grain bins the cows don’t like it and don’t eat it. We were asked to find a way to discard the hops and not add them to the spent mash. Just like with homebrewing, we take the spent hops and add them into empty malt bags to throw out. Everything else on the brewing side is pretty much the same for homebrewers and commercial brewers, just on different size equipment.

Wet Hop Availability and Sources

For brewing with fresh wet hops the best option is to grow your own. I understand that this is not an option for some homebrewers, and it’s rarely an option for commercial breweries. For homebrewing, you can plan to pair up with other local homebrewers that do grow their own hops and see if you can harvest the spent hops from their batch to use in your beer. Some hop suppliers offer fresh hops around harvest season in August-September. You might have to pre-order them, so as soon as they are harvested they can be shipped to you immediately. In today’s world with the internet you have many companies, locations, farms, and hop varieties to choose from for your fresh hop needs.

I am a huge fan of supporting local hop farms. Many states have hop farms that are enthusiastic about their products and love hearing from homebrewers. What is your closest hop farm? Do you have multiple hop farms in your state, or even in a neighboring state? Look up their website and see what they have to offer for varieties and then contact them to check the availability of fresh hops, expected harvest time, pricing, as well as shipping or pickup options.

I have worked at breweries before where we had fresh wet hops shipped in overnight from the Pacific Northwest and while they were excellent products, the less time between harvest and brewing with the wet hops, the better. Homebrewers who grow their own hops have a great advantage here. Luckily for us, GEMS Hop Farm is right down the road from us, which allows us to visit the farm and closely monitor the upcoming harvest schedule as well as participate in harvest. It was the same involvement I had when I was growing the backyard hops myself and brewing with them only hours after harvesting. 

We have noticed that after harvest if you place the hops in the freezer and wait three days to brew you can see up to a 6% loss in weight. I sincerely feel that the moisture that is evaporated in freshly harvested hops will affect the overall character. Not necessarily for the worse, just different.

Spent Fresh Hops vs. Spent T-90 Pellet or Dried Whole Cones

To be honest, I have only ever reused spent hops following a wet-hop brew day; however, I see no reason why this technique should only apply to fresh hops. If you wished to get two turns out of T-90 pellets or whole dried hop cones, you could place the hops in a bag in the kettle on your first brew and reuse the spent hops again for your next batch.

Spent-Hop Recipes

There have been so many ways developed to impart different hop notes in beer. Two of the ways I have explored recently are dip hopping and coolpooling. They are similar in that neither method isomerizes hop alpha acids. Without isomerization, the hops do not impart bittering but can add a great deal of flavor and aroma. 

In this article I will break down how the two processes work, how they are similar and how they are different, and the impacts I have seen from both. My hope is you will be curious enough about the two techniques to try them in your brewing. The reward for those who do will be unique hop expression and increased aroma in your homebrews.

In 2021, when I first learned about dip hopping from an article in Brew Your Own, I was immediately interested in exploring what it had to offer a homebrewer like myself. A newer process that can increase aromatics and open up flavors in hops not normally tasted? How could I not look into it? 

I immediately started a discussion with my brewing partner about the process and in a short time we had our first beers in production using dip hopping techniques. We did a parallel brew of a double IPA and were very impressed with the results. The bittering seemed “softer,” and the hop profiles and aromatics were much more pronounced. We continued our own experiments to make five beers that were dip hopped. This experimentation led to the best double IPAs either of us had ever made. In the last four years I have used this process in over 20 different brews. It’s offered me a way to easily pasteurize the strange herbs and addends I use as a farmhouse brewer while at the same time releasing flavors that I had never encountered before.

The Science Behind Dip Hopping

Dip hopping is a method that helps accentuate pleasant hop aromas while suppressing off-flavors. First developed by brewers at the Kirin Brewery in Japan in 2012, dip hopping involves removing a portion of the wort early in the boil, cooling it, and adding hops to it in a sealed fermenter before fermentation starts. Kirin kept the results of their study very close to the vest for quite some time but revealed some of their results at a brewers’ conference in 2018. The variables they experimented with were temperature, volume of liquid, amounts and types of hop products added, and time of contact.

This technique is believed to produce a few notable effects. The main one is the volatilization of myrcene (β-myrcene), a hop monoterpene that can contribute harsh flavors to beer. Myrcene is a naturally occurring compound found in various plants like hops and cannabis and is known for its grassy, earthy, and sometimes musky aroma. It is one of the key components of hop aroma so it might seem counterintuitive to reduce this hydrocarbon. But by suppressing this component in the liquid and holding it in the wort as a gas, other much more pleasant aroma components are brought to the forefront. Some brewers have reported amplified linalool and geraniol through reduction of myrcene in their own experiments.

One of the most exciting discoveries for me has been the unlocking of new flavors from familiar varieties of hops. Azacca^® and Enigma^® are two hop varieties that typically offer spicy notes. The flavor notes in my own trials were significantly changed in these two varieties of hops through the dip-hop process. Other hops that will benefit from this process are the hop varieties already rich in geraniol or linalool.

Popular geraniol-rich hop varieties:

Cascade
Mosaic^®
Citra^®
Bravo
Amarillo^®
Comet
Pacific Hallertau
Southern Cross
Centennial
Chinook
Motueka
Styrian Golding (Celeia)

Popular linalool-rich hop varieties:

Amarillo^®
Cascade
Columbus
Centennial
Mt. Hood
Nugget
Pacifica
Willamette
Cluster

The dip-hop process can also suppress the production of 2-Mercapto-3-methyl-1-butanol (2M3MB), an off-flavor that can make beer taste onion-like. The suppression of this compound is partly due to lower hydrogen sulfide content in the beer, which is typically associated with the development of off-flavors. There are other things brewers do to reduce the formation of this chemical like controlling oxygen levels during wort preparation, but dip hopping really seems to do the job.

My Experience with Dip Hopping

I have always used boiled wort for my dip-hop additions and have experimented extensively with a contact time of 20–30 minutes with good results. The variables I’ve played with are choice of hops, quantity and types of additions, volume of liquid for steeping, and time in contact. Brewing 5-gallon (19-L) batches, I typically dip hop using 1–2 gallons (4–8 L) of wort (enough to cover the addition with liquid). Keep in mind, pellet hops will absorb liquid and solidify, so be sure to add enough wort to overcome this absorption. I finish the boil and transfer wort at 180 °F (82 °C). At this temperature I am effectively pasteurizing anything that is added to the beer while staying below the temperature where isomerization of the hops occurs. With my system, the dip-hop addition will free fall in temperature to about 150 °F (66 °C) while the remaining wort is cooling. Myrcene volatilizes at 150 °F (66 °C) so this temperature drop works throughout the steeping time. In my studies I have put an airlock on the fermenter to see how long the off-gassing continues, but I now seal the fermenter to hold as much in the way of aromatic compounds as possible in the wort.

I bag what is added to the fermenter, and pull it out prior to transferring the larger volume of cooled wort. I have been successful top cropping yeast if the dip-hop addition is small, (2 oz./56 g or less). But be prepared to lose the ability to harvest yeast if you decide to dip hop. I calculate the IBUs by considering the dip hop as a whirlpool addition. The dip-hop bitterness is softer — very much like a mash-hop addition. This is ideal for hazy IPAs and some less bitter styles, though at times, this soft bitterness has proven to be a bit too soft for my palate and I have adjusted some of my West Coast IPA recipes for a sharper hop note.

Coolpooling

When I started seeing the positive results of dip hopping firsthand, I could not for the life of me understand why more commercial brewers were not doing it. Shortly after starting my journey with dip hopping, Lagunitas made a beer called, “Dip Trip, Free Ride IPA.” In promotional material accompanying the beer at the time, it stated: “The wizard brewers of Lagunitas invented a brand-spankin’-new style of IPA just for IPA Day.” The “brand new” part, which is up for debate, was free rise (no temperature control and dip hopping). After this beer, I heard very little about commercial brewers using the process, but I did hear and see mentions of “coolpooling” from quite a few pro breweries.

Coolpooling is adding hops to cooled wort. Sometimes this addition is in the brew kettle, and other times it is in a secondary vessel. Many commercial brewers do it at 170–180 °F (77–82 °C), but some are known to do it at much cooler temperatures. Some brewers do it in place of whirlpooling in recipes (which consists of adding hops at flameout), and others do both; but either way the goal seems to be the same: Add full hop flavor and aroma without adding bittering.

“We do tend to get better fruit character from the hops with what I’d call a more refined aroma and flavor (through coolpooling),” explains Vinnie Cilurzo, of Russian River Brewing Co. “Bitterness is also lower due to less isomerization, so that needs to be taken into account.”

To learn more about the process of coolpooling, I asked some of the brewers doing it to share how they coolpool with me:

“We get down to about 180–185 °F (82–85 °C) using approximately 10% filtered room temperature water. One of the biggest keys to coolpooling is what temperature water you use. Some brewers will use cold liquor water, which allows you to get a cooler wort by using less diluting water to get to 180–185 °F (82–85 °C).  We are careful to not go below 180 °F (82 °C) as this is the temperature known to keep things sterile.”

– Vinnie Cilurzo, Russian River Brewing

“We don’t add any hops until the coolpool. When we finish our boil (we shorten this to 60 minutes vs. 90 for most of our beers), we run the wort through our counterflow heat exchanger until it reaches 170 °F (77 °C). Then we add a heavy hop addition. We double the contact time we normally use (30 minutes vs. 15 minutes). 

– J. Shilling, Dirt Road Brewing

“I use that technique on a select few of my beers. I pre-chill the entire batch and generally take it to 180–190 °F (82–88 °C) depending on what I am trying to achieve. We begin our 30-minute wort chill about 20 minutes after the whirlpool is complete.”

– John Kimmich, The Alchemist

“I personally haven’t found a big difference in the hop aromatics; we just use whirlpool temperature as a tool for controlling bitterness. Originally, we whirlpool in the kettle, so we’d recirculate through the heat exchanger and back into the kettle to get to the target temperature. Then we’d bypass the heat exchanger and pump for 20 minutes with the hops in there. Then settle for 20 minutes, then run off for ~30 minutes depending on how quickly we could knock-out. We now have a dedicated whirlpool, so we go through a shell and tube heat exchanger onto the hops. Now it’s just the momentum of the transfer that keeps it spinning. Closer to 10 minutes going in, 20-minute rest, 30-minute knockout.”

– Michael Tonsmeire, Sapwood Cellars

Whirlpooling vs. Coolpooling

Whirlpooling hot wort after boiling is used to remove hop material added during the boil. Because the wort is hot enough to isomerize alpha acids, heavy late additions of hops add significant bitterness. When coolpooling, the wort temperature is reduced before the last hot-side hop addition so hop aroma is extracted but alpha acids are not isomerized. Some brewers cool their wort by adding cold water to the kettle and others slightly cool their wort with a wort chiller. With a quicker wort cooling process in coolpooling, brewers are able to preserve terpene compounds and more of the delicate hop flavors and aromas in this hop addition. Rapid cooling also helps prevent the formation of dimethyl sulfide (DMS), a compound that can impart a “cooked vegetable” flavor to beer. In addition to these benefits, the process also aids in settling solids (trub) in the kettle, leading to a clearer beer to transfer out of the fermenter.

With recent products such as Abstrax^® terpene extracts hitting the market, we have more ways to add terpenes to beer later in the process, but if a brewer could avoid the additional expense of these additives, why not? These products still seem like a good thing to have in the brewer’s toolbox to really “dial in” the desired hop flavor profile, but getting a head start helps and many brewers use both to really pack an aromatic punch.

How is Dip Hopping Different Than Coolpooling?

I have found between these two processes that dip hopping suppresses off-flavors while opening up the possibility of accessing new flavors, while coolpooling maintains and enhances more subtle flavors already present in the wort. The big difference in these techniques is that hop solids are removed from wort when coolpooling — as the wort is transferred after a period of coolpooling, leaving the majority behind. Because hop solids remain in the wort/beer when dip hopping, more nucleation sites are added to the fermenting beer. This is why Kirin believes that dip hopping suppresses less desirable “grassy” characteristics of myrcene. Another difference is dip hopping requires sealing the fermenter, ideally preserving more of the aroma compounds.

For commercial brewers, dip hopping can be problematic — which is likely why is isn’t utilized more on the larger scale. Either their systems are not set up to transfer wort to a separate vessel or they lose the ability to harvest yeast due to it, which can be a significant cost factor. Coolpooling seems to be much more easily done on a commercial system. Both methods amplify hop taste and aroma while minimizing bitterness additions, but the science and processes to achieve these results seem very different. Coolpooling is a gentler method for drawing out hop character while preserving subtler flavors that could be overwhelmed by more aggressive methods.

For brewers looking for a harmonious beer, blending the two could help create something more complex with many layers of hop expression, including more subtle flavors that you may have never tasted before. Dip hopping could give that fresh hop hit, while coolpooling could round out the flavors and help integrate them into a more cohesive whole. This approach would definitely require careful consideration of timing and amounts to ensure that the combination isn’t overwhelming, but it’s certainly an interesting avenue to explore.

I see these two processes this way: Dip hopping offers access to new flavors/aromas. Coolpooling gives the brewer a tool to access more subtle flavors/aromas while rounding them out.

My Experience with Coolpooling

In the last few years, I have become focused on the idea of balance in my beers. With IPAs and double IPAs I work with the bitterness units-to-gravity units (BU/GU) ratio as a starting point when designing recipes. A commercial brewer told me he looks at balance using a simple formula of 8–10 IBUs per percentage of alcohol in his finished IPAs. This formula is a quick and easy way to look at the hop balance in my beers, but there is a mathematic formula available to calculate it more precisely. This works with the addition of a “perceived bittering” calculation in addition to the somewhat simpler BU/GU formula. This perceived ratio takes into account the finishing gravity of the beer; sweeter beers do not manifest as bitter on the palate as drier beers do. Neither of these calculators take into account that bittering could be added to the beer with ingredients other than hops, nor do they account for bitterness from hop compounds other than iso-alpha acids.

Since I started looking at this balance ratio, the IBUs in my beers have consistently come down. Some of it is due to a change in my palate, but much of it has to do with the different late-addition processes I now use adding hops to beers. For my test beer I decided to shoot for the low end of the IBU range and see if coolpooling really enhanced the hop expression of flavors and aromatics.

I would commonly design a double IPA recipe like the one to the right with 80 IBUs. However, the Coolpooled IPA calculates to 58, (this results in a BU/GU of 0.725). The IBU range for DIPAs according to the Beer Judge Certification Program (BJCP) is 60–120, so looking at their scale I am at the low end of the range. The final gravity of this beer also did not finish as low as expected, with fermentation stopping at 1.018, which means that it is sweeter than I normally get. I usually hit 1.012–1.014 FG on these styles. If I would have hit these finishing numbers, I would have had an even greater hop punch. I’ll add my reflections on the results following the recipe.

Early-boil hop additions are often called “bitterness additions” as adding bitterness is the primary purpose of this hop charge. That doesn’t mean variety and other factors shouldn’t be considered at this stage. While some brewers may just grab the hops with the highest alpha acid content, others think more critically about the final impact these early hop additions will have. Two pros share how they approach bitterness additions in their beers.

Chris Kirk: Banded Oak Brewing Co.

Chris Kirk co-founded Denver, Colorado’s, Banded Oak Brewing Co. in 2017. In 2025 he partnered with restaurant and bowling alley The Werks to start Paramount Beerwerks in Wheat Ridge, Colorado. 

I like to use Hallertau Magnum as my typical bittering addition hop. I will also often use CTZ or Chinook in my IPAs and double IPAs. However, if I run out of a certain hop variety I would typically use for my bittering addition, I don’t worry too much and will substitute another variety to get me to my goal. Choosing a variety with a similar alpha acid percent is ideal, but a quick calculation can make a hop swap no sweat.

In my experience there will be a slight contribution of hop character that is reflected in the final product from your bittering additions — specifically tannins and phenolic acids. Especially if you’re bittering with a lower alpha acid hop for higher IBU beers. Bittering additions are typically economical decisions for me, but there are a few beers, typically with high protein additions like wheat or oats, that I like to add more hops with lower alpha acids to create a tighter bind in the boil with more polyphenols, resulting in a tight trub cone in the whirlpool and cleaner knockout. 

My bittering additions are typically T-90 pellets. I have used T-45 pellets for bittering additions — the difference is the weight needed to get you to the same IBU. A small bag of hops can go a long way with T-45, but they typically cost more so the economics only make sense if you can find them for a really good price. 

I definitely consider the early additions (75/60 minute boil) my main contributors to my IBU levels. I do attribute some bitterness to the flavor and aroma additions though and will factor that into my recipe development. In order to avoid too much contribution, I will design a heavily hopped beer so that I can use top up water at the end of my boil and pump in cold water to get my boil down fast at flame out and will add my whirlpool additions after the temperature of the wort gets down to around 200 °F (93 °C) to reduce isomerization. 

I was around during the IBU wars of the 2010’s with things like the Alpha King Challenge and tongue numbing bitterness battles that breweries were participating in. I can remember trying beers with upwards of 500 IBUs. Now it’s just the opposite and breweries are trying to create massive dry hopping loads in the juicy and hazy IPAs. While my understanding of bittering has not really changed, my practice and philosophy has changed to meet the market demand. I still prefer to make and offer American and West Coast IPAs, but I have dialed my IBUs way down. My first IPA recipe that I was brewing in 2017 when we opened Banded Oak was 65 IBU and now it’s down to 26 as I’ve moved a majority of those early additions to late-boil  and dry-hop additions. 

My last bit of advice for homebrewers: Watch your pH levels. Alpha acids will have a slower isomerization rate in higher pH worts. And if you’re using hop substitutions, always calculate your weights to stay consistent with different alpha acid percents: 

New weight = old weight x (original AA/new AA). 

Josh Nard: Liquid Mechanics Brewing Co.

Josh Nard is the Head Brewer for Liquid Mechanics Brewing Co. in Lafayette, Colorado.

I have found hop variety decisions related to additions early in the boil are very important. Oil content, alpha acid content, as well as the amount of certain types of alpha acids play a vital role in bitterness quality of the resulting beer. These “bittering” additions can’t be thought of as only for adding bitterness —some hop character definitely makes its way through the boil process from early-boil additions too. I have found the percentage of cohumulone, as well as alpha acid percentage, typically make the biggest impact on the finished beer from this addition. IPAs in particular benefit from the “cleaner,” more refined bitterness of a low-cohumulone hop variety, so I usually use Warrior or Simcoe® for IPAs. For traditional lagers or low-ABV ales, I have found lower alpha acid noble varieties impart a more pleasant bitterness. I usually use Hallertauer Mittelfrüh, Tettnanger, or East Kent Golding T-90 pellets for these types of beers. If I really need more alpha acid, I supplement the noble varieties with Zuper Saazer or German Magnum. 

For IPAs I have switched to some CO₂ extract for bitterness. The extract seems to bring a little less vegetal bitterness than pellets. It also helps lower the quantity of vegetal matter in the kettle, allowing for better yield. Extract can create an oil slick in the kettle, though, so I typically throw some pellets into the boil with the extract to give that oil something to grab onto and incorporate into the liquid better.  

I don’t do my bittering charge until 60 minutes into a 90-minute boil for West Coast IPAs. I get about 50% of the IBUs from that 30-minute addition of extract and pellets. I typically round out the rest with T-90 pellets at 15 minutes or later, and I always do a whirlpool addition. 

Early in my career it was beaten into us that you need a 60-minute addition for IPAs. That later changed to a first wort hop. I did first wort hopping for a very long time, but it seemed the perceivable Bitterness Units (BUs) varied. I still like a first wort hop addition, but I use them rarely, simply for the ease of IBU calculation. Now, I like a 30-minute bittering addition, followed by lots of late additions. They used to call this “hop bursting.” 

The landscape of IPA has changed a lot in the last decade or so. People (me included) seem to enjoy lower IBU IPAs with higher dry hop expression. I’ve learned a lot from brewing New England IPAs. It’s all about perceived bitterness and not particularly the calculated IBUs. Bitterness is one of the five basic tastes, and it’s not a very pleasant one in most cases. Figuring out how to incorporate bitterness into an enjoyable and refreshing experience is really the key. The less you boil, the more character you get from the hops. Just remember, it also means you get less BUs from the hops, which creates more hop load in the kettle, which I make up for with hop extract.

I have done mash hopping and I really enjoy doing it with whole cone hops. Pellets tend to stick up the mash. I usually wait for the sparge and just cover the top of the grain bed with whole cones. We’ve done several collaborations where we use mash hopping to mimic a hop back. I don’t think it makes a huge difference in the flavor of the beer, but we’ll take any opportunity to add even the most subtle hop character. At the very least, it makes the brewery smell amazing!

Let me leave homebrewers with a few pieces of advice. I enjoy the ease of calculating IBUs but it’s not something you should be beholden to. Trust your palate and adjust from there. You may find your IPA tastes best at 30 calculated IBUs rather than 80. You may find your Pilsner tastes better at 40 calculated IBUs rather than 30. 

Don’t be afraid to experiment with all of the new hop products either. Professionals are still figuring out how to incorporate these new products, and homebrewers have a lot of flexibility in how they can experiment with them too. These products are definitely here to stay.

Lastly, make changes incrementally and always experiment. Change one small variable (variety, IBUs, hop product, etc.) and take notes. These small changes will inevitably inform a better product.  

Q: What is the longest you would store hops in the freezer? Would the max storage time be different for bittering vs. aroma hops?
— Ken Grace, via email

A: This question has two very different answers depending on the source of the hops. Let’s start with pelletized hops sold to commercial breweries. These hops begin their journey at the farm, where tall bines are cut from the fields and the cones are separated using a picking machine. Although a small number of farmers now use hop combines that cut, pick, and separate leaves and bines from cones, most still use picking machines housed in buildings typically referred to as picking sheds. Once the picker has disassembled the cones, leaves, and bines, a system of belts and blowers separates out the cones.

The next step is hop kilning, where hot, dry air reduces the moisture content to below 8%. After kilning, the dried hops are stored in large piles to allow the moisture to equilibrate. In most parts of the world, the hops are then compressed into bales. Before pellets became the norm, this was the end of the line for most hops: Bales would be stored in warehouses — often warm ones — before being shipped to breweries. It was U.S. brewers who demanded refrigerated hop storage. In fact, U.S. hop processors routinely store bales in freezers, whereas German processors typically store them in refrigerators at 36–41 °F (2–5 °C).

Because most hops today are pelletized, bales destined for pellet production are usually stored only briefly before being broken apart using a piece of equipment called a bale breaker. The cones are then milled into powder using a hammer mill. The powder is typically blended in a ribbon-style mixer to reduce variability between bales, then compressed into pellets using a forming die. These days, forming dies are cooled with liquid nitrogen and some processors even cool the hop powder prior to forming. Finally, the pellets are packaged in foil bags. The current standard is to flush these bags with nitrogen gas to create a modified atmosphere that reduces oxidation during storage. For many years, vacuum packing was common, but this method makes the bags prone to damage and can cause pellets to clump together into hard-to-handle masses.

The foil bags of hop pellets are then boxed, palletized, transferred to cold storage, and kept there until shipped to breweries or into distribution channels. Depending on the variety — some hops have better storage properties than others — and the intended use, hop pellets can be stored cold for up to six years. In general, pelletized aroma hops start to fade after 2-3 years of storage and bittering hops can hold their brewing value up to about six years. Breweries equipped with lab instruments and trained sensory panels routinely sample and analyze their inventory to determine how best to use it. Because hops are used exclusively in beer, breweries contract with growers to ensure a reliable supply. When aroma hops become unsuitable for brewing, brewers may repurpose them for bittering or take the loss. One major advantage of hop extracts is extended shelf life, which is why many larger breweries convert a portion of their inventory into extracts shortly after pelletizing (most extract facilities are designed to process pellets, which are more compact than cones).

I know I haven’t answered your question yet, but it’s important to understand how pellets are produced and packaged. The issue is this: Pellet bags typically contain 11, 22, or 44 pounds (5, 10, or 20 kg) of hops. Hops sold in the homebrewing market, by contrast, usually come in 1-oz. (28-g) packages. So the obvious question is: How are these 1-oz. (28-g) bags produced?

Typically, they are repackaged from larger bags that are labeled with critical information such as the harvest year, the processor (the company that converts bales into pellets), a lot number, and sometimes a QR code linking to hop analytics. However, not all repackaged pellets retain this vital information. For example, a commercial-sized bag of 2024 Cascade hops labeled with 8.5% alpha, 6% beta, and 1.5% oil might simply become a bag labeled “U.S. Cascade Hops” with a general alpha acid range of 5–9%.

Hops sold to homebrewers are somewhat analogous to growlers or Crowlers^TM of beer. While it is entirely possible to repackage hops without increasing oxygen exposure, the risk is higher. This alone likely shortens the shelf life of homebrew hops compared to those sold to commercial brewers. Another issue is the packaging. Foil bags offer excellent gas barrier properties assuming the seal is perfect and there are no pinholes. Plastic bags, on the other hand, offer poor barrier protection, meaning that even a vacuum-sealed plastic bag can still allow oxygen ingress over time.

My advice is to use hops as soon as possible after purchasing, unless they are packed in foil and clearly labeled with the crop year and processor. The challenges of repackaged hops are well understood, and many hop processors serving the homebrew market have responded by labeling their products with the same information as packs sold to commercial brewers.

Hops do go on sale, and good deals can be found. I love a bargain and feel confident buying discounted hops if I know they were packaged by a reputable processor and properly stored throughout their life. That last piece, storage history, is nearly impossible for any buyer to verify, whether homebrewer or pro. That’s why it’s good brewing practice to smell your hops before use. If you open a bag and something seems off, it’s your call: Repurpose the hops for bittering or make the executive decision to toss them.

Dry hopping isn’t just for IPAs anymore! A dose of citrusy, herbal, or tropical hops in the fermenter can be a wonderful addition to West Coast Pilsner, barrel-aged saison, or amber ale. While one approach to dry hopping might work for a hazy IPA, you may want to adjust your process for other styles. You can trade off concentration, temperature, agitation, and time. Higher concentrations, warmer temperature, increased agitation, and extended time all extract more aromatics . . . but also compounds you may not be as excited about like astringent polyphenols, grassy aromatics, and bitter alpha acids. Let’s take a look at how each of those parameters change the finished beer. 

Hop Evaluation

The first and most important step in dry hopping is to evaluate your hops. Whether it’s a new variety or hops you’ve used before, give them a smell! The quick and dirty way is to rub a few pellets between your palms. I find this to be a more “true” representation of what the hop will contribute to the beer compared to smelling the bag. Rubbing also gives you a chance to evaluate the pellets themselves. Denser pellets are more likely to sink and require agitation to suspend them into the beer. Another option is to follow the American Society of Brewing Chemists (ASBC) method of steeping the hops in cool water for 20 minutes in a French press before pressing and smelling, which we previously covered in “Ingredient Sensory Methods” found online here. 

If you don’t like the aroma of the hops, reseal the bag and use them for a whirlpool addition on your next batch. In most cases a little “weirdness” from the hops will blow off with heat or be scrubbed away by fermentation. 

Combining Hops and Beer

There isn’t anything that ruins a good hazy IPA like oxygen exposure. While the deleterious effects may be more subtle in other styles, I treat all of my beers with the same oxygen-phobia. While brewers (rightly) focus on transfers and packaging, one of the most important and treacherous steps is dry hopping. For our first double IPA at Sapwood Cellars I poured the hops into the top of a 10-bbl tank through the “dry hop port.” Within seconds a plume of hoppy foam was shooting at the ceiling (and raining back down onto me). Think 300 gallons (1,100+ L) of Diet Coke and a case of Mentos . . . After that we learned to add a pound or two of hops, close up the tank and allow it to degas. At home it’s rarely so dramatic, but be careful if you are dry hopping a beer that was spunded or fermented under pressure!

We now use a hop doser from MARKS that attaches to the dry hop port, allowing us to purge the hops with CO₂ and then add them to the beer under pressure. Some homebrewers have similar contraptions fashioned from a sightglass and butterfly valve, and they are a great option if you use a conical or a modified keg with a tri-clamp fittings on the lid.

Another great option is to transfer the beer onto the hops. At the brewery we do this in our infusion tank or brinks (both fitted with mesh screens on the outlets to keep the hops in). We add the hops to the empty vessel, purge it with CO₂, and finally fill it with beer under pressure. As a homebrewer, I did this in a Corny keg with the hops in a tube screen. Fill the screen less than halfway to allow room for the hops to expand and extract. Even still, this may reduce aroma extraction — one study found a 50% drop in extraction of linalool from bagging hops.¹ 

If none of these are options with your equipment, dry hop during the tail end of primary fermentation. Active yeast will uptake oxygen quickly and prevent most of the damaging effects of oxidation. Just be warned, active fermentation dry hopping can promote hop creep (discussed later) and will make it more difficult to harvest and reuse the yeast. 

Temperature

According to that same study, extraction of linalool (fruity aromatic) was nearly as rapid at 39 °F (4 °C) as it was at 68 °F (20 °C). The advantage is that colder temperatures reduce the extraction of the harsh/bitter resins and polyphenols. This study was conducted on a small scale. When we tried it on a commercial scale, we found that the cold extraction requires increased agitation to promote contact between the beer and hops. After our first attempt we found whole unextracted pellets at the bottom of the tank.

Colder dry hopping imparts a more “true to pellet” aroma, with fresher, more intense hop aromatics. That said, it can smell like sticking your nose right into a hop bag, rather than highlighting the citrusy and fruity aromatics. This is because warmer mid-to-late fermentation additions lead to a reduction in myrcene (woody/herbal). I prefer colder dry hopping in beers that are drier and less likely to “stand up” to astringency, including most drier or lower-alcohol beers (e.g., West Coast Pilsner, saison, non-alcoholic beers). For hazy IPAs we usually perform one dry hop addition after soft crashing and another close to freezing to get some of each character. Warmer dry hopping also promotes haze formation by releasing more polyphenols to bind with yeast mannoproteins.

Amount of Hops

Higher dry hopping rates result in diminishing returns. A beer dry hopped with 1 oz. per gallon (7.5 g/L) isn’t twice as aromatic as one with 0.5 oz./gallon (3.8 g/L). That is because it is more difficult to fully extract a larger dose of hops, some compounds saturate, and the green material of the hops reabsorbs compounds already in solution. 

To deal with the extraction issue, you can add dry hops in multiple stages. However, if you don’t have a way to remove the spent hops and introduce another dose without oxygen ingress you may be better off with a single dose. My preference as a homebrewer was to add half of the hops loose to primary and the rest to the keg in a weighted metal tube screen. The hops in primary settle out with the yeast, while the tube screen reduces issues with clogged poppets (at the expense of lower extraction). 

For the absorption issue, advanced hop products can help. I often like to replace 25–50% of the traditional T90 pellets with concentrated/lupulin “enriched” pellets like Cryo Hops^®, T45, CGX^TM, and LupoMax^®. Generally, we use traditional pellets for the first dose and concentrated for the second. Concentrated pellets tend to be higher in oil and more finely ground, and as a result stay in suspension longer even at colder temperatures.

If that doesn’t get you the intensity you are looking for, then hop extracts, oils, and terpenes like Yakima Chief Hyperboost^TM, Abstrax Quantum Brite, and Spectrum from BarthHaas are a great final addition. These are ideal because they can be dosed to taste, even in the glass (an easy way to make hop water if you have a keg of seltzer). While they are often sold for breweries looking to maximize yield by reducing reliance on hop pellets, none of them can completely replace dry hopping. IPAs without actual hops just don’t have the right mouthfeel or breadth of hop flavor and aroma. To my nose they tend to “brighten” the aroma, covering up dull aromatics with more fruitiness. 

Replacing some hop pellets with oils can also lead to a more durable hop aroma. Hops include a variety of compounds that can accelerate staling (e.g., metal ions). Hops can also have air trapped inside the pellets. Adding oils reduces these risks and creates a beer that still smells “hoppy” well after a heavily dry-hopped beer would fade. Extract companies have suggested to me that 2 lbs./bbl (1 oz. per gallon/7.5 g/L) is around the sweet spot for saturating the beer with a variety of hop compounds, and then topping up with oil; though we still most often add 4–5 lbs./bbl (2–2.5 oz./gallon or 15–19 g/L) for IPAs and double IPAs, and I can taste the difference. 

Agitation

There are many options for agitation: Dissolved carbonation in the beer, physical agitation of the fermenter, rousing with CO₂, recirculating pumps . . . I’ve even attached a Mighty Dwarf speaker onto a fermenter, which generates sound by vibrating the object it is placed on! I hooked it up to a tone generator and adjusted the frequency until it created a resonance with the beer.

The most traditional method is to simply allow the trapped carbon dioxide in the beer and produced during the tail end of fermentation to agitate the hops. The risk here is that the CO₂ exiting the beer can scrub out delicate hop aromatics and the yeast can pull some of them out of suspension. That said, the more fragile aromatics tend to be “green” like myrcene, and as a result less desirable in many styles. While I had decent results as a homebrewer with mid-fermentation dry hopping, it never seemed to work for us on a commercial scale. The aroma just never popped, and if we tried to agitate the hops we’d get harsh astringency. These days we rely on whirlpool hops and flowable CO₂ extracts (Incognito^®, DynaBoost^TM, or TerpSauce^®) for “saturated” fruity hop flavor.

As a homebrewer, I would wait a few hours for the tail end of fermentation to purge out the fermenter’s head space after dry hopping. Then I’d rock the closed fermenter to increase contact and resuspend the hops. With 620-gallon (2,350-L) tanks that isn’t an option, so at Sapwood Cellars we use a high-flow CO₂  regulator to bubble CO₂ through the beer for 1–2 minutes several times. I’ve talked to other brewers who will pressurize a piece of hose to send one large “blast” of CO₂ through their beer. 

As tanks become even larger, the only option is to recirculate the beer with a diaphragm pump to keep the hops in suspension. Impeller pumps can pull in air if the seal leaks and can increase astringency by beating up the leaf material. Peter Wolfe’s thesis “A study of factors affecting the extraction of flavor when dry hopping beer” found most hop aromatics peaked between 6–24 hours at room temperature.² This was on a small scale with a relatively low dry hopping rate. Mitch Steele (New Realm Brewing Co.) suggests that anecdotally, he has achieved the best results with “periodic” agitation over the first 48 hours after dry hopping.

If you have an opaque fermenter, pull a sample after rousing to check that the hops are in suspension. Check again in an hour or two to see how well they are staying in suspension to determine how frequently you need to rouse. 

Exposure Time

Traditionally, English brewers dry hopped in the cask until the beer was consumed. Most American brewers now prefer one to three days (although I’ve heard as long as seven). Again though, that really comes down to time, temperature, and agitation. Taste the beer each day and consider stopping your agitation or crash chilling if you’ve achieved the aroma you are looking for or you’re worried about extracting more astringency or vegetal aromatics. Both of these can be difficult to judge on a flat sample, but you’ll learn by tasting and taking notes.

Hop Creep, Diacetyl, ALDC, and GM Yeast

Hops contain amylase enzymes that turn unfermentable dextrins in the beer into fermentable sugars.³ If you are dry hopping warm with active yeast it could happen to you. Zach Bodah of Allagash is credited with investigating this and drawing attention to hop creep in 2017 after a dry-hopped beer over-carbonated during bottle conditioning.⁴ 

In addition to lowering the final gravity slightly, this renewed fermentation can lead to diacetyl (buttery off-flavor). Bob Kunz from Highland Park (Los Angeles, California) suggested we add Alpha Acetolactate Decarboxylase (ALDC) enzyme to a warm dry-hopped West Coast Pilsner we brewed in collaboration with him. ALDC prevents diacetyl production by “skipping” a step and using up the precursor (alpha acetolactate) by converting it to acetoin. As a result, it has to be added at the same time or before the dry hops, as it isn’t effective at removing diacetyl once it is created. Another option is to ferment with a brewing yeast that has been genetically modified to not produce diacetyl (sugh as Omega Yeast’s “Plus” series of strains). 

Hop creep is not a new concept. Gareth Young from Epochal Barrel Fermented Ales in Glasgow, Scotland, showed me a 19th century Scottish brewing textbook that spelled out the exact same issues. Gareth uses the technique at his brewery intentionally to create uniquely delicious mixed-fermentation beers, allowing the enzymes from the whole hops in the barrels to free sugars for an extended mixed fermentation while the hop aromatics interact with the Brettanomyces.

At Sapwood Cellars, dry hopping cold after dropping out the yeast has prevented hop creep . . . but then we store our beer cold after packaging and don’t send much beer out to distribution. As a homebrewer, you can do the same.

Evaluating the Results

IBUs

For a recent triple IPA we targeted 40 IBUs/ppm of isomerized alpha acids in the kettle. That drops considerably through fermentation, and absorption by the green material in dry hops. After dry hopping we sent a sample to Hopsteiner for analysis with HPLC (High-Performance Liquid Chromatography). The result was only 7 ppm of iso-alpha in the finished beer. However, all of the additional hop compounds from the dry hopping added 90 IBUs. The problem is that while alpha acid, humulinones, and xanithohumol are detected as IBUs with the traditional tests looking at light absorbance at 275 nm, they don’t taste as bitter as iso-alpha — that puts the approximate bitterness perception at 27.9 IBUs. All that is to say, it’s easier to talk about the perceived bitterness than the actual “number” of IBUs (especially because residual sweetness, polyphenols, alcohol, and other factors affect how bitter a beer tastes).

pH

Dry hopping raises the pH of the beer. Our solution is to acidify with phosphoric acid in the kettle into the high-4s at the start of the boil. This has the added benefit of lowering the rate of Maillard reactions in the kettle, producing a paler, less “malty” wort. Be warned though, it also lowers alpha acid isomerization (~10% fewer IBUs at a pH of 4.8 compared to 5.2 in one study.⁵ Fermentation drops that pH further into the low-4s. Dry hopping generally raises the pH back to 4.5 or so. That works for us — and helps promote beer stability — but in the end I’d be more concerned about how the beer tastes to you. A little lower pH can help a double IPA read crisper and more drinkable, while a higher pH can cause a pale ale to read richer and fuller. 

Sensory

One of the most important things you can do to improve your beer is to drink it critically and evaluate the results. Whenever I can, I sit down with our freshest batch next to something similar from another brewery. I try to be analytical, noticing trends (are my beers always more astringent, or contain a certain aromatic?). Do I notice a particular note from one of the hops that carried through, or are there aromatics that were lost? Almost as important is the hedonistic “enjoyment” (which beer do I find myself going back for another sip of?).

Tips and Tricks

For a long time, I underappreciated how much the right yeast strain could enhance hop aroma. Don’t be afraid to think like a Belgian when it comes to maximizing yeast character. Consider warmer fermentations, manipulating pitching and aeration rates, and blending yeast strains! Pair a hop variety with a complementary yeast strain. Here are some examples: 

• Cosmic Punch with Galaxy^® (passion fruit)

• Conan with Amarillo^® (stone fruit)

• London with Strata^® (grapefruit)

• Sacch Trois with Citra^® (orange)

• Hefeweizen with Cashmere (banana)

• Belgian with Krush^TM (bubblegum)

Don’t confuse adding more hop varieties with increasing complexity. Most hops contain the same set of aromatics in different ratios. Blending four or five varieties often creates an “average” hop aroma. That’s great if you are a big brewery trying to make a consistent core beer, but not if you want something unique and varietal. Stick to dry hopping with no more than three varieties in a single beer unless you really have something specific in mind. 

Hoppy Time

It’s easy to forget that homebrewed dry-hopped beers start with a huge built-in advantage — freshness! I get to go to Yakima to select hops each fall, have all the equipment and gizmos, and package beers with <30 ppb total package oxygen (TPO), but if that can sits warm for a month it loses that amazing “fresh” hop aroma! Like home cooking, homebrewers also have the advantage of using the ingredients and process that create your ideal beer without worrying about sales, marketing, or consistency! 

References:
¹ Mitter, W. and Cocuzza, S. (2013) “Dry Hopping — A Study of Various Parameters,” Brewing and Beverage Industry International, March, pp. 70–74. www.shorturl.at/CwWEF

² Wolfe, P. (2012) “A study of factors affecting the extraction of flavor when dry hopping beer.” www.shorturl.at/QeiCt

³ Young J, Oakley WRM, Fox G. (2023) “Humulus lupulus and microbes: Exploring biotic causes for hop creep.” Food Microbiol. www.shorturl.at/4LVhY

⁴ Hieronymus, S. (2020) “Brewing with Hops: Don’t be Creeped Out,” Craft Beer & Brewing, October.  www.shorturl.at/FhYn3

⁵ Jaskula B, Aerts G, De Cooman L (2010) “Potential impact of medium characteristics on the isomerisation of hop α-acids in wort and buffer model systems. Food Chem. Vol. 123, Issue 4, pages 1219-1226. www.shorturl.at/TTjLM

Anchovy hops? Are you kidding me?

Yes, there is a new hop called Anchovy. Does it taste like anchovies? Well, no. It is described as having flavors like watermelon, raspberry, and pine. But the name alone is an attention grabber. When a brewery sponsors acreage for a new hop variety, they can sometimes name the hop when it goes into production. This new hop was given the name Anchovy by Matt Storm and Brian Strumke from Fast Fashion Brewing in Seattle, Washington. They wanted to make a beer called “Hot Pizza” with the new hop and thus the unusual hop name choice.

So, is it just marketing? Does it work? Yes. The hop is already sold out in smaller homebrew quantities at Yakima Valley Hops. The name alone got my attention, and other brewers will probably have the same initial reaction. Whether it is hype or not, we makers of beer usually want to brew with hot new hops ourselves.

We are fortunate to be in the golden age of hop experimentation and innovation. The evolution from basic bittering and aroma hops to the nuanced, complex flavors found in modern hazy and juicy beers has opened up a whole new world for brewers. With the soaring popularity of these “juicy” beers came hop flavors in addition to just bittering or aroma. The range of flavors and aromas that can now be achieved with different hop varieties and techniques is truly staggering. It is a very exciting time when it comes to the science of beer, giving homebrewers the opportunity to benefit from all this science to make better beer.

The variety of new hops hitting the market every year is, indeed, a big part of the thrill for us homebrewers. Each new hop variety brings its own unique profile — some with tropical fruit notes, others with floral or piney characteristics. The challenge and excitement lies in finding the right combination to create a beer that really stands out. Add to this the discovery of different ways to use hops in the brewing process and we have even more creative and varied flavor profiles. It might just be time to explore these new hops and redesign a few of those old recipes.

In this article, I’ll delve into the latest hop varieties to become available to homebrewers, examining their unique characteristics and how they can be integrated into your brewing process. Whether you’re looking to craft a groundbreaking IPA or refine a classic style, these new hops offer fresh possibilities to enhance your creations.

Note: Some of the hops listed here are designated by a combination of letters and numbers. Those that start with “HBC” are from the Hop Breeding Company, a joint venture by Yakima Chief and John Haas. This collaboration led to the development of Citra^®, Mosaic^®, and more; “HS” = Hopsteiner, which is also located in the Yakima valley; “YQH” = Yakima Quality Hops.

Alora^TM (previously HS17701)

The name Alora is of Latin origin meaning “beautiful dream, dreamlike, or divine light.” Alora is best known for its unique oil composition. Unlike most hop varietals that contain what those in the industry call the “big 8” oil groups (pinene, myrcene, limonene, linalool, caryophyllene, farnesene, humulene, and geraniol), Alora contains over 50% of unidentified total oil uncommon in hop chemistry. Further analysis has revealed a large percentage of this “unidentified” category type to be selinene – a sesquiterpene rarely found in hops. Selinene is a low-volatility compound that imparts distinct citrus character directly into finished beer and can be found in fruits such as calamondin oranges and yuzu fruit.

Aroma

Peach, yuzu fruit, sweet melon, apricot

Typical Analytical Range

Alpha Acids: 7–10%
Beta Acids: 3.5–4%
Total Oil (mL/100 g): 0.8–1.3

What Pros are Saying

Obed Salazar – Assistant Brewmaster, North Coast Brewing Company 
“I have used both Alora and Anchovy with great success. I preferred the expressiveness of Alora over Anchovy because the aroma was perceived as actual fruit (yuzu and sweet melon) when compared to the pleasant but slightly candy-like aroma of watermelon that I perceived from Anchovy.” 

Darren Stankey – Marketing Manager, Hopsteiner
“I have done trials, and found in the wild, combinations that use Sultana, Lemondrop, Lotus, and our latest experimental HS16660 with Alora (are) all excellent combinations, but Alora is also great as a single-hop recipe.”

Anchovy 

Initially, it went by the name 24B-05 but was given the controversial name Anchovy by Matt Storm and Brian Strumke from Fast Fashion Brewing. Fast Fashion was the first brewery to sponsor acreage, so they got first cracks at brewing with it and the beer was well received. There is a limited amount of this hop available, but the expectation is acreage, and availability, will increase in the coming year.

Aroma

Watermelon, raspberry, pine

Typical Analytical Range

Alpha Acids: 11.5%
Beta Acids: 3.6%
Total Oil (mL/100 g): 1.4 

What Pros are Saying

Steve Gonzalez – Sr. Manager of Brewing & Innovation, Stone Brewing Co.
“Anchovy has a lot of depth. Some overt watermelon and green notes on the front of the palate with some interesting, sweet aromatics and a touch of dankness on the back end. It’s a fun hop to use as a substitute in ale styles for hops like Citra^® or Amarillo^®, also for hops with long finishes and real depth of flavor! Could it work in lagers? We’re about to test that, but I don’t know for sure!”

Elani® (Previously YQH-1320) 

Elani^® was discovered by Yakima Quality Hops Owner Tim Sattler in Idaho’s St. Joe River Valley and is likely the result of open cross-pollination. Tim brought rhizomes back to Yakima Valley and after years of trials it hit the market in 2022. Tim describes Elani^® (pronounced ee-LAH-nee) as “clean and bright. With tropical, citrus, and stone fruit.” 

Aroma

Pineapple, guava, lime, white peach, orange zest

Typical Analytical Range

Alpha Acids: 9–11%
Beta Acids: 6–7%
Total Oil (mL/100 g): 1.3–2

What Pros are Saying

Geoff Belcher – Head Brewer, New Realm Brewing Co. (Charleston, SC)
“I got to trial this hop early on as YQH-1320. The hop sounded beautiful with the citrus and stone fruit notes in the descriptor in particular . . . The first beer I brewed with this was a 100% Elani^® cold IPA to really see what this hop was all about on a super clean canvas and to let those citrus and stone fruit notes shine. It did not disappoint! (A recipe for this beer is below.) “For the homebrew environment I would say this hop plays well with Citra^®, Simcoe^®, Centennial, Nelson Sauvin, as well as many others.”

Krush^TM (Previously HBC 586) 

Originally bred in 2007 by the Hop Breeding Company experimental hop variety program, Krush went through a thorough 17-year process as an experimental variety and was officially released as a commercial hop brand in 2024. Krush bursts with citrus (orange), tropical (mango, guava), stone fruit (peach), berry (mixed berry), and woody (resin) characteristics that deliver complex, ripe, and punchy aromas.

Aroma

Berry, citrus, stone fruit, tropical, woody

Typical Analytical Range

Alpha Acids: 10–14.1%
Beta Acids: 6.3–9.4%
Total Oil (mL/100 g): 1.3–3 

What Pros are Saying

John Leingang – Head Brewer, Nine Mile Brewing
“Citrus, pine, tropical tones, stone fruit notes . . . so complex, for sure!

“It does tend to take over other hops if used it higher amounts.”

Michael Tonsmeire – Co-Owner/Brewer, Sapwood Cellars
“We recently released a dry-hopped mixed-fermentation with it in collaboration with Mieza Blendery (Experimental Phase) and dry hopped a DIPA (Boy Have You Lost Your Mind) with it a few years ago. It has a really over-the-top stone fruit, almost-thiolized, character to me . . . It has given some really bright fruit-forward aromatics without much green/dankness. I tend to like beers with a balance of fruit and other more ‘savory’ balancing notes to remind the drinker that it isn’t just juice, so I like to pair it with a Citra^®/Simcoe^®/Mosaic^® if there isn’t something like the underlying funk of a barrel-aged sour.”

Vista 

The newest hop variety released from the USDA public breeding program. It was selected by brewers in blind smell tests at Yakima Valley Hops back in 2019. They ranked it 7/10 on a potency scale. It should work well in IPAs and pale ales, but it is also a good fit in lagers and Pilsners.

Aroma

Tropical fruit, tangerine, melon, pear, green tea

Typical Analytical Range

Alpha Acids: 11–12%
Beta Acids: 4–5%
Total Oil (mL/100 g): 1–2

What Pros are Saying

Eric Sannerud – Sannerud Hop Consulting 
“The strongest aroma I perceive is melon. I like that it is bright, clean, and dry.”

John Leingang – Head Brewer, Nine Mile Brewing Company
“Overall, Vista tends to be an amazing supporting hop with pretty much any newer American varietal. It’s got range to exist in a bunch of different styles of beer, usually as a stalwart support role. Vista has been a crucial key player in terms of brightening up the other varietals (Idaho 7 and El Dorado).”

WCHB-102 (Previously 2B) 

This is the second hop to be released by West Coast Hop Breeding and gained notoriety among many when hyped up by John Kimmich at The Alchemist. The hop shows superior disease resistance and is attractively priced. This “late-pick” hop is vigorous and can be grown both conventionally and organically. WCHB-102 has a clean, citrus-forward profile with hints of lime zest, melon, and pine resin, and a high aroma impact of apple and pear. This hop can stand alone or be paired to increase the layered, rich range. 

Aroma

Citrus, lime zest, melon, pine, apple, pear

Typical Analytical Range

Alpha Acids: 11.2%
Beta Acids: 5.3%
Total Oil (mL/100 g): 1.82

What Pros are Saying

John Kimmich – Co-Owner/Brewer, The Alchemist Brewery
“I have had very successful results using this hop. I have used it in several batches of Skadoosh over the last couple of years, and they have all been very pleasing. I was drawn to using it when I first was given a small sample of the first crop a few years back. Unique and interesting to say the least.

“I have used it as a single-hop, which was great, and I’ve used it with various others. It could certainly stand alone, but it loves to be complemented with the right choice of additional varieties”

Eric Sannerud – Sannerud Hop Consulting
“One of the few hops I have given a 5 in sensory analysis. The apple/pear aroma will work well with a variety of other hops and adds complexity.”

Zumo 

Discovered in the Segal Ranch open-pollination hop nursery years back, Zumo was first released in 2023 and is already becoming a favorite amongst breweries such as Other Half, Stone, and Russian River. Brewers who have already brewed with Zumo describe it as citrus, citrus, and more citrus. A prominent lime note makes it a perfect fit for Mexican lagers, but it has also performed well in big IPAs.

Aroma

Lime zest, orange, citrus

Typical Analytical Range

Alpha Acids: 5.5–6.5%
Beta Acids: 4–5%
Total Oil (mL/100 g): 0.5–1 

What Pros are Saying

Vinnie Cilurzo – Owner, Russian River Brewing Company 
“The aroma is delicate but that is OK as the lime quality the hop gives the beer is distinct. We are using it in our 2024 release of Pliny for President in the dry hop. It also works really well in a beer we make called Zumo Wresting, which is technically a West Coast Pilsner.

“A positive for the hop is the fact that it does not have super high alpha acids, and thus a brewer can use more of it in the whirlpool and not see the bittering units jump up too much.”

Steve Gonzalez – Sr. Manager of Brewing & Innovation, Stone Brewing Co.
“Lots of both bright, fresh, and also warm lime and candy flavor from this hop. I prefer it in fuller-bodied IPA styles like juicy hazies and in dry-hopped lagers. It performed just fine in West Coast IPAs, but it really needs a lot of malt character to express itself best for me, whether that is Pilsner malts or a generous helping of malted wheat and malted oats. The low bitterness from this hop makes it safe to go heavy handed on the whirlpool side!”

There are a couple more hops I want to highlight because they are making waves in the craft beer scene, though the supply in the homebrew market is limited right now. We expect they’ll become more widely available to homebrewers soon:

Experimental HS16660 

Experimental HS16660 has yet to receive a name, but we wanted to highlight it for its high-intensity aroma that is high in geraniol composition and even higher in free 4MMP thiols — which are responsible for the sought-after flavor and aroma of tropical and sweet fruits. The 4MMP thiol levels land off the charts in comparison to other hop varieties. 

Aroma

Tropical fruit, berry, fruit candies, citrus

Typical Analytical Range

Alpha Acids: 10–13%
Beta Acids: 3–4%
Total Oil (mL/100 g): 2.3–2.8

What Pros are Saying

Darren Stankey – Marketing Manager, Hopsteiner
“HS16660 will be receiving a name soon. It has already been a hit with brewers who have trialed it and folks are coming back for more. Keep a look out for this new one that will be making its commercial debut soon.”

Peacharine 

From Freestyle Hops in New Zealand, Peacharine has a rich peach/nectarine character with an appealing citrus backbone that includes sweet fruit, lime zest, and indistinct floral notes. Homebrew quantities are hard to come by, but given the positive press it has gotten from the pros who have used it (such as Trillium, Toppling Goliath, Tree House, The Alchemist, Fidens . . .), we’d expect availability to increase in the near future. Peacharine can be used in a single-hop beer, but also pairs well with a wide range of both thiol- and terpene-heavy varietals like late-harvest New Zealand Cascade.

Aroma

Peach, nectarine, citrus, sweet fruit, lime zest

Typical Analytical Range

Alpha Acids: 6.1%
Beta Acids: 6.2%
Total Oil (mL/100 g): 2.1 

What Pros are Saying

Geoff Belcher – Head Brewer, New Realm Brewing Co. (Charleston, SC)
“I honestly think Peacharine is super unique and nothing would really be close on substitution. I’ve found that it plays nice with your more resinous Chinook, Cascade, and Simcoe^® hops.” 

Excited to brew with some of these new hop varieties? I know I am. To get started, two pros  interviewed for this story were gracious enough to share proven recipes featuring a couple of the highlighted varieties, found below.

Hops are considered an essential raw material for beer due to the preservative and functional properties of their chemical constituents. The hop acids (alpha and beta acids) have been well documented to lend antimicrobial and antioxidative protection to beer as well as impart bitterness, foam, and textural quality. 

Of course, varieties are also sought after for the distinct flavors/aromas that their essential oils provide. Varieties like Citra^® and Mosaic^® are well known for their citrus and tropical characters, Lemondrop^® is lemony, Saaz and Styrian varieties are floral and herbal, and Cascade reminisces grapefruit. As a result, hops can still be divided into aroma varietals and high-alpha varietals, although many aromatic varietals are also relatively high in bitterness potential (dual-purpose hops).

Historically, hops were harvested, processed, and stored with the intent to maintain alpha acid content. Alpha acids are generally considered most impactful for their contribution to beer bitterness. Once structurally rearranged through boiling, they become isomerized-alpha acids (isomerization is literally a structural rearrangement of the atoms in a molecule), which are more soluble in beer to lend bitterness. Other players, such as beta acids and polyphenols, also affect beer bitterness. Oxidation of beta acids leads to bitter molecules and polyphenols can enhance bitterness due to their astringent nature — and both will augment the analytical bitterness measured in the bitterness unit (BU) by spectrophotometric measurement. Hop chemistry is dynamic, as the accumulation of these secondary metabolites is heavily impacted by hop genetics, growing environment, and harvest timing/practices. Chemical changes such as degradation, oxidation, and rearrangement subsequently occur during post-harvest practices: Kilning, pelletizing, and storage.¹ Modern-day practices aim to reduce these impacts and as a result  brewers now have some of the freshest and best-preserved hops ever available for brewing.  

The question that begs asking is — what makes a hop fresh and how does this translate to quality? 

Hop Storage Index

The Hop Storage Index (HSI) is a well-established metric used to assess the relative level of oxidative change that occurs during hop storage. The methodology was developed by Nickersen and Likens in 1979.² It is a simple analysis to assess how a hop ages from harvest to use. The higher the HSI, the poorer the hop variety fared from harvest to storage and through processing. The measurement is conducted using a spectrophotometer and is non-specific in that it measures the absorbance at 275 nm to 325 nm of an alkaline methanolic extract of hops. A harvest-fresh HSI should be below 0.300.^3,4 Harvest HSI is varietal-dependent, with many traditional varieties (Hallertau Mittelfrüh, Hersbrucker, Tradition, Perle, Taurus, and Herkules) scoring less than or equal to 0.275, noble hop varietals like Czech Saaz scoring a bit higher, and some more recent varietals like Celeia scoring above 0.300. Generally, aroma varietals show lower HSI while high bittering varietals like CTZ tend to score higher at harvest. 

HSI scores trend upward as hops hang on the vine, particularly for the high alpha acid content hops. Higher kilning temperatures also lead to higher HSI values, for example a shift from 140 °F to 170 °F (60 to 77 °C) can increase HSI by 15%.⁵ Higher baling pressure and storage temperatures can also augment HSI. However, once pelletized, properly packaged under inert gas, and cold-stored (typically 28 to 39 °F/-2 to 3 °C), HSI should remain stable for several years until use. 

While the hop storage index was developed over 40 years ago, it remains the most common tool used to measure alpha and beta acid degradation from harvest to pelletization. HSI is a necessary metric to understand when contracting hops based on alpha acid content. 

Interest in Hop Flavor/Aroma Changes During Storage Began More Recently

While a depth of work has been done to study post-harvest practice effects on hop acids, fewer studies have looked at storage effects on the hop volatile oil components and the brewing quality of aged hops from a flavor perspective. We know that as the hop acids break down, the release of their side chains result in organic acids that impart rather undesirable aromas. The cheesy and sweaty-sock notes of iso-valeric acid and pungent, baby vomit notes of butyric acid appear rather readily upon hop oxidation, exposure to heat, and light. As hop acids degrade, their oxidized products still lend bitterness, however the bitterness has typically been deemed less desirable. Despite not smelling fresh, brewing with aged hops can actually lend desirable fruity aromatics to finished beer. Organic acids esterify into much more pleasant stone fruit, cherry, and peach aromas in the presence of ethanol. Historically, aged hops have been used in the production of sour beers such as lambics. With significant aging, the degradation of the hop acids detracts from their preservative effects and allow lactic acid bacteria and non-Saccharomyces yeasts to do their work. The resulting fruity esters also blend nicely with the sour notes of traditional lambics and other fruited beers. 

In non-sour beers, these qualities are less desirable, especially for lagers that aim to impart kettle hop aromas and ales that are expected to be accompanied by fresh hop notes. Researchers took an interest in evaluating the effects of hop storage on hop volatiles in the late 1970s and early 1980s. During this time, post-harvest practices were shifting in the hop industry and hop pelletization first became available. Pelletization removed upwards of 10% of the vegetative matter and resulted in a more compact product that could be efficiently shipped and stored. Pellets were also thought to be a more stable form of hops to keep in storage. At this time, refrigeration of bales in storage was still not common practice, however brewers were interested in the use of pellets that had the potential to store longer under refrigeration in the brewery. 

I recently spoke with Val Peacock, longtime hop chemist and hop guru at Anheuser-Busch and now a hop consultant, about his experience in the hop industry when these changes were taking place. Conversing with him about “hop quality” really opened my mind. My experience with hops begins after the popularization of both pelletization and extraction capabilities, and so what I know, or we might define collectively, as “hop quality” today is vastly different than how a brewer might have defined hop quality 50 years ago. 

In Old Germany the Hop Warehouses Smelled Different: A Conversation with Val Peacock 

According to Val, 50 years ago people thought that aging hops was positive. If you would talk to European brewers in the 1970s and earlier, there was a disagreement/confusion around what “noble hop aroma” was. Beers were full-flavored, brewed using 100% malt, and had 20–30 IBUs. He recalls the legendary brewing scientist Morten Meilgaard, most remembered for his sensory work and development of the beer flavor wheel in 1979,  referring to noble hop aroma in beer as “reminiscent of hops, but not hops” — an aroma that actually doesn’t last very long in the beer. 

Before refrigerated storage in Europe, this would be before the 1980s, bales were not as densely packed as the bales we see today. Bales were more like hop pillows — they were round and stacked rather loosely in piles. Farm bales were later repackaged into higher density bales for shipment to buyers. As Val recalls, “Those warehouses smelled different, more like tobacco or leather and less like the myrcene-driven hop smell we witness today,” when we walk into a hop processing facility. The pillowy farmer bales in Europe pre-1980s were packed at about half the density of today’s bales. Hops were stuffed into a burlap bag (which also gave flavor to the hops). The empty bag was about 2 meters tall and one meter across (6.6 x 3.3 ft). The moisture content was higher, closer to 14% than the 10% it is currently in the U.S. These fluffy bales would sit in warehouses without temperature control where, in a temperate climate, they would not dry out as much as they would in the more arid Yakima Valley of the U.S. These 12–14% moisture bales would sit in farmers’ storage until January, at which time they were delivered or shipped to customers. At such high moisture content, the bales would produce a hop sweat with biological processes going on. If they were too wet they could get very hot. So the bales had to be loosely packed and not as stackable to allow for plenty of circulation. Because of this, flavor components would be altered. He noted that Anheuser-Busch eliminated the use of burlap bale wrap in the 1990s because of the odor it imparted to the hops. What was considered noble hop aroma in beer was different than today, and thus these beers might taste different than beers today. 

In the early 1990s the German industry also changed their baling practices. The pillowy bales were replaced by square bales that were 50% more dense. These bales could be stacked much higher and thus would take up less warehouse space. At the time, the industry seemed more interested in economics than hop aroma, and the main goal was to avoid alpha acid losses during storage. These more densely packed bales were more prone to sweat and the heat buildup in the bale could
lend toward spontaneous combustion. 

At the time, most warehouses were not refrigerated, and many today globally are still not refrigerated. This is not only a threat to hop aging, it is also a threat to the hop farmer and processor. Spontaneous combustion has been the cause of many warehouse fires. Even as recently as 2006, fires caused from high-moisture bales actually destroyed hop warehouses in Yakima Valley, estimated to cause about $4 million of damage. Approximately 4% of the U.S. hop yield was lost in this one fire.⁶

As Val recalls, once cold storage was more readily available the nature of the hops’ aroma also changed. Commercial brewers were fine with it as they were largely focused on the bittering resins; refrigerated hops resulted in reduced alpha acid loss from bale-to-beer. 

Commercial U.S. brewers 30–40 years ago may have sourced about 1⁄3 of their hops from Europe and 2⁄3 from the U.S. At the time (1980s), beers were becoming increasingly lighter and less bitter. Take for example the original Miller Brewing Company “Lite” beer. Miller Lite was originally in the 20 BU range, whereas today it has only 10 BUs. These lighter beers did not have enough malt backbone to mask the tobacco notes and the lingering harsh bitterness from aging hops was not acceptable with the lower BUs, further pushing the hop industry to invest in refrigerated storage. 

In the 1980s, most commercial brewers were using hops in their leaf form. Whole leaf hops would be shipped from Europe or Yakima and be stored up to two years in cold storage at the brewery. From the time hops were harvested, dried, baled, and shipped on a boat across the ocean or via rail in January, hops were already many months old before use. 

According to Val, Anheuser-Busch switched to pellets in 2003. Coors was using whole cones up until the 1990s and Miller was using extracts as early as the 1950s. In the 1990s the major lager producers were pressed to switch to hop pellets that took up less space in storage, were more efficient to use, and kept better than whole cone hops under proper packaging and refrigeration. 

“Sensory challenges weren’t much of an issue, hops were now less aged and bitterness was perceived to be smoother in quality. The consumers didn’t seem to mind or were not providing a lot of feedback, as no one seemed to be calling in and saying, ‘you changed my beer,’” Val said.

It was a brewing culture shift that did not receive a lot of pushback. Anheuser-Busch had been trialing pellets 10 years before the final switch was made. Coors and Miller had been doing studies on hop pellets and hop products even earlier. In the midst of this culture shift from whole cone to pellet hops seems to be when brewers found a need to investigate the effects of pelletizing and less aging on hop and beer flavor. 

Hop Baling Practice Shifts in the U.S.: Conversation with Hop Grower Diane Gooding 

Let’s hop back to baling practices for a bit. After learning about some bale history in Europe, I was curious to know more about bale history in the U.S. I reached out to Diane Gooding of Gooding Farms in Idaho. In Idaho, hops used to be put into sacks and a person, generally a really big guy, would literally stamp them down. These sacks would be loosely packed and weighed about 70 lbs. (32 kg) (interestingly, Diane noted that the Spanish hop industry still uses these types of sacks). Hops were dried and stored in the warehouse in piles, baled in winter, and delivered in the spring. Cable balers in the day were pulled by oxen or horses in a circular fashion. The time between picking and baling was extended just as in European practice. 

Today, Gooding says from the time her hops are picked from bines in the processing shed it takes five minutes to get them to the dryer. The hops are kilned for an average of 9.5 hours (timing varies based on the hop variety, kiln bed depth, and kiln temperature). Hops are then cooled for 12–24 hours. Sometimes farmers don’t have time to dry them 12 hours due to the demands of harvest. This can lead to inconsistencies in the hops. A modern bale weighs 200 lbs. (91 kg) and is more densely packed than in the sacks so they must go into cold storage until pelletized. While it would be ideal to process into pellets within two months, the reality is that in the U.S., most pellet operations often run until mid-March. Once hops are pelletized, they are generally more stable, depending on the oxygen content of the mylar bags they are packed in. Most producers flush bags with an inert gas and can get the oxygen levels down to 0.05–0.1% oxygen. However, sometimes oxygen can get as high as 1.5–2%, and this can have a big impact on HSI. 

It is important to note that hop processing is still not uniform in the U.S. There are different types of pickers, drying systems, kiln bed sizes, pellet types, and packaging practices. 

Hop Volatiles Change Due to the Use of Fresher hops 

In the 1980s, researchers at Oregon State University and Adolph Coors Brewery conducted research to understand the effect of using fresher hops on beer flavor.

In the early 1980s, Val Peacock and Max Deinzer of Oregon State University (OSU) published their work investigating the effects of refrigeration on hops and the essential oils subsequently transferred to beer.^7,8 Six varieties of hops were aged for one year under refrigerated storage (Hallertauer, Perle, Hersbrucker, Tettnanger, Cascade, and Cluster) and evaluated for hop oil and acid changes. The varieties in which alpha acids degraded most also showed the most oxidation of humulene. During storage, geranyl isobutyrate had converted to a more flavor-active form, geraniol. Today, geraniol, its precursors, and related compounds are known to impact beer aroma. This study is one of the earliest works to show the importance of geraniol and its biotransformation during beer production.

In 1985, Foster (Adolph Coors Brewery) and Nickerson (OSU) published their work on hop oil degradation of 20 different hop varieties over six months at ambient temperature. Not surprisingly, most hops lost a significant amount of total oils. However, losses were varietal-dependent ranging from 27.5–90%. A comparison of pellets and cones of three hop varieties also revealed that hop cones lost from 53–62% of total oils and pellets lost from 43–58% of oil after 30 days of storage.⁹ Oxygen resistance is higher for cones than pellets under aerobic conditions. In the production of pellets, hops are milled to be pressed through a die. Milling of hops into a powder disrupts the lupulin glands and leaves them more accessible to oxygen.¹⁰

The 1980s studies on hop aging identified humulene oxidation products as contributors to the traditional “kettle-hop” aroma of beer. Even under one year of refrigerated storage, humulene oxidizes to humulene epoxide II. We don’t find humulene epoxide II in beer produced with fresh hops because wort boiling times do not seem to be long enough to convert measurable amounts. Humulene epoxide II from aged hops does extract into beer and as beer ages it converts to humulenol II (this is seen over a typical beer shelf life). Peacock and Deinzer identified humulenol II as a contributor to “fine hoppy aroma”⁷ and suggested that its content can affect hoppy beer aroma.

To better understand the impact of fresher hops on beer flavor, researchers at Adolph Coors again teamed up with scientists at OSU using Washington-grown Cascade and Idaho-grown Hallertauer Mittelfrüh hops.¹¹ Beers were brewed in 30-barrel pilot batches with hops of three categories: Fresh hops, hops aged at 90 °F (32 °C) for two weeks (Aged I), and hops aged at 90 °F (32 °C) for nine weeks (Aged II). Flavors of the aged and fresh hop beers were discernably different for both varieties (confidence level 95% and higher). 

This early work showed that hop volatile content during the stages of brewing is in fact a very dynamic process. Some compounds decrease from wort production to finished beer, while some compounds increase from wort production to finished beer. Moreover, some go up and down, or vice versa. One such example is citronellol that was only observed post-fermentation. Citronellol is a product of yeast biotransformation on geraniol precursors. Most hop oxidation products of alpha humulene and B-caryophyllene poorly survive fermentation. Some esters such as ethyl octanoate and ethyl decanoate can be detected in samples after fermentation. The floral compounds of linalool, geraniol, and alpha-terpineol generally survive the brewing process and can be found in finished beers from most hop varieties. In the Coors collaboration with OSU, the intensity of kettle aroma (herbal/spicy) decreased with aged Cascade hops, yet increased with aged Hallertauer hops. The highest floral ratings were given to beers with Aged I hops over fresh hops in alignment with geraniol, linalool, and citronellol content. Again, humulenol II was not found in the fresh hop beers, while the herbal spicy note was found in the aged hop beers, and more prominently in the Aged II Hallertauer hopped beers. A grapefruit-like citrus note was also detected in beers brewed with extensively aged (Aged II) Cascade and Hallertauer hops. 

The 1980s studies concluded that fresh hops indeed made a difference to beer flavor and that “moderate aging of fresh hops prior to brewing” was positive as it maximized the level of desirable aroma compounds. 

Similar studies were recently conducted to assess the impact of aged hops on IPA flavor.¹² In beers brewed with Simcoe^® and Saaz that had been exposed to five different aging conditions, the authors concluded that moderate aging may make beer more drinkable and that old hops contribute a “unique” flavor (undefined). The results were in agreement with the beers brewed at Adolf Coors Brewery in 1985.

What’s interesting to me about this data is that during my first Cascade hop selection for Coors brands in 2010, I was astonished at the hops we selected as “high quality.” To me, the hops were already a bit oxidized, grassy, and herbal. I was so accustomed to smelling the fresher Cascade hops used in hoppy Pacific Northwest craft beers. It turns out these hops had been selected year over year for the past 25 years in alignment with the 1985 scientific data that Bob Foster had collected during his time as a hop chemist at Coors. 

Fresh Hops Today

Today, we are much more accustomed to the smell of myrcene and citrus in our hops. The hops we use today are undoubtedly fresher than they were 40 years ago. The heavy dry hop loads of craft culture depend on the fresh piney and citrus aromas in hops. Some processors today tout the freshness of their pellets. The reality, as Diane Gooding reminded me, is that not all hops are pelletized right away. Only some breweries are fortunate to brew with hops pelletized with minimal storage. During the months between baling and pelletizing, even under refrigeration, HSI increases. And with that, hops will lose alpha and beta acids. 

Hop volatiles immediately begin to shift from bale to pellet: Myrcene will undergo auto-oxidation to produce several other attributes such as beta pinene, geraniol, geranial, linalool, and nerol, and humulene will begin to oxidize to its “kettle hop” counterparts.¹³ The longer a bale sits in cold storage before pelleting, the more they will age. In some hop growing regions such as Slovenia, many growers do not have refrigerated storage,¹⁰ which means when in surplus (as in 2020) their hops surely will age if not processed and used quickly. This amount of aging may not be appropriate or acceptable to brewers. 

Assessing Hop Quality and Long-Term Hop Storage

What makes a hop high quality? It appears that hop quality is truly in the hands of the brewer. The best way to assess hop quality is through sensory analysis in a good old-fashioned hop rub. The only standard for hop age in the industry we have is HSI, which does not adequately address all metrics of “hop quality.” Research from 2023 suggests that high-HSI hops can absolutely be used effectively to produce high-quality beer — depending on the variety. While beers brewed with hops of an HSI of 0.3 were overall statistically higher in hop aroma quality than beers brewed with hops with HSI 0.5, the researchers suggest that Celeia and Aurora hops, with an HSI of up to 0.5 and Styrian Wolf, with an HSI of up to 0.6, are indeed suitable for beer brewing.¹² The authors do not have any justification other than it must be due to the presence of some as-yet-unmeasured compounds or the occurrence of some as-yet-unidentified synergistic effects between compounds in the aged hops. 

Typically pellets have a higher starting HSI than fresh hop cones and also have a higher HSI after aging (under aerobic conditions), with some exceptions that seem to be varietal-dependent as volatile profiles tend to reflect genetics. Effectively, both storage conditions and hop variety play a role in hop stability. The range of changes in volatiles appears to be more closely related to the starting essential oil content than to the oxidative changes among volatile compounds.¹¹

Although the project is very much in its infancy, just a few months ago Thomas Shellhammer’s lab at Oregon State University presented preliminary results of their latest studies on hop aging.¹³ The research is exploring the aging characteristics of American aroma hops and initial results suggest that when stored properly (i.e., satisfactorily sealed, intact, gas-flushed high-barrier packaging with very low oxygen content, and stored frozen) hops show only modest declines in quality over 4 years and in some cases were not significantly different (chemistry and aromatic qualities) from samples that were less than one year old. There was some varietal dependency, but initial experiments show Citra^® and Hallertauer Mittelfrüh being quite stable over four years. Centennial displayed modest changes while Cascade showed the most age-dependent changes. Further work is needed to assess the specific chemical and sensory changes in American aroma hops as they age, and work is ongoing.

In my own experience, hops stored properly can last upwards of four years. While at MillerCoors I would sometimes get called over to the brewery to smell a freshly opened bag of hops. My nose was used to determine whether they were good enough for use. Even after three or four years in our coolers, they were almost always still fresh to my nose.

To Recap 

The hops of yesterday were not as we know hops today. Post-harvest processing and storage practices lead to herbal and earthy aromas, which are very different than the citrus, floral, and piney aromas today’s consumers are accustomed to. Modern day post-harvest processing and packaging significantly reduces the effects of oxygen and temperature on hop acid degradation during storage, however there is still a window of time where hop cones await pelletization that can stretch to many months. We do not fully understand the changes that these hops undergo, yet we do know that hop variety seems to play a role in how hops “age” and that storage conditions will affect how quickly hops change. Our industry metric for aging, HSI, does not adequately address all the metrics of “hop quality.” The brewing value of high-HSI hops is not necessarily degraded with age, as the data tells us that moderately aged hops can positively impact beer aroma. 

References

¹ Identification and Quantification of the Oxidation Products Derived from Alpha-Acids and Beta-Acids During Storage of Hops (Humulus lupulus L.). J. Agric. Food Chem, 2013, 61, 3121-3130.

² Nickerson, G.B., Likens, S.T. Hop Storage Index. J. Am. Soc. Brew. Chem, 1979;37(4):184–7. 

³ Cocuzza, S., Lutz, A., Müller-Affermann, K. Influence of Picking Date on the Initial Hop Storage Index of Freshly Harvested Hops. MBAA Technical Quarterly, 2013;50(2):66-71.

⁴ Weber, K., Jangaard, N., Foster, R. Effects of Postharvest Handling on Quality of Storage Stability of Cascade Hops. J. Am. Soc. Brew. Chem, 1979;37(2):58-60.

⁵ Zunkel, From Hop Harvest to the Brewery. www.barthhaas.com/ressources/blog/blog-article/from-hop-harvest-to-the-brewery

⁶ “Huge Hop Fire” ProBrewer. www.probrewer.com/beverage-industry-news/huge-hop-fire

⁷ Peacock, V., Deinzer, M. Chemistry of Hop Aroma in Beer:, J. Am. Soc. Brew. Chem, 1981.

⁸ Peacock, V., et. al. Hop aroma in American beer. J. Agric. Food Chem, 1980, 28, 774-777.

⁹ Foster, R.T., Nickerson, G.B. Changes in Hop Oil Content and Hoppiness Potential (sigma) during hop aging. J. Am. Soc. Brew. Chem, 1985, 43, 127-135.

¹⁰ Rutnik K, Ocvirk M, Košir IJ. Changes in Hop (Humulus lupulus L.) Oil Content and Composition during Long-Term Storage under Different Conditions. Foods, 2022 

¹¹ Lam, Kai C., Foster II, R., Deinzer, M. Aging of Hops and Their Contribution to Beer Flavor. J. Agric. Food Chem, 1986, 34, 763-770. 

¹² Xu, H., et. al. Aging of Hops and Their Effects on India Pale Ale Flavor. BIO Web of Conferences, 2023.

¹³ Rutnik K, Ocvirk M, Košir IJ. The Impact of Hop Freshness on Kettle-Hopped Beers. Foods, 2023.

While lagers and clear IPAs seem to be enjoying a resurgence in popularity, hazy IPAs continue to dominate beer menus at home and in the taproom. Hazy IPAs came to prominence around the time I co-founded Omega Yeast Labs in 2013. While the science wasn’t understood at the time, brewers found certain yeast strains more reliably produced the desired extreme, orange juice-like turbidity. Sales of our British V strain (known from other providers as London Ale III, London Fog, Juice, and Foggy London) grew steadily along with the growth in popularity of hazy IPA. Adjuncts like oats and wheat are also used to boost haze potential, but the common thread among the best examples was the yeast strain. What is it about the yeast strain that made it so good at creating this haze? Was it possible that certain strains had a “genetic predisposition” to creating haze?

From penicillin to the physics of microwave ovens, many scientific discoveries stem from a fortuitous observation not even connected to the goal of the immediate experiment. Our discovery of the “haze gene” in yeast is no different. Our R&D Director, Dr. Laura Burns, and research scientist, Keith Lacy, were conducting flask-based experiments to study hop creep based on dry hop timing. Hop creep refers to the release of dextrin-degrading enzymes (amylases) that break down long carbohydrate chains to release fermentable sugars. 

The experimental setup was simple — wort with a specific gravity of 1.060 was prepared from 2-row base malt and distributed to flasks. Two popular strains were chosen to control for strain-dependent observations — West Coast Ale I (i.e., Chico) and British Ale V. Each flask was inoculated with yeast followed by a dry hop at the same time the yeast was pitched in flask one; day one into fermentation in flask two; day two in flask three; etc. through day seven. The goal of the experiment was to determine if earlier dry hop timing accelerated the drop in gravity caused by amylase enzymes in hops, thereby speeding up hop creep.  While we were able to make interesting observations about dry hop timing and hop creep, the more exciting observation was related to haze in the final product. Visually, the flasks ranged from super bright to massively hazy. For British V, the later the dry hop, the hazier the beer. For West Coast Ale I, very little haze was seen in any flask. 

This simple experimental setup to study hop creep became known as our “haze assay” and has been wielded to make dozens of observations relating to strain variation, dry hop timing, dry hop dose rate, and dry hop variety that will be discussed in this article. We used the assay to characterize our strain collection into haze-positive (like British V) and haze-neutral (like West Coast Ale I) strains. 

The haze assay gave us an opportunity to conduct some genetic experiments to hopefully identify the genetic component of haze. Ultimately, we wanted to know the mechanism behind the haze-positive phenotype (trait). We generated a hybrid strain by crossing British V to a haze-neutral wine strain (yes, certain strains can undergo a sexual cycle to make new strains). To our surprise, the resulting hybrids were split between haze-positive and haze-neutral (in genetics terms 2:2 segregation). This pattern of inheritance suggested that the haze-positive phenotype was dominant and linked to a specific gene, and from there we set off on our quest to find the haze gene. This seems pretty straightforward, but it was way more complicated than we had anticipated.

We next took one of the haze-positive hybrids and “backcrossed” it with the original haze-neutral wine strain. And again, we tested the resulting hybrid yeasts for haze status in our haze assay. We repeated this six more times and by doing so, we “diluted out” the British V genes — except for the gene responsible for the haze trait. Finally, we compared the whole genome DNA sequences for the hazy hybrids from the last backcross to the original British V and wine strain genomes. By doing so, we were able to locate a gene from British V in the last backcross that wasn’t present in the wine strain or the non-hazy backcrosses. 

Luckily, we have a full-time bioinformatics scientist on staff because this project went down a deep hole of complicated genetics. Using modern technology, including long-read sequencing data, led us to a gene with an unknown function, which we named HZY1. Excitingly, we saw extreme variation from strain to strain in the type of HZY1 gene that a strain had. The HZY1 gene seems to be prone to mutations that involve repetitive DNA resulting in versions (alleles) of the gene that are anywhere from 580 base pairs (bp) to >2,500 bp. Within any given strain, we found up to five different versions of HZY1! Consequently, it isn’t a straightforward answer for which version causes haze, but we found a strong correlation between longer versions of the HZY1 gene and the haze-positive phenotype. However, even our haze-neutral strains contribute to small degrees of haze (think the small amounts of haze in most dry-hopped beers). When the HZY1 gene is disrupted in every brewing strain we have tested, the resulting dry-hopped beers are significantly less hazy.

While uncovering the HZY1 gene was exciting, it didn’t answer the question: How does yeast cause haze in beer? We still don’t know for certain, and experiments continue. We do, however, have some good hints about how this gene could physically lead to haze from the DNA sequence itself. The HZY1 gene encodes a secreted glycoprotein (i.e., a protein with sugar molecules attached to it that is sent outside the cell) that is anchored to the cell surface; very similar to the FLO genes that encode the cell surface proteins that lead to flocculation.

The HZY1 gene is heavily glycosylated and we can detect the HZY1 glycoprotein in the haze particles (~500 nm colloids) that form after dry hopping with haze-positive yeast. The particles are actually visible under the microscope! At this point, we can confidently say that stable haze shouldn’t rely on yeast cells in suspension, but yeast-derived HZY1 glycoprotein will do the trick. In other words, flocculation is completely unrelated to haze status. A common misconception has been that you need non-flocculent yeast to make hazy IPA. If you take one thing away from reading this, let it be that you don’t need non-flocculent yeast to make hazy IPA. There are flocculent yeast that make hazy IPA (British V is quite flocculent) and there are non-flocculent yeast that will not produce the haze brewers seek. While it’s true that non-flocculent yeast will make hazy beer, it’s not the stable, colloidal haze that is common in the best hazy IPA — eventually those yeast will drop to the bottom and the beer will be clear. 

If you’re reading this and thinking to yourself, “I don’t make hazy beer and I don’t care about any of this,” our haze research isn’t all about making hazy beer. It has helped us understand a lot about avoiding haze, too. The brewing strains you use have a version of HZY1 that either leads to a small amount of haze or a large amount of haze. If you want to make a dry-hopped beer that is brilliantly bright, chances are good that getting rid of HZY1 in your house strain will make that easier. Knowing the haze status of your strain will get you closer to the outcome you desire for your beer. In other words, it is an uphill battle to make clear dry-hopped IPA with the British V strain. It is inherently prone to making hazy beer due to its genetic makeup. 

We still have more to learn, but we ultimately hope to make the execution of hazy and non-hazy beer more of a science and to provide brewers with more tips, yeast options, and predictability when designing their IPAs.

Other Haze Factors

We have discovered many factors that impact haze by altering variables in our haze assay. The guidance provided by these observations can be used by the homebrewer to create haze in beer when they want it and avoid it when they don’t. After months of testing, several important factors influencing haze began to stand out:

1. Yeast Strain

When we looked at the rest of our strain collection, we found that British V was not unique and there were a handful of brewing strains that produced significant haze. In our flask fermentations, yeast that produced >200 NTUs (nephelometric turbidity units) with a late fermentation dry hop at 8 g/L (about 2 lbs./bbl or 5 oz. per 5 gallons) were termed “haze-positive” (blue in Chart 2). There is extremely useful information in this chart. You wouldn’t want to bang your head against the wall trying to make hazy IPA with Chico, for example. You might be able to get mildly hazy beer by utilizing adjuncts like oats or wheat, but you’re not going to get orange juice-level haze with Chico. Conversely, if you’re attempting a modern take on a crystal clear Kölsch-style beer by including a dry hop and Kolsch I (OYL-017) is your strain of choice, it is going to be exceedingly difficult to get it clear because Kolsch I is genetically prone to haze in combination with dry hopping. Don’t fight genetics! 

2. Dry Hop Timing

Our experiments have shown that dry hopping close to the end or after fermentation is best for inducing yeast-derived haze. Late dry hop = more haze. The good thing about this is that it allows you to harvest yeast before dry hopping without fear of losing haze potential. Harvesting yeast after dry hopping can cause lots of viability problems. 

Conversely, dry hopping in the first 24 hours leads to less haze and can even prevent haze from forming with later dry hop additions. This is one of the most interesting and confounding observations from our research. To this day, we don’t know the mechanism, but a very small dry hop (e.g., ½ oz. or less per 5 gallons, or 14 g/19L) at the same time as you pitch your yeast can help make your beer clear. This even works with haze-positive yeast! We’ve had professional brewery customers implement this technique in recipes where they have had difficulty achieving clear beer and it has helped tremendously. Try it the next time you’re making a clear lager. 

3. Dry Hop Dose Rate

Testing dry hop rates of 1.3, 2.5, 5, 7.5, 10 oz./5 gallons (37, 71, 142, 204, 284 g/19 L), we found a linear correlation to the amount of haze formed: The heavier the dry hop, the more the haze. Keep in mind though, hazy is hazy. By eye you might have a hard time telling the difference between skim milk and whole milk — both are pretty opaque! There are diminishing returns in aroma and flavor quality with higher dry-hop loads and the same is true for haze. 

4. Hop Variety

This part of the research is surprising and likely provides some clues into how dry hopping is leading to the yeast-dependent haze. What component of the hops is providing the signal or is part of the haze particle? We don’t currently know why, but different hop varieties lead to different amounts of haze with various combinations of haze-positive and haze-neutral yeast (see Chart 3). Some varieties of hops, like Enigma^® and Sabro^®, provide a decent amount of haze even when used with a haze-neutral yeast. Some varieties, like Galaxy^®, provide huge amounts of haze when used with haze-positive yeast strains but provide very little haze when used with haze-neutral strains. Hop suppliers might be onto something with hop products that stabilize haze and we are keeping a close eye on their findings.

Conclusions

As history has shown again and again, you never know where you’re going to end up when you track down a scientific observation. A lesson I learned as a graduate student was to never conduct experiments with blinders on. You might be setting up an experiment to examine a particular problem, but if there are unexpected observations, you might be led somewhere far more fruitful if you follow the unexpected path. 

As you can now appreciate, the opaque haze that we have come to love and expect in hazy IPA is largely a result of the particular type of HZY1 gene that a yeast strain possesses. That’s not the whole story, however. In tracking down the HZY1 gene, we made observations that are useful to brewers when formulating a new beer. One must consider the strain, the dry-hop timing, the dry-hop amount, and the hop variety when considering the amount of haze desired in the final product. All of these variables have a profound effect on the outcome. 

We know a lot about how to produce stable haze, but does haze contribute to flavor, mouthfeel, or aroma? We’ve now conducted multiple experiments with breweries using a version of British V that has the HZY1 gene removed to make beer along with the traditional version of British V in parallel. While it’s simple to visually distinguish the beers, tasters have statistically been unable to distinguish them when the beers are served in opaque cups. This doesn’t necessarily diminish the importance of haze in beer because we do “drink with our eyes,” but it is amusing nonetheless that brewers spend so much time and energy making a beer clear and consumers have expectations associated with haze, but none of it matters strictly from a taste or aroma perspective. 

Where do we go from here? Nature has provided us with a large amount of variation when it comes to dry hop-induced haze and the HZY1 gene, but what if we want to make hazy beer with Chico yeast? Now that we know the genetic basis of haze, it is possible to move a haze-inducing version of HZY1 into Chico for stable haze while maintaining all the traits we love about it, including minimal esters and good hop aroma expression. What if we want the fruitiness and soft mouthfeel of British V, but the clarity of a West Coast IPA? We can, and have, knocked out the HZY1 gene from British V in a new strain now available called DayBreak-V (OYL-408). This provides exciting opportunities to merge styles. Soft, yeast-derived fruity esters in a crystal clear dry hopped beer merges the traits of West Coast IPA and hazy IPA to create something fresh and exciting. Brewers, including those of you reading this, will probably discover new applications for these modified strains that we’re not even contemplating — and that’s why yeast scientists do what we do!

Q: I was recently reading an article from the BYO archives about recipe formulation, and the part about hop prediction lead me to a question: What is meant by “boil efficiency”?
— Greg Wilhelmi • Boone, Iowa

A: The term “boil efficiency” typically refers to “hop utilization” and relates hop alpha acids added to wort to iso-alpha acids in beer. I will use the standard term “hop utilization” in this answer to prevent any confusion with the term “boil efficiency” as that makes me think of other things like evaporation rate and heat transfer rate.

For starters, let’s digest the basic definition of hop utilization and review why hop utilization has a practical maximum of about 40% for large commercial breweries and about 30% for homebrewers and most craft brewers. Hops contain alpha acids, among other hoppy components, useful to brewers. When hops are boiled, alpha acids contained in hop lupulin glands soften and dissolve into wort. It turns out that alpha acids have very limited solubility in aqueous solutions because they are hydrophobic (water fearing). Hydrophobic compounds tend to literally stick together in aqueous solutions and when they are less dense than the solution they float to the surface. Think of vegetable oil added to a pot of boiling water; the oil is visible as large, amorphous, balloon-looking blobs. When foam develops in a pot of boiling pasta, chicken stock, or wort, oils are carried with the foam and some of these oils are deposited on the surface of the pot above the liquid level. We see this when cleaning pots after boiling wort, pasta, and chicken stock. This relates to hop utilization because oil, aka alpha acid, loss is one reason why hop utilization is less than 100%.

Aside from getting hop acids to stay in wort and away from the surface of the kettle, another key of hop utilization is the conversion of hop alpha acids into iso-alpha acids. When alpha acids are heated above about 176 °F (80 °C), they begin to morph or isomerize into a different group of compounds named iso-alpha acids. Turns out there are several types of alpha acids and each type morphs into a specific iso-alpha acid. Chemistry aside, this transformation depends on temperature, time, pH, and wort density. As wort density increases, isomerization rate decreases (although iso-alpha acid solubility increases). And as temperature, time, and pH increase, so does the rate of isomerization. It’s worth noting that while increasing wort pH increases isomerization and hop utilization, it also decreases the quality of bitterness, increases wort color, changes the way malt proteins precipitate, and has a negative effect on beer stability. Suffice to say, increasing wort pH is not something brewers do to increase hop utilization.

Because hop utilization compares hop alpha acids added to wort to iso-alpha acids in beer, wort boiling is just one part of the process where losses occur. Iso-alpha acids are more soluble and less hydrophobic than alpha acids, but they are still sticky and have limited solubility in wort (that’s why the limit of beer bitterness is about 120 IBUs, regardless of marketing claims made on beer labels). Alpha and iso-alpha acids are also lost to trub, fermenter surfaces contacted by beer foam during fermentation, some beer finings, filtration surfaces, and anytime in the process when beer foams. One practical way to increase hop utilization is to use anti-foams during wort boiling and fermentation. But your question is not about how to increase hop utilization, just what it is.

The next question, how does a brewer know what value to use when calculating hop additions, is easy to answer but far from easy to assess. The easy answer is to compare iso-alpha acids in beer to hop alpha acids added to wort. Duh! However, most small-scale brewers, both home and craft breweries with limited production, don’t know the iso-alpha acid content of their beers because the testing method requires special equipment, is time-consuming to perform, and uses a solvent that must be properly captured and disposed of after use. The other challenge is knowing how much hop alpha acids were added to the kettle.

Let’s tackle this last point first. Because the hop alpha acid content is printed on all packages of hop pellets and hop cones, knowing how much was added seems simple. Right? The problem is that alpha acids oxidize during hop storage and the value printed on the bag changes over time. When hops are packaged and stored properly, the rate of alpha acid change is slow. Therefore, using the value on the package is not a bad place to start if we recognize what we are dealing with. And as luck would have it, alpha acids oxidize into a group of bitter compounds called humulinones. While humulinones are less bitter than iso-alpha acids, they do preserve some of the bitterness and do not represent a complete loss when hops oxidize. In practice, however, this poses a challenge because it means that hop storage plays a role in hop calculations. Let’s just leave that idea and keep moving!

The real challenge in this whole thing is knowing the iso-alpha acid content of beer to develop prediction models. The homebrewing hop models developed by Rager, Tinseth, and Garetz in the early 1990s are all problematic because none of the methods make any mention of how utilization was measured. Please correct me if I am wrong, but I cannot find anything written by these authors documenting how they went about determining utilization. Not to cast shade because their efforts helped many brewers with hopping. The good news is that larger breweries do routinely measure iso-alpha acids in beer, and we know enough to be able to come up with some pretty safe assumptions.

Table 1 is a synthesis of utilization rates from several sources plus some massaging. It’s important to know that any utilization rate from a table is some form of a guesstimate; without knowing what goes into the kettle and what ends up in the beer, we simply do not know what happened. This is why many brewers don’t get too worked up over calculated IBUs. When calculations are performed consistently and adjustments are made based on perceived bitterness, the numbers are simply a means to an end. I hope this sheds a useful light on your question!