Home Pasteurization

Q. I am interested in experimenting with home pasteurization. Over the years, I’ve read that adding fruit to fermented beer, backsweetening cider, and now making no- and low-alcohol beer are all good candidates for pasteurization. Is there a way to pasteurize at home without embarking on some sort of crazy project?
Taylor Carter
Lille, France

Mr. Wizard says…

A. Although Louis Pasteur is best remembered for milk pasteurization, his original method was developed for beer. And the cool thing about the process we now call pasteurization is that it’s pretty darn simple.

Until the advent of in-line heating and cooling, pasteurization was a batch process. In fact, batch pasteurization is still commonly used by small-scale producers to render products safe and shelf-stable. But the history of beer is more about how advancements in science and engineering allowed brewers to grow large. Pasteurization is at the heart of that history. Brewers were quick to take note of Pasteur’s Études sur la bière (Studies on Beer), and Carlsberg was the first brewery to pasteurize beer for commercial sale in the 1870s. 

As my mentor and professor to many Dr. Michael J. Lewis repeated in every lecture on packaging: Pasteurization allows a brewer to sleep at night. In practical terms, this is because worries about microbiological spoilage and unwanted secondary fermentation are simply erased. 

The good news is that you can easily pasteurize beer at home with just a few simple pieces of equipment. Depending on your setup, you may already have the basic tools. But before discussing how, let’s review the what. Pasteurization at home is performed using a batch method. In essence, this is just atmospheric canning: Prepare a hot water bath, load it with bottles of beer, and process at a set temperature for a set time. A typical pasteurization process used for the range you ask about is 50 Pasteurization Units (PU), where 1 PU = 1 minute at 60 °C (140 °F). The relationship between temperature and pasteurization rate is exponential, expressed as:

PU = t x 1.393^(T-60)

Where “T” is the product temperature in °C and “t” is time in minutes. Using this equation, it’s easy to see why just a few degrees make a big difference. For example, 1 minute at 65 °C (149 °F) equals about 5.2 PU, so 10 minutes at that temperature yields roughly 50 PU. The current recommendation for non-alcoholic beers is about 75 PU, or around 15 minutes at 65 °C (149 °F). The time and temperature together are known as the thermal process.

The main challenge with all types of pasteurization is starting the timer at the right moment. If your process is 15 minutes at 65 °C (149 °F), the timer doesn’t start until the coldest spot in the bottle reaches 65 °C (149 °F). Commercial producers use in-line probes and in-package sensors for this. Smaller producers often use a test bottle fitted with a thermometer to monitor the process. 

If you want to pasteurize at home, one key is to use far more water in your water bath than the mass of product added. This helps prevent a big temperature drop when you add your bottles or cans. A properly sized heater and water pump are also needed. In a nutshell, a large reservoir of water is heated to a temperature a couple of degrees higher than your target process temperature. Because bottled beer has a large thermal mass, you need a heater capable of making up the heat loss. That’s the engineering part of this answer that I’m choosing to skip — but for the curious, that means considering the heat transfer coefficient between glass and liquid, the specific heat of the product, and the total wattage required to maintain a uniform thermal field. Even a 1500-watt immersion heater, when coupled with a small circulation pump, can maintain a 20- to 25-liter bath with less than ±0.5 °C variation (5–7 gallon bath with less than 1 °F). Circulation eliminates stratification and ensures that every bottle follows a near-identical heating curve. For the more technically inclined, thermocouples or data loggers can be used to integrate the pasteurization curve and calculate total PU delivered. After the bottles are added, the process sensor is monitored, the timer started once the target temperature is reached, and the bottles removed after the timer has elapsed.

Over-pasteurization can result in cooked or oxidized beer. Cooking can be controlled by establishing the minimum process required to achieve your goals, and oxidation is minimized by reducing oxygen pickup during packaging. The key point is that the thermal process should be ended by cooling as soon as possible after pasteurization is complete.