Better Brewing: Modeling Beer Fermentation

June 6, 2024

Brewers have worked on their craft for centuries, testing ingredients and tweaking the fermentation process to produce ideal-tasting beer. Dependent on the initial sugar content, type of yeast, and process temperature, fermentation has been a challenging process to predict since its discovery. Given this variability, in-depth analysis can be especially impactful on the beer brewing process. With the help of the COMSOL Multiphysics® software, we can examine the fermentation process and identify ways in which it can be fine-tuned to produce optimal flavor and alcohol content.

What’s Been Brewing?

Humanity’s fondness for fermented drinks goes back thousands of years ago, with beer-like beverages first appearing in places including China and ancient Mesopotamia. Beer developed over time across civilizations, being used as a form of payment in ancient Egypt, finding a home in medieval European monasteries, and fueling revolutionary talk in England’s American colonies. The close relationship people have had with beer is a long-standing tradition, and its creation continues to be a focus to this day.

Close-up view of two people clinking glasses of beer.
Beer brewing has a long and refreshing history. Cheers! Photo by Markus Spiske on Unsplash.

During fermentation, sugars are converted into alcohol, CO2 is released, and flavor compounds are formed. How well the process goes can mean the difference between a delicious drink and an unusable batch. With so much at stake and with several variables at play, multiphysics simulation can ease the stress of crafting the right beer by introducing precision and predictability into the brewing process.

Exploring the Fermentation Process

Let’s consider the four basic ingredients that make up beer:

  • Water
  • Starch source (malted barley)
  • Fermentation catalyst (yeast)
  • Flavoring (hops)

Before the fermentation process can begin, the barley grains are soaked and dried to form malt, which is then boiled and mixed to convert the released starches into a sugary liquid called wort. Hops are then added to the boiling wort, and the mixture is cooled down using a heat exchanger. Cooling is necessary to prepare the wort for the next stage of the brewing process: fermentation. Fermentation usually occurs in a closed tank that is under anaerobic conditions. Once the wort has been cooled to a temperature lower than 20°C, yeast is added into the mix and the wort starts to ferment. Fermentation typically takes weeks, but the time frame varies depending on the type of yeast used and the fermentation temperature.

Two blue, large-scale beer brewing tanks outside of a brewery.
Large-scale beer brewing equipment outside of a brewery in Vermont, USA.

Once the sugars have been converted into alcohol and CO2 and various flavor substances have been produced, we are left with a product that we can now refer to as “beer”. When it comes to how fermentation proceeds, the yeast type, temperature, and initial sugar content all play an important role. COMSOL Multiphysics® can be used to predict fermentation outcomes.

Modeling Fermentation with COMSOL Multiphysics®

In our model — which is available for you to try out yourself in the Application Gallery — we model the fermentation process using the Reaction Engineering interface, assuming that the system is perfectly mixed (i.e., that the reaction rate is not limited by mass or heat transfer). In the model setup a yeast type that thrives at temperatures close to 12°C (ideal for brewing lagers) is used, and the sugar content is considered to contain maltose, glucose, and maltotriose. Using the model we can evaluate several parameters affecting the final alcohol content, the taste of the beer, and how long fermentation will take.

In addition to accounting for the different types of sugars, our perfectly mixed model analyzes the concentrations of two flavor compounds that result from the fermentation process: ethyl acetate, or EtAc, and acetaldehyde, or AcA. EtAc (an ester) gives beer a desirable taste, while AcA (an aldehyde) imparts an unpleasant flavor. In this setup, both the initial temperature and the temperature in the cooling medium of the tank are set to 12°C.

Plots representing the simulation results of the perfectly mixed model, including the changes over time of the sugar-type concentrations (top left), alcohol content (top right), ethyl acetate and acetaldehyde flavor compound concentrations (bottom left), and temperature (bottom right).

We can see from the results that, over time, all of the sugars decrease while the alcohol content grows. As the first plot indicates, all of the glucose has been consumed after 90 hours. We can also see that this fast glucose consumption corresponds to the initial increase in temperature. After the temperature peaks near the 250-hour mark (i.e., after approximately 1.5 weeks), the alcohol content has surpassed 5.5 percent and the concentration of the bad-tasting acetaldehyde has begun to come down. To reach a low-enough acetaldehyde concentration for an acceptable taste, the beer must be allowed to ferment many hours longer (while the alcohol by volume increases). If we were actually tinkering with this beer recipe, we could initially add more yeast to the wort to accelerate the decrease of the acetaldehyde content.

Last Call: Fermentation Throughout Time

The model results help explain why the brewing industry relies on a timeline of multiple weeks for fermentation. Even at 250 hours, the results show a fermentation process that requires more time but lays the groundwork for future, delicious beer recipes. If we continued tweaking the fermentation process variables in our model for long enough, we could produce results that could be enjoyed anywhere, anytime — from a Roman taverna to a modern microbrewery.

Looking to approach the bar and try out the perfectly mixed model yourself? Explore step-by-step instructions for how to set it up and download the model here:

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