Brewing Tasty Beer? Simulate It with CFD!
Most of us might have walked through beer factories enjoying and trying to understand the overall culinary process of beer brewing. And with the Oktoberfest now happening in Bavaria, the topic becomes very popular.
A simple online search for the steps involved in the brewing process leads to few common steps. There are even websites, like How to Brew, purely addressing the brewing process. Some of the steps include:
- Brewing the beer: Involves boiling of pale malt extract and hops with water. Further on, the grains are steeped frequently to add color and flavour.
- Cooling and fermenting: Here the hot mixture, now known as wort, is cooled to room temperature and further on transferred with additional water. Once the cooling occurs, yeast is added and locked in an airtight container for fermentation.
- Priming and bottling: Once the beer is ready, it is transferred to another container for priming. Here sugars like corn sugar are added. Further on, beer is siphoned into bottles.
- Aging: Once the beer is bottled, it will need again 2-6 weeks during which the yeast will ferment the remaining sugar to create carbon dioxide. The carbon dioxide will naturally carbonate the beer.
Of course, once the beer is properly aged, it is put in the fridge to enjoy drinking!
Brewing Tasty Beer and Simulation
The natural question that arises here is how simulations can help here, be it industrial or home brewing? There are several areas in which simulation can help with making a better beer. Two of the main areas are fermentation and cooling. While fermentation is a more complicated thermo-chemical process, cooling is a much simpler thermal problem.
Cooling of Wort
An important aspect of the brewing process that can control the taste of the beer is the cooling of the wort. Here the boiling wort is cooled down very quickly to the temperature where the yeast can survive. Yeast has a survival temperature between 30 – 40 ℃ and is the most comfortable around the body temperature. High temperatures, of even 50 ℃ can be significantly damaging to the survivability of the yeast. Hence, the boiling wort needs to be drastically cooled. In home brewing, the general volume is smaller but in the beer industry, the volume is much bigger.
In addition to the survival temperature of the yeast, it is also important to consider the production of by-products like off-flavours made of sulphur compounds and other contaminants. Fast cooling also reduces the production of these by-products. Some of the simple ways of cooling could be adding ice or playing the entire unit in an ice bath. But both of these techniques are not efficient.
Alternatively, wort chillers are used and they consist of long helical pipes that can be immersed in the wort container at the end of the boiling process. Further on cold water is circulated through the pipes to cool the boiling wort. An inspiration for such a wort chiller can be found in the “Cooling System Flow Analysis” project available on the SimScale public projects database. A simple model of the wort chiller is as shown in Fig. 02.
Fig 02: Simple model of a wort chiller (from “Cooling System Flow Analysis” project)
In the above project, only a fluid flow analysis is considered as an incompressible flow process. However, an additional external volume can be added to model the overall process as a conjugate heat transfer process. Alternatively, the brewing process can consider using a heat exchanger.
“Heat Exchanger – CHT simulation” project in the library provides an appealing template for modeling the cooling of wort using a heat exchanger. “Heat exchanger,” as described on Wikipedia, is a device used to transfer heat between one or more fluids. The heat exchanger, shown in Fig. 03, uses water as a coolant to rapidly remove the heat from the boiling wort.
Fig 03: Heat exchanger for modeling wort cooling. Full model (left); internal pipe system (middle); external pipe system (right)
The cooling process can be modeled as a conjugate heat transfer process. The heat exchanger is made of copper and the cooling liquid is made of water. The hot wort passes through the outer tubes while the cold water passes through the inner tubes. The cold water cools the hot wort to the desired temperature as it passes out of the heat exchanger.
As the inner fluid (water) flows through the inner pipes (grey color), the wort is passed through from end-to-end in the outer set of pipes (blue color).
Fig 04: Temperature profile of the outer (or wort)
The temperature profile of the outer fluid is shown in Fig. 04 and the inner fluid in Fig. 05. In Fig. 04, the hot wort passes through the heat exchanger through the top opening and into the outer pipe system. As the wort passes through the heat exchanger, the heat energy is transferred to the coolant liquid (or water here). As the wort exits the heat exchanger from the bottom outlet, the wort is cooled down to the desired temperature (here room temperature).
Fig 05: Temperature profile of the inner fluid
Similarly, Fig. 05 shows the temperature profile of the coolant liquid (or water) flowing in the inner tubes. As it can be seen, water enters on the left side at low temperature and exists on the right side. As the water exits, the temperature of the water is higher due to the heat absorbed from the wort.
Such a heat exchanger is the most efficient and fastest way to cool the boiling wort. A simulation (CFD analysis in this case) of the heat exchanger process, as shown above, can significantly help to improve the brewing process and render more tasty beer.
Another aspect of the brewing that can be modeled in an ad-hoc manner is the process of fermentation. The fermentation process is reasonably complicated and involves reaction dynamics of various chemical processes. The process can last from a few days for a simple Ale to several weeks for a Lager. This is the point during the brewing process when the brewer decides on the type of beer and adjusts the temperature accordingly. If it would be an Ale, the temperature is adjusted to about 65-76 degrees while for the Lager, it is much lower and around 45-55 degrees. At these temperatures, the yeast consumes all the sugars. Even after the fermentation stops, the yeasts continues to absorb the off flavours that are produced like sulphur etc that are produced. Once the off-flavours have been removed, the yeast becomes dormant and settles down at the bottom of the fermentation vessel.
There have been several people who have discussed the beer fermentation model. Of their papers, one of the prominent ones is the work of Gee & Ramirez . As discussed by them and also from a general understanding, the process of fermentation involves heat generation due to breaking down of the sugars (Glucose, Maltose, and Maltotriose). In addition, ethanol and biomass production rates, production of amino acids (nutrients) and production of fused alcohols-esters etc (for flavors) also need to be accounted.
Overall, all these chemical changes lead to a heat generation and a natural convection process. The rates of individual reactions and their heat generation can be calculated through chemical reaction equations. The process inside can be modeled as a natural convection process as shown in Fig. 06.
Fig 06: Fermentation during the beer brewing process. This can be considered a natural convection process.
Currently, SimScale does not facilitate solving pre-defined equations related to the chemo-mechanical process here. But this is definitely a module to look forward to. However, SimScale already facilitates CFD simulations that allow modeling of natural convection processes. The overall fermentation process can be considered to be a convective flow process with an internal source of heat. Some examples of these ideas are available in the public projects library like the convective flow with an internal heat source (for example, a light bulb).
Overall the beer brewing process is a complex chemo-thermo-mechanical process and is highly intricate. There exists no technology that can simulate the complete process. In fact, in spite of brewing beer for centuries, there are several aspects of brewing that remain a mystery like the dependence of the beer taste on the local water. Yet, the intermediate steps involved can be easily simulated using today’s computational technologies to improve the overall quality of the beer.
 D. A. Gee & W. F. Ramirez, “A Flavour Model for Beer Fermentation,” Journal of the Institute of Brewing, Volume 100(5), pp. 321 – 329 (1994)
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