Pay a visit to any industrial-scale brewery and you will discover that fermentation takes place under tightly controlled settings. Temperature is a key component. Brewmasters knew exactly what temperature they want for each fermentation tank, depending oFn the brew being produced. That temperature is maintained throughout the process.
Homebrewers care about temperature too. But without commercial-grade equipment sold by manufacturers like Houston-based Cedarstone Industry, maintaining the right temperature during both primary and secondary fermenting is not that easy.
Why does it matter? Because fermenting temperature affects the ultimate taste of the finished beer. Ferment at too high a temperature and you create one type of adverse flavor. Fermenting at temperatures that are too cold results in a different flavor. In either case, it will not be what you are hoping for.
Fermenting at High Temperatures
Under ideal conditions, ales should ferment at temperatures ranging from 68-72°F. Lagers are fermented at anywhere from 45-55°F. A few degrees on either side will not harm most beers. But anything more drastic than that could cause trouble.
Fermenting at too high a temperature causes yeast to go into overdrive. Remember that during the fermentation process, yeast is converting glucose into alcohol and carbon dioxide. Fermentation actually feeds the yeast.
The end result of fermenting at high temperature is two-fold. First, you tend to get a flavor that is excessively fruity. Some people have described it as tasting like exceptionally powerful bananas. Others have described their overly fruity beers as tasting like chewing gum.
The second thing brewing at high temperatures does is increase fusel alcohol content. Fusel alcohols are known for their harsh flavors. They have been described as being hot, spicy, or tasting like household solvents. None of the possibilities sound particularly good for homebrewed beer.
Fermenting at Cool Temperatures
If you have to err on one side or the other, it is better to ferment the beer at temperatures that are too cool. The worst that can happen is that you will not get the rich, robust flavor you’re after. The reason for this is simple: cold yeast doesn’t do as good a job converting glucose. Yeast is a living organism and, like you, doesn’t perform well when it’s cold.
Some homebrewers still prefer to ferment at cool temperatures because they feel they get a less bitter product. They compensate for a less active yeast by letting their product ferment for a longer period of time. Under optimal conditions, ales are fermented for about two weeks; lagers ferment for up to six weeks. Fermenting under cool conditions could add a week or two.
Controlling Temperatures at Home
Homebrew hobbyists utilize all sorts of hacks to keep their fermentation vessels at the right temperature. They understand that fermentation naturally produces heat, thereby requiring them to monitor temperatures throughout the entire process.
If things get too warm, one option is to employ an evaporation hack. You place the fermentation vessel in a tub of cold water and cover it with a piece of cloth — like a towel or T-shirt. As the cold water evaporates, it cools the fermentation vessel.
Another hack is to pack the lower half of the fermentation vessel in ice. This draws heat out of the vessel by a process known as thermal transfer. This is considered a more aggressive means of controlling temperature.
Controlling fermentation temperature is important because it affects the taste of a finished beer. It is so important that commercial breweries invest tens of thousands of dollars in temperature-controlled fermentation tanks. At home, you have to make do with whatever you have.
