In order to consistently create delicious, flavorful beer, home brewers must focus on each and every step of the brewing process, all the way from milling the grain to carbonating the finished product. Temperature of fermentation is one of the most important of these factors to consider, yet it is often overlooked or underestimated by the amateur brewer. For those who wish to take their brewing to the next level and gain more control over the process, however, temperature manipulation is absolutely essential.
For South Floridians, that primarily involves cooling the beer, since ambient household temps in the Sunshine State seldom fall below 75 degrees and we don’t have cool basements to store our fermenting brew. Beer that is left in the linen closet or pantry often ends up fermenting in the 80’s, since yeast activity creates additional heat energy. For some Belgian styles, these temperatures are favorable, but most beers could significantly benefit from a much cooler fermentation.
In general, ale yeast will produce crisper and "cleaner" beer at lower temps, and more "fruity" and flavorful beer when warmer, especially when the temperature is controlled at the beginning of fermentation during reproduction and respiration. Furthermore, once active fermentation is starting to wane, warming up the beer often helps attenuation (the amount of sugars the yeast converts to alcohol). So temperature control helps the brewer not only regulate the flavors the yeast will produce, but also the amount of sugars that will be left behind when fermentation is complete.
There are a lot of ways to keep beer cool during fermentation, and the method that you choose will depend on how much you are willing to spend and what level of control you desire. Most brewers who are on a budget start with the simple “wet towel” method, which involves draping a moist towel over the carboy and relying on evaporation to cool the beer. This is the simplest and cheapest method, but usually only reduces temps by 3-5 degrees. Adding a small fan will get you a couple more degrees, and placing the carboy into a plastic basin with a few inches of water will help too, as it gently soaks into the towel and evaporates.
Intermediate options include ice baths, insulated “ale cabinets,” or even the use of a window air conditioning unit enclosed in a small space of some kind. Many creative individuals have even devised complex recirculating systems that transfer cool water or glycol around the carboy as the beer ferments. The simplest method, however, is to purchase a refrigerator or chest freezer and attach a temperature controller. A freezer is preferable since it is capable of chilling to lower temperatures for those who want to “crash cool,” lager their beer, or experiment with “ice distillation.” The only thing one must remember is that a temperature probe placed inside the freezer will measure the air and not the fermenting beer. You will need a “thermowell” and a compatible probe in order to regulate the temperature inside the carboy.
Making great beer means paying attention to every detail, and for South Florida brewers “Keeping it Cool” should be one of the top priorities during the brewing process. Along with pitch rate, aeration, and sanitization, temperature control is one of the most important factors to consider when it comes to making really great beer.
Good luck and happy brewing!
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