Every year at about this time we like to address the question of Summer season fermentation. The amount of heat you actually need to protect against or remove is relatively small, and easy to do. There is no reason you can't make good beer in warmer weather, and in fact you may find your favorite batches happen to come from warmer times, when the yeast tends to produce more esters. Those esters can make more complex and fruitier aromas you may actually prefer. But again, you can easily control those temperatures under most circumstances and in most regions, doesn't require air conditioning your house.

Let's first consider how the beer responds to air temperature changes. The thermal capacity of 5 gallons of beer wort is pretty large. To recognize that all you have to do is think about how hard it is to cool after cooking. Just as beer is in no hurry to cool down, it is not in any huge hurry to warm up! That means as the air temperature rises, the beer temperature rise will be way, way behind. Also, think about the typical warming and cooling on most days. Air temperature increases for part of the day, and then usually cools down quite nicely. If on a given day the high temperature is 85 and the low is 65, the average temperature is 75. But in our climate there will usually be a longer period of the coolest rather than the warmest temperature, resulting in the median temperature remaining well below the average temperature and making daytime heating less of a problem than you may have thought. In other words, it is a matter of time of exposure at any given temperature and thermal capacity.

As the air temperature rises, the beer absorbs heat energy but lags far behind the air. The beer temperature rise stops when the air temperature cools to or below the beer temperature. Then the beer responds by cooling until the cycle begins again. The beer will never get to either of the temperature extremes, and in fact naturally wants to stay pretty stable. While extended periods of heating without normal cooling can be a problem, we are lucky that is not the norm in Southern California. Your results may vary in other regions of the world.

Whenever extended warm periods are likely it is wise to take precautionary action. The beer is most susceptible to the effects of high temperature when it is fermenting most rapidly. That means our main concerns only last for the 3 to 4 days of greatest activity. What to do? Cool adequately before pitching to avoid a hot start, pay attention to beer temperature during early fermentation, and as necessary employ evaporative cooling to keep the beer temperature from rising. Evaporative cooling is simply providing a wet covering for the fermenter surface so that water evaporation naturally cools that surface. Think of it as the fermenter sweating, or as a swamp cooler for the fermenter. It is most easily done by pulling a T-shirt over, or wrapping a wet towel around the fermenter. Placing the fermenter in a shallow tray will provide a water reservoir the fabric can wick to maintain the wet surface. With our normal low humidity, water will readily evaporate and cool quite effectively. High humidity regions may require air movement to help the cooling process, via oscillating fan or an open window.

If you haven't already done so, make certain to pick up an adhesive thermometers for each of your fermenters. They are inexpensive and will help you stay out of temperature trouble. You'll know at a glance if you should take action.