Techniques for Managing Temperature
After proper yeast management, temperature control brings the biggest boost in beer quality. Even warm fermenting ales need cooler temperatures than the average room temperature.
Fermenting warm does a number of things to the brew. Yeasts produce more esters and fusel alcohols when hot. Fusels are solvent-smelling higher alcohols that lead to nasty headaches. Most yeast produce an overabundance of aromas like diacetyl, sulfur, cooked corn, and so on, while eating too much sugar. It's not a pretty picture.
Hefeweizen strains are the classic example of dramatically changing yeasts. Fermented cool, they generate clove phenols. As they ferment warmer, the clove disappears, replaced by banana and then bubblegum.
Spoilage increases with heat. Traditionally, summer brewing was forbidden for this very reason. Even with an adequate yeast population, spoilage bacteria can leave a mark on your brew.
Monitor the temperature span experienced by the wort. During the course of the fermentation cycle, you want to keep the beer from swinging more than 10°F. Large thermal shifts can shock the yeast cells and cause them to go dormant. Fermenting in an uninsulated garage, for instance, requires a close eye on the needle.
Following are some recommended methods for cooling and heating;
Evaporative cooling — The cheapest and easiest-to-implement suggestion. Find a large, shallow pan. Slip a T-shirt over the fermenter and set it down in the pan. Fill the pan with water and wet the T-shirt. As the water evaporates from the shirt, more wicks up from the pan lowering temperatures by a few degrees. Point a fan at the assembly to speed up the effect. Useful for cooling a fermenter in an air conditioned room.
Water bath — Fill a clean trashcan with water and ice to cover the fer-menter. Add new ice periodically. Leave a floating thermometer in the bath to check the temperature. To save on ice, freeze water-filled soda bottles. Put two two-litter bottles in the bucket every twelve hours to maintain temperatures.
Fermentation chiller — For craftsmen, look online for the Son of Fermentation Chiller. Using thick polystyrene walls, the SoFC is an ice-powered fermentation chamber. The chiller monitors the temperature in the chamber and blows cold air to keep the temperature down.
Refrigerator/Freezer — Lagers need colder temperatures. An external thermostat-controlled refrigerator or freezer is a powerful fermentation chamber. Set the temperature and your fermenters quietly rock away at the right temperature.
Brewers in northerly climes have the opposite problem. How do you keep the fermenter chugging at 68°F when the wind is howling below 0°F?
Brewbelt — An electrically heated band the circles a bucket and heats a narrow region of the brew. Cheap and effective.
FermenWrap — A flat-panel heater designed to wrap around a large fermenter. With an external thermostat it can provide heat when needed.
Light bulb — Placed in a refrigerator, an incandescent light bulb keeps a fermenter snug. With a two-stage thermostat, a brewer can set up a year-round fermentation chamber.