Homebrew Underground

When making ale, it is a good idea to wrap the fermenter with some wet towels (or a T-shirt) to keep it cool during fermentation. Fermentation tends to raise the temperature because heat is generated by the fermenting yeast. The principle of using wet towels or a T-shirt is like an evaporative cooler. When the water in the towels evaporates, it cools the towels, and the heat is transferred from the fermenter into the air via the wet towels. This can lower the temperature as much as 10 degrees below room temperature. The effect can be enhanced by blowing an electric fan on the fermenter.

Fermenting at too high a temperature will cause noticable off-flavors in the beer. It is most critical to establish a cool temperature within the first 8 hours to set a slow, even pace of fermentation. Off-flavors can occur at this time if the fermentation is too hot and too fast. You don’t want to slow down the start of fermentation, either, so it is best to wait about 5 to 6 hours after pitching the yeast to allow a quick start of the fermentation, then slow it down by cooling the fermenter. Keep it cool for the duration of the fermentation (about 4 to 8 days).

Ideally, you want the temperature of the wort to be 70° Farenheit when pitching the yeast. Also, if you are rehydrating dried yeast, it is a good idea to prime the yeast at the same temperature as the wort. The yeast will experience little or no shock this way and will stand the best chance of a rapid start of fermentation. When you pitch the yeast into the wort, aerate it thoroughly with a stainless steel whisk to bring oxygen into the wort. Yeast needs oxygen to get fermentation started.

It is best to keep the fermenter in a cool place during primary fermentation. Although the recommended fermentation temperature can vary depending on the brand of yeast, generally, the ideal fermentation temperature will be 60° F. During fermentation, the beer heats up, so even though you may have a room temperature at a chilly 70 degrees, the fermenting beer will tend to be hotter than the surrounding air.

Below is a shot of the fermenter with wet towels wrapped around it. The fermenter is placed in a tray filled with water and the towels are allowed to soak up the water. Wicking action causes the water will rise to the top of the towels and keep them wet. You can also cause the water to be cooler by placing ice in the tray. The melting ice will make cooler water. See the equipment page for a photo of the tray. The one I bought is called a "terra tray" or "Planterra Tray". It can be purchased from a local nursery supply or Home Depot.

It ain’t pretty … but it does the job!