Good temperature control is one of the most effective ways to improve the quality of your homebrew. It’s what elevates great beer above good beer. In fact, the ability to select and maintain the temperature of a fermentation is probably the single greatest technical advantage that professional brewers enjoy over homebrewers.
Good temperature control ensures that fermentation remains within the range of conditions best suited for your yeast of choice. This might be as high as 70–80°F (21–27°C) for Belgian ales or as low as 45–55°F (7–13°C) for German lagers. Here are a few ideas, roughly in order from least to most effective (and, correspondingly, least to most expensive) for keeping your cool.
If you don’t mind brewing seasonally, then you can take advantage of your home’s natural temperature variations. You probably won’t be able to make lagers, but it should be fairly easy to brew British ales in winter and saisons in summer. This is how brewers did it before the advent of air conditioning, and many of us still brew this way at least some of the time.
Feasible temperature change: None.
A cheap but effective option (especially for brewers who live in dry climates), an evaporative cooling scheme operates on the same heat transfer principles as a swamp cooler. Simply place your fermentor in a tub of cool water and cover with a damp shirt, towel, or blanket, making sure that the damp cloth touches the water. Point a fan at the setup, and the water will naturally carry away heat as it wicks up the cloth and evaporates.
Feasible temperature change: 5–10°F (2.8–5.6°C) below room temperature.
Temperature-Controlled Chest Freezer or Refrigerator
For most homebrewers, this option offers the best balance of precision and cost. If you have an old refrigerator or freezer, you can purchase or build an external controller with a probe that is placed inside the chamber. You plug the fridge or freezer into the controller, plug the controller into an outlet, and set the controller to your desired temperature. When the probe indicates that the internal temperature has exceeded the setpoint, the controller delivers power and the compressor kicks in to lower the temperature.
Feasible temperature change: Anywhere from freezing up to room temperature.
Jacketed Conical Fermentor
If you really want to brew like the pros and can afford to spend the money, then a homebrew-sized conical fermentor is the way to go. The most advanced models offer both heating and cooling mechanisms and will maintain fermentation to within 1° F (0.6° C) of the desired temperature. Some even allow you to program an entire fermentation profile that varies with time.
Feasible temperature change: Whatever you want.
There are certain circumstances in which you may want to raise fermentation temperature, and in "Keep it Warm," we review ways to do just that.