What is the most basic and critical factor that drives the fermentation of your beer? Obviously, the yeast. Did you realize, though, that the temperature at which fermentation occurs will dramatically affect the flavor of your beer?
Each yeast strain has a narrow range of temperatures at which the ideal fermentation will occur. Too warm, off-flavors will be formed in the beer. Too cold, fermentation will not be vigorous enough to complete.
When I started home brewing beer I was letting it ferment in the hallway of an apartment without air conditioning, in the middle of summer, at temperatures of 80 to 85 degrees. I did not realize at the time that this is what was causing my beer to have some funky off-flavors.
The ideal fermentation temperature for most types of ale yeast is in the mid-60’s Fahrenheit (lager yeasts like it cooler). In many areas it is difficult to keep fermenting beer at this temperature because it is too hot in the summer or too cold in the winter.
Even with forced air heating or cooling your house, there is likely to be a several-degree swing in temperature
There are some tricks that can be used to help the beer ferment at a steadier temperature, though:
Keeping Beer Warm Enough
If you have to ferment you beer in a basement or garage in the winter (I’ve even had difficulties in an unused spare bedroom in the winter) you likely will not have the sufficiently warm 65 degree ambient air temperature that you need.
A simple way to keep your fermentor warm enough (if you are fermenting in a carboy, rather than a bucket) is a carboy parka
. These come in many different variations, but they are always a fitted cover that is meant to provide insulation to reduce temperature fluctuations.
These work especially well because the process of fermentation will naturally heat up the vessel, in some cases as much as ten or fifteen degrees, and the parka will keep this warmth in. Carboy parkas also have the benefit of blocking out harmful UV rays from the beer.
Some carboy parkas are really basic, and some nicer ones (like the one pictured below) are made of a more insulated material and come with handles for moving the carboy easily.
Electric Carboy Parka with Handles
Electric Carboy Heaters
If a carboy parka just isn’t enough to keep your beer up to fermentation temperature then an electric carboy heater
(like the one pictured below) is the way to go. These are simply electric heater pads that hook up to a temperature controller
to keep your beer at a very specific temperature. They can be used on glass, plastic, and metal fermentors.There is not any guessing involved about the temperature, like there might be with a carboy parka. Electric carboy heaters will keep your fermentor warm enough no matter the conditions.
Electric Carboy Heater
Keeping Beer Cool Enough
The most basic method of keeping a fermentation vessel cool enough in hot temperatures is commonly referred to as a “swamp cooler.” This term refers to keeping the fermentation vessel in a tub
of water filled up at least to the level of the beer in the fermentor. Since water is more resistant to temperature change than air, it will not heat up as quickly or cool off as quickly as the air in the room. A floating thermometer
can be placed in the swamp cooler, or an adhesive thermometer label called a Fermometer
can be placed on the outside of the fermentation vessel to monitor temperature.
Even outside of avoiding temperature extremes, it is easier to control the temperature of the fermentation when the fermentor is surrounded by water. If the water is too warm it is easy to add ice or a frozen bottle of water to cool it off. It is even possible to set up a pump to circulate water from a tub of ice water into the swamp cooler. The pump can be activated by a temperature probe
if the water in the swamp cooler gets above a specified temperature .
If it is difficult to keep the fermentor cool enough you can also wrap it in a towel, with just the bottom of the towel touching the swamp cooler water. The towel will wick water up to cover the fermentor, and as the water evaporates away it will naturally cool the fermentor. For an added boost to the cooling, place a fan nearby and have it blow past the vessel to encourage more rapid evaporation.
If the water in the swamp cooler gets too cold, an aquarium heater
can be dropped in to heat it up.
Swamp coolers are a great option if you are looking for a way to automate temperature control without committing a lot of money or space to a converted chest freezer (see fermentation chambers, below).
Fermentation Cooler Bags
A simple alternative to swamp coolers are Fermentation Cooler Bags, like this one
, that are essentially the cooling version of a carboy parka.
Cooler bags are made of heavy-duty insulated material into which you place your fermentor and bottles of frozen water. Each one-liter bottle of ice will typically cool the fermentation temperature by about five degrees Fahrenheit, down to about 30 degrees below the ambient room temperature.
Fermentation Cooler Bag
A more sophisticated method of stabilizing fermentation temperature is to build a fermentation chamber.
Most fermentation chambers are built from an insulated container such as an old refrigerator or freezer. A temperature controller
is used to regulate the temperature of the chamber. If the chamber is kept in a cold area, such as a garage, a heater may actually have to be placed in the chamber to keep it from getting too cold.
Monitoring the temperature of your wort in a fermentation chamber is a little more tricky than doing so in a swamp cooler. The wort will heat up and cool down more slowly than the air in the chamber, so to obtain a more accurate reading you need to either add a temperature probe
to the wort, or add a probe to a container of water that is also in the chamber to mimic the wort temperature.
A nice piece of equipment that will help regulate your fermentation chamber is a switch
that can be activated by a temperature probe. When the temperature in the chamber falls outside of the specified range the switch will activate either the refrigerator or the heater as necessary.
Have you tried any other methods of controlling fermentation temperature? Tell us how they worked for you in the comments below!
Note: For you to reference, we do our best to link to versions of the items that are mentioned in our posts that are sold by home brewing stores (or the direct supplier) via Amazon, which is a familiar and comfortable site for most users. We do receive a small commission for any purchases that you make via Amazon, at no extra cost to you, which helps to support the upkeep of this site.