Wort Temperature During Fermentation
TroubleShooting
Jim Beyette - Ogdensburg, New York asks,
I have set aside a specific room for fermenting my beer. I have set up a heat-cool thermostat with heating and cooling to maintain an ambient temperature of 70° F as I am making only ales. My system is working fine — it controls room temperature perfectly. However, my fermentation temperature is at 74° F. I know this is true because I have a uni-tank-style fermenter with a thermometer in it. Does fermentation activity cause increased temperature, and if so should I compensate for it?
An active fermentation does create an appreciable amount of heat energy. In small fermenters where the ambient air temperature is used for cooling, there is always an increase in fermentation temperature as the brew goes into active fermentation. Most brewers compensate for this by setting the room temperature a little cooler than the desired fermentation temperature.
If you want to keep the beer around 70° F during fermentation, you may choose to cool the wort to 68° F and set your room temperature at 66° F. If you have healthy yeast, chances are that fermentation begins before your wort temperature drops down to the ambient temperature. As fermentation proceeds, the temperature will increase. When the wort gravity starts to tail off and fermentation slows, the temperature will begin to fall. Eventually the temperature will equalize with the ambient temperature. This is the “normal” temperature profile at most traditional breweries fermenting beer in small, oftentimes open, fermenting vessels.
Ale fermentations usually benefit from holding the beer at the fermentation temperature for a couple of days before cooling it down. This short hold is usually called the diacetyl rest since it allows the yeast to mop up diacetyl and convert it to odorless components. Cold aging your ale helps the yeast to flocculate and produce a clearer finished product. If you wanted to make lagers using ambient cooling you could do the same thing, but your room temperature would need to be cooler.
If you feel your beer is too fruity or is fermenting too quickly, you may want to cool your room down a few degrees. If you want a more vigorous ferment or more fruity flavors, try raising the temperature.
Incidentally, for those of you using carboys for fermenters, don’t feel left out of the fermentation-control game. Thermometers that stick to the outside of your carboy help with temperature control. You can also float a thermometer in your carboy or test samples.
