Fermentation Temperature: A Key Part Of Making Beer

If there is a single issue that dooms most home brewers, it is fermentation temperature. Beer fermented at the proper temperature has a great flavor, while beer fermented either too cold or too hot tends to taste “off.” Worse yet, incorrect fermentation temperatures can stop the fermentation process entirely, ruining the entire batch of beer.

Particularly when brewing beer in the summer, or in warmer climates, many home brewers start the fermentation process at a high temperature. This can lead to many flavor issues or even ruin the whole brewing process.

Beer that is fermented at higher temperatures tends to pick up bad flavors from esters and fusel alcohols produced by the yeast. High temperatures can also cause the yeast to consume nutrients too quickly and run out of fuel before finishing off the sugar, which leaves the fermentation process incomplete.

Heat stress can kill off yeast directly, causing the remaining yeast to overwork and produce bad flavors, or limit the yeast’s alcohol tolerance, which again results in incomplete fermentation. It is important to note that the fermentation process itself produces heat, so starting fermentation with the temperature too high can cause the heat to spiral out of control.

Winter is the traditional time to brew beer because the cold helps prevent spoilage. There are fewer bacteria and wild yeast to interfere with the process. Nevertheless, starting the fermentation process too cold can lead to another set of problems.

The fermentation process requires some degree of heat to get started. Cold temperatures can make it so the fermentation never starts, or can cause fermentation to proceed slowly, dragging on for weeks and eventually coming to a stop. This leaves the would-be brewer with unfermented or incompletely fermented beer.

Even if fermentation does take place, cold temperatures can wreak havoc on the beer’s intended flavor. Some ales require a fruity flavor; fermenting too cold can leave the flavor clean, bland and inappropriate for the style. Cold can also cause carbon dioxide to become entrained in the beer, which keeps unpleasant flavors that would normally leave the beer in a gas to make it to the final product.

The final risk of fermenting at cold temperatures is contamination. The cold kills off many bacteria, but if contaminants still make it into the batch the cold also slows down yeast and gives those bacteria a chance to take over. Those bacteria can ruin the entire batch of beer.

With all these risks, it is obvious that temperature control is absolutely critical. First, the brewer needs to find out what the temperature is. The best way to accomplish this is with a separate thermowell containing a temperature probe, which gives the most accurate temperature reading possible.

Many brewers use thermometers to keep tabs on the fermentation temperature. Stick-on thermometers can work, but liquid-filled thermometers tend to give a more accurate reading. It is also important to bear in mind that the temperature of the brewing wort may be different from the ambient temperature inside the refrigerator.

Finally, the brewer must take steps to control the brewing temperature. One way to accomplish this is with an analog temperature controller, which sets the temperature inside a refrigerator or freezer by bypassing the internal thermostat. A more reliable, albeit more expensive option is a digital electronic thermostat control.

Other brewers use FermWraps to directly control the temperature inside the batch, or rely on old-fashioned solutions such as ice baths and evaporation-based cooling. No matter which method is used, proper temperature control is the key to making a great batch of homebrew beer.