Fermentation Temperature Control

Fermentation temperature control is the single most important thing you can do that will make the most dramatic improvements in your beer. And it can be a big problem, especially when brewing in the Deep South. Winter brewing is great but summer brewing can be brutal in the 100°+ days. Without temperature control, it’s simply impossible to brew most beers correctly. Many homebrewers underestimate its importance and therefore are doomed to brew mediocre beers.

What Happens if Your Fermentation Temperature is Too Warm

• The biggest problem is the off flavors from esters and fusel alcohols that the yeast produce. Sometimes the flavors are not so much “off” as they are inappropriate for the style.

• Your yeast can blast out of the starting gate, consuming everything in sight, then run out of nutrients before finishing the sugar. This usually ends in an incomplete fermentation.

• Poor fermentation temperature control often results in fermentations that are too hot, causing the yeast to become too sensitive to alcohol toxicity (meaning that they will die off from the alcohol before their usual tolerance is met).

• Yeast begin to die off from heat stress, leaving the remaining yeast to do all the work. In effect you ended up under-pitching the yeast and will get off flavors as a result.

• Since yeast metabolism generates a lot of heat, starting fermentation at too high of a temperature will quickly lead to problems as the temperature will climb in the 80°F+ range and yeast die off.

What Happens if Your Fermentation Temperature is Too Cold

When brewing in colder climates or during the winter without temperature control, yeast will exhibit stress problems too. Winter is the traditional time to brew because there is less spoilage bacteria and wild yeast to contend with.

• Your fermentation may never get started.

• Your fermentation may be sluggish and drag on for weeks before finally getting stuck.

• For ales that require a degree of fruitiness from esters, fermenting too cold can lead to a beer that is too clean or bland for the style. Judges will be looking for flavors and aromas that just didn’t make it into the beer due to the cold fermentation.

• If there is any contamination in your beer, it is going to be a race to see which can dominate the fermentation. A sluggish start from poor temperature control can give these bacteria a chance to take over and ruin a batch of beer.

• When fermentation does commence in an environment that is too cold, CO2 becomes entrained in the cold beer. Flavors that are normally “gassed off” stay in solution and may make it through the entire fermentation process to the final product. This is especially true for the “sulphur” aromas and flavors produced in lager fermentations.

DEGONG beer fermentation tank