Optimal Temperature in Fermentation

The Importance of
Temperature in Fermentation

Accurate temperature during fermentation is crucial for brewing reliable, good beer.  Yeast requires the right temperature to ensure healthy fermentation; Too warm, the yeast will get stressed out. Too cold, the yeast will be sluggish and not as active.

What happens when fermentation temperature is too warm?

1. Nasty B.O. (Beer odor)
When yeast has to work in environments that are too hot, they start to produce foul aromas, similar to the smelly, sweaty results of exercising outside on a hot day as opposed to an air conditioned gym. The fermentation rate accelerates as temperature increases, which produces more aromatic compounds due to the excretion of metabolic intermediates from the yeast cells. Esters, a class of fruity aromas reminiscent of pineapple, banana, and pear, are associated with warm fermentation.  Some esters, like ethyl acetate, can smell like nail polish remover or solvent.

2. Desirable Aromas Blow Off
When the fermentation temperature gets too hot, yeast becomes stressed and desirable hop, malt, and fruit aromatics blow off.

3. Sulfur Smell
Stressed yeast results in elevated hydrogen sulfide, which can make your beer smell like sulfur.

4. Yeast death 
Increased temperature leads to increased cell wall permeability to alcohol, producing a toxic environment for yeast.

5. Higher alcohol 
Increased heat also increases the production of higher alcohols.

What happens when fermentation is too cold?

1. Sluggish, Sleepy Yeast
Most yeast strains will become sluggish in colder temperatures during fermentation. Some will completely shut down and hang in clumps at the bottom of the fermenter.

2. Longer Fermentation Time
Yeast will struggle to work in cooler temperatures during fermentation.  This will also increase fermentation time.

While some styles of beer, like lager, require cooler fermentation temperatures to create a clean, crisp beer, most styles will be hindered in cooler temperatures.

The ideal temperature for most yeast strains is between 60-80F degrees.  Each yeast strain is different, so the ideal fermentation temperature varies. It’s a good idea to check the recommended temps from the yeast manufacturer you choose.



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