Temperature has a big impact on how yeast ferment. In fact, it can even prevent yeast from fermenting. Pasteurization is the extreme example on the hot side that can kill yeast. Cold can also prevent or slow yeast strains from fermenting but, it doesn’t tend to kill the yeast. Freezing the yeast won’t necessarily kill it. The standard yeast for brewing and wine making is Saccharomyces cerevisiae. By default, this yeast is often used for hard cider making as well. Saccharomyces cerevisiae generally prefers temperatures around 20C (68F) and this temperature has become a standard target to ensure complete fermentation. Non-Saccharomyces yeasts, like those naturally found on apples and used in wild fermentations are usually more cryotolerant. Does that mean you should ferment cold or hot?
All yeast have temperature limits where they will stop fermenting or even die. However, the temperature range is usually about how well they ferment. This temperature range for commercial yeast strains is set not because the yeast won’t ferment beyond that range but because the aromas they create tend to be less desirable beyond that range. It can also impact the fermentation rate. Generally, the colder the temperature, the slower the fermentation rate. The hotter the temperature, the faster or more aggressive the rate of fermentation will be. Temperature also changes the aromas a yeast will produce. Yeast fermented cold tend to produce fruiter esters while warmer temperatures tend to produce more phenolic esters. Hotter also tends to produce more esters but since hotter is more aggressive and esters are volatile compounds, hotter fermentations tend to also lose more esters. Hotter fermentations also extract more phenolic compounds. This is why red wine is generally fermented hotter than white wine. When adding apple peels to your primary, hotter temperatures will help draw out more of the phenolic compounds.
All of this shows that like almost everything with cider making, there are always trade-offs. It also highlights the need to experiment and not accept standard practices of either fermenting hot or cold. So, enjoy experimenting and try fermenting at warm and cold temperatures and to assess the change. That is what I did with my Winter Cider.
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