Fermentation is greatly dependent on temperature, cold can interfere with it and it’s important to pay attention to what temperature the yeast strain that is being used demands.
It’s possible to get away with fermenting in a cold room with certain yeast types while others will be obliterated by the cold and you won’t be happy with the results.
So, what could happen if you ferment beer too cold?
If it’s too cold for beer fermentation, the yeast will become sluggish so it will take longer for fermentation to complete, the off-tastes may occur and the yeast could go dormant. Temperature is crucial for a homebrew beer to end up good, so control the temperature at all times until the fermentation is complete.
Can yeast die from cold?
Yeast won’t die from being exposed to cold but it will go dormant if the temperature is too cold for that particular yeast strain.
It’s possible to warm up the fermenter as the yeast will soon activate when it’s warmed up. Yeast is a resilient creature so it won’t die in the presence of the cold but rather take a nap.
However, it’s possible to shock yeast by putting it in cold and warm over and over again, especially for a short period of time. As resilient as the yeast is, it’s still possible to hurt it so be careful and don’t quickly drop and increase the temperature in order to give it some room to breathe and adapt to temperature change.
If you worry about the potential risks of a stressed yeast, you have a good reason to worry as stressed yeast can come with terrible consequences.
Bear in mind that yeast is more likely to die from heat exposure than from cold. Thus, be careful never to exceed the temperature above the point the yeast can handle. This mistake sometimes happens during pitching if the wort hasn’t cooled to an optimal temperature. Remember, it’s better to pitch yeast a bit later when everything is ready than to force it.
How cold is too cold for beer fermentation?
Fermentation temperature is always dictated by the yeast used, so it’s important to understand the temperature range of the yeast you plan to use in advance.
| Yeast type | Possible Fermentation temperature | Too cold to ferment |
|---|---|---|
| Ale Yeast | 59°F – 78°F (15°C – 25°C) | 55°F and below |
| Lager Yeast | 45°F – 55°F (7°C – 13°C) | 40°F and below |
It’s important to never go below the yeast’s temperature range or it will go dormant and fermentation will stop. It’s also important to keep the fermentation at a stable temperature, so ideally you don’t want big oscillation (greater than a degree up or down).
Furthermore, the possible fermentation temperature in the table above suggests the possible range in which yeast types can ferment, however, the optimal range that will produce desired results depends on from yeast to yeast. (Not all ale or lager-type yeasts produce the same results at a given temperature, but can ferment at)
Why does fermentation temperature matter?
Without good temperature control, there’s no good beer. Temperature is among the critical factors in brewing and it’s worth paying special attention that fermenting temperature stays stable.
Every yeast produces different flavors and aromas depending on the temperature, so when you ferment at the lower part of the range you may expect totally different yeast characteristics than you would if you fermented the same yeast at the higher part of the temperature range.
Going below the acceptable range will put the yeast to sleep and fermenting above the acceptable range will create terrible off-flavors such as fruity esters and harsh alcohol flavor. Going all the way above 86°F (30°C) may kill the yeast and make fermentation impossible.
There’s also the optimal range every yeast has and that’s somewhere in the middle of the range the yeast can ferment within. The optimal range is either suggested by the manufacturer or by homebrewers who experimented and figured out what’s the best environment for the yeast in certain recipes.
You can also use the same yeast but ferment it at different temperatures for different recipes to achieve what the recipe calls for.
Tips for having a successful fermentation
Use high-quality fermenter
Not every bucket is good enough for fermentation, so use a fermenter manufactured for home brewing. You can ferment in plastic, glass, or steel fermenter and each fermenter has its pros and cons. However, some factors can be critical such as how easy is it to clean and sanitize the fermenter from the inside or how well it conducts heat. Also never ferment in a non-food-safe material.
Pitch at the correct time
It’s dangerous to pitch yeast while the wort is still hot, so you need to wait for the correct time. You can cool wort with chilling methods, but very often it takes quite some time and effort before the temperature is right.
Remaining calm and patient is an important trait because pitching while the wort is too hot can seriously damage the yeast colonies and reduce the fermentation quality. I like to wait before pitching until the wort reaches the upper point on the temperature scale the yeast can ferment within.
Control temperature
Temperature control begins with pitching and is important throughout the entire fermentation process until the fermentation is complete. Usually, the very first 3 days matter the most and that’s when the stable temperature is most important as that’s when yeast adapts and does most of the work. In the remaining days, temperature control is still important but as the fermentation completes it plays a lesser factor.
If you find it difficult to control fermenting temperature, I have shown in the mentioned article how I deal with unpredictable temperature spikes.
It’s also not unusual to recommend slightly increasing the temperature by a few degrees when the fermentation is at 90%+ to being complete as it can provide the warm finish and extract the minimal amount of esters and alcohol aromas by the end which can benefit the recipe. However, such practices are not important for all recipes and won’t necessarily make or break the beer.
Give it enough time
Just as is the case with anything in life, it’s important to give fermentation enough time. Some yeast like Safe Ale S-04 will ferment a light ABV beer in 3 days, while Safe Ale S-05 or some other yeast may take 5 days or more. Lager yeasts can take weeks to complete and so on. It’s recommended to keep the beer in the primary for some extra time after you suspect the beer is finished fermenting just to be sure and to let things settle down and condition a bit while there’s still plenty of sediment in the fermenter.