What is cold crashing?
Cold crashing is the process of rapidly reducing the temperature of fermenting beer in order to produce a clearer final product. By reducing the temperature of the beer particles such as yeast, hops and other proteins clump together (flocculate) and fall to the bottom of the fermenter as sediment.
How to cold crash
The easiest way to achieve this is by turning down the temperature of the refrigerator or other fermentation chamber. The target temperature is around 37o Fahrenheit / 3o Celsius, just above the point of freezing.
Most of the activity takes place within the first few days but there are no issues with leaving the fermented beer at this temperature for longer.
Because of the need for extremely cold temperatures that are difficult to reach without refrigeration, the process of cold crashing is not possible for all homebrewers. If this is the case though, there are other options available as listed below.
When should you cold crash?
Cold crashing should be carried out only after fermentation has finished. Because the process of cooling the beer to such cold temperatures causes the yeast to go dormant it is important that fermentation has finished otherwise your beer may not reach the desired final gravity or alcohol level.
More importantly though, if the yeast has not finished fermenting, there will still be unfermented sugar in your beer. This means that when additional sugar is added at bottling time there is an increased chance of ‘bottle bombs’ when the beer is allowed to return to room temperature for carbonation.
The effect of cold crashing on fermentation
As mentioned above, the process of cold crashing involves reducing your beer to temperatures below that which the yeast are able to remain active. The result of this is that the fermentation process will stop while the yeast remain dormant.
Although the act of cold crashing will cause some of the yeast to sink to the bottom, enough will remain to complete the process of carbonation following bottling. Because there will be less yeast in the bottle though, carbonation will often take longer – This may stretch the time required for carbonation up to 3 or 4 weeks.
Alternative ways to clear beer
Cold crashing your homebrew is something that will work to produce clearer beer by itself but will also work with most of the traditional brewing additives that are used for the same purpose. These include the addition of things such as Irish moss or Whirlfloc tablets during the boil or ‘finings’ (such as gelatin or Isinglass) to the fermenter. These additives also work by encouraging unwanted elements like yeast and proteins suspended in the beer to clump together and fall to the bottom of the fermenter.
Photo by RachelEllen