Cold Crashing is a really common term and process used by home brewers. No doubt if you're a new brewer you've probably come across the term in homebrew user groups and other articles and are wondering what it means.
The term "Cold Crashing" refers to the process of rapidly dropping the temperature of your recently fermented wort - which is now beer whilst it is still in the fermenter. The desired temperature is typically as cold or as close to 0 as possible - usually around 3 degrees Celsius. This is typically done by having the fermenter situated in a refrigerator, but can also be accomplished by having a glycol chilling system connected.
What are the benefits of cold crashing?
- It helps some of the remaining yeast in the beer flocculate or clump together and then drop to the bottom of the fermenter into the trub pile which can help to improve beer clarity and reduce the chances of particulates clogging lines, disconnects, bottling wands etc during the packaging process.
- Less yeast in the remaining beer can lead to improved flavour in some cases.
- If you have added dry hops to your fermenter, it also helps any remaining hop matter floating on the top of your beer to drop to the trub pile at the bottom of the fermenter.
- If you have some stubborn krausen that is still remaining on top of the beer, a cold crash will help it break down and settle to the trub pile as well.
- If cold crashing in a pressure capable fermenter, you can apply CO2 gas pressure to the headspace of the fermenter which will be absorbed into the beer more rapidly as the temperature drops which can give you a head start on carbonation, or even give you a fully carbonated beer by the time the cold crash is finished.
- If you are bottle conditioning, you will notice less sediment in the bottom of each bottle after conditioning.
Are there any disadvantages or risks with cold crashing?
- The rapid drop in temperature will cause a vacuum or "suck back" effect that can have several impacts. If you are using an air lock with sanitiser in it on your fermenter, the sanitising solution can be sucked into the fermenter/beer. If the fermenter is airtight, this can potentially cause the fermenter to collapse in on itself due to the negative pressure that is created by the temperature drop. If the fermenter is not airtight, then some oxygen/air may be sucked into the fermenter and potentially absorbed into the beer (though the impact of this last point is still widely debated).
- You need a fridge or other specialised equipment to perform this, which is not accessible to every homebrewer. Or an incredibly cold climate.
Can you still bottle condition after cold crashing?
We pondered this one ourselves when we first started cold crashing - as to whether there would be enough yeast left in suspension for bottle conditioning after cold crashing? The answer is definitely "yes". We've bottle conditioned multiple beers after a cold crash and had no issues with the remaining yeast providing adequate carbonation by consuming whatever additional fermentable sugar is added at bottling time.
Does cold crashing stop fermentation?
Performing a cold crash will essentially put a "pause" on fermentation if fermentation is still active when you begin a cold crash. If the yeast that are fermenting get too cold and the temperature of the wort they're fermenting in drops below their operating range, they don't die, but rather become dormant or inactive. This will lead to fermentation slowing to a stop, but should not be used to a method to finalise or finish fermentation early. Doing this will leave fermentable sugars in the wort, and the remaining yeast will continue with fermentation when the temperature of the beer/wort is raised again which can be dangerous, especially if you are planning on bottle conditioning.
Always wait until fermentation has completely finished before initiating a cold crash.
Is it worthwhile doing a cold crash?
In our opinion if you have the ability to perform a cold crash then it is definitely beneficial to do so. Yes, there is a risk of oxidation however this is quite possible an old wives tale. Brulosophy ran an exBeeriment testing this very thing which essentially debunked it.
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