Homebrew School: What Is Cold Crashing?

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.

What is Cold Crashing?

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°C as possible - usually around 3°C. This is typically done by having the fermenter situated in a refrigerator, but can also be accomplished by having a glycol chilling system connected.

Benefits of Cold Crashing?

• Improved Beer Clarity: 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.

• Enhanced Flavour: Less yeast in the remaining beer can lead to improved flavour in some cases.

• Hop Matter Reduction: 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.

• Krausen Breakdown: 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.

• Rapid Carbonation: 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.

• Less Sediment in Bottles: If you are bottle conditioning, you will notice less sediment in the bottom of each bottle after conditioning.

Cold Crashing can leave clearer beer at the top and more sediment in the trub cone

Disadvantages and Risks of Cold Crashing?

While cold crashing has its benefits, there are some potential disadvantages and risks:

• Vacuum Effect: 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).

• Equipment Requirements: You need a fridge or other specialised equipment to perform this (like a glycol chiller), 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 fermenting yeast get too cold and the temperature of the wort 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.

Cold Crashing our Keg King Apollo Titan fermenter in our fermentation fridge

Is it Worthwhile Performing 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.

Stepped Cold Crash

Another new concept in the brewing game is the belief that a cold crash can cause yeast to excrete lipids and other compounds that can have a negative impact on foam stability in the finished beer (causing the foamy head of your beer to collapse sooner in the glass).

The Brulosophy Show ran an Exbeeriment on this with an American IPA and the results were certainly interesting, though this obviously only represents a single data point, so not necessarily a conclusive result.

Based on this, we have been implementing a stepped cold crash into our end of fermentation routine, and have a noticed a slight increase in head retention, though this is just based on our own anecdotal evidence and nothing thoroughly documented.

In our case, rather than setting our temperature controller to 0°C and letting the fermentation fridge cool continuously until it won't get any colder, we drop the target temperature of the fermenter 2°C every 12 hours until we reach our desired temperature of around 3°C.

In our opinion it's certainly worth considering if you have the ability (and patience) to do so to see if you notice any difference yourself.

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