What does “cold crashing” mean?

Cold crashing is a topic that seems to have become hot lately with more and more mentions in social media groups about this catchy brewing term. Like many trending homebrewing topics, cold crashing is a term borrowed from craft brewing jargon.

Back in the old days when lager beers were aged in cold cellars stocked with ice during the winter, cooling from fermentation to cold lager temperatures took time because tanks were air cooled. Lager fermentation and aging practices changed following the advent of commercial cooling in that brewing was not limited to cooler months. However, lager tanks were still air cooled because tanks equipped with cooling jackets and coils had not yet been commercially used for brewing. In the days of air cooling, beer cooling was a slow process where tank temperatures typically dropped just 1–2 °F (0.5–1 °C) per day. This equated to 10–20 days between lager tank filling and arriving at the final lagering temperature. I am focused on lagers here because ale brewing historically did not include deep cooling.

Enter the modern era of brewing beginning in the middle of the last century when stainless steel tanks were first used, and cooling jackets became a common feature. The brewing process started to change where cooling efficiency improved and production times gradually shortened. Although established commercial breweries with cold lager cellars did not abandon their existing cellars, they did begin building fermenters with cooling jackets (as opposed to internal coils) and the use of beer chillers became increasingly common. Fast forward to today, brewers of all types typically cool to 28–34 °F (-2 to 1 °C) before clarification (if performed) and packaging.

Because all modern commercial tanks are equipped with cooling jackets, brewers can rapidly cool a tank from fermentation to cold-aging temperatures in 24–36 hours. Some brewers refer to this practice as deep cooling, because the beer becomes very cold, and others call it crash cooling because it occurs very quickly. “Cold crashing” is a smash up of both terms. What’s so special about this process? For the commercial brewers it’s all about time and money. In practice, however, some brewers prefer stepping down beer temperatures gradually because of concerns about off-flavors related to shocking yeast during rapid chilling. Whether this is a legitimate concern or not is a different question, but this concern means that not all brewers are in a race against the clock. Aside from time savings, I cannot find any data showing that rapid beer chilling improves beer quality versus slowly chilling to the same temperature.

That’s what cold crashing is, but what does it mean to the homebrewer? Unless special effort is taken to slowly reduce the set point of a refrigerator or a fermenter, cold crashing is going to happen at home because our batch sizes are small and cool very rapidly. Brülosophy did an Exbeeriment titled “Cold Crashing Speed: Immediate vs. Gradual in a Munich Helles” in 2020 indicating no sensory difference between the two test beers.

When I was a young brewer, we would say something like “transfer into a keg for secondary, toss the keg into the fridge after fermentation is complete and the pressure is where it needs to be for natural carbonation, wait long enough for the chunky stuff to settle, then enjoy.” These days, brewers say “pressure ferment your lagers, forget about secondary because that’s what dad did, cold crash it, and tap it.” To this grumpy old dude, looks to me like the same basic thing using a more modern name!