Soft Crashing for Clarity

We talk a lot about existing techniques and new innovations for haze a lot. But what about the clearer side of brewing? In terms of fundamentals for achieving crystal-clear beer, soft crashing is a useful technique.

After the diacetyl rest, instead of immediately dropping the temperature all the way down to your final crash temperature, a soft crash can be performed, which could involve one of a few approaches: you could cool to an intermediate temperature and hold it for 12 – 24 hours before cold crashing. Or you could slowly lower the temperature by a few degrees at a time over an even longer period of time (like 24 – 48 hours) before cold-crashing.

The theory behind this approach is that the yeast needs time to express the genes necessary for flocculation. Each yeast strain is encoded with specific genetic information that specifies their ability to flocculate.

Once the yeast cells are cold, their ability to express those genes is significantly diminished. By giving them a transitional period at a slightly warmer temperature, you allow them to prepare for the final cold lagering stage, leading to better yeast flocculation and, ultimately, clearer beer. This technique isn’t limited to lager brewing. Soft crashing can help clear up ales, too.

Many brewers use a soft crash to encourage a more successful yeast harvest for repitching, but it is also a common practice to soft crash before dry hopping. Some prefer the overall impacts on hop aroma and flavor, and others use it as a method to mitigate dry hop creep: by lowering temperatures during dry hop, you reduce how much refermentation happens or can happen.

Here’s how to incorporate the soft crash into your brewing process:

• Post-VDK rest. After completing the diacetyl rest, where you allow the yeast to clean up any unwanted byproducts, begin the soft crash.

• Cool. Lower the temperature below that of your diacetyl rest by about 5 ‑10 degrees (Fahrenheit). Your target temperature varies based on whether you are fermenting with an ale strain, which would likely be between 65 – 72°F or 18 – 22°C, or a lager, which would likely end up between about 50 – 60°F (or 10 – 15°C). Aim for a temperature between 45 – 60°F (or 7 – 15°C) for your soft crash, and experiment from there.

• Hold. Lower temp incrementally over several days — or achieve your soft-crash target temp right away, and just maintain it for 12 – 24 hours.

• Lager. For lagers, slowly continue to decrease the temperature to your desired final lagering temperature, which depends on your process and strain.

Non-flocculant yeast can add to production time. If you don’t give the yeast sufficient time to flocculate in the cellar, then the yeast will eventually settle in the package. For some beers this is acceptable (think of the swirl and pour method for a German Hefeweizen), but it can also lead to off flavors from autolysis, or very sluggy pours from draft beers as the yeast settles in the keg.

Implementing this technique can make a substantial difference in the clarity of your beer. It can improve flocculation and lead to a final product with improved clarity. By adopting this technique, you can enhance the consistency of your beers and achieve the crystal-clear results you’re working towards. 

Saison strains, lager strains or less flocculant strains will benefit more. A highly flocculant strain like Extra Special, for example, wouldn’t benefit as much from this approach because it is already practically cemented to the bottom of the tank at the end of fermentation.

Here’s a helpful illustration of the process in a basic lager style: