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According to "How to Brew" by John Palmer (4th ed.), cold conditioning (a.k.a. lagering) is the act of cooling beer after fermentation has completed (including maturation) in order to clarify the beer. So far so good.

The book also suggests to slowly decrease the temperature (down to 1 °C/day!) to avoid thermal shock on the yeast:

The point of slow cooling is to prevent thermal shock of the yeast and subsequent excretion of fatty acids and other lipids. These lipids can interfere with head retention and will readily oxidize, creating stale flavors. Thermal shock at any time can cause the yeast cells to release protein signals that cause other yeast cells to shut down to protect against the cold, potentially leading to premature flocculation and underattenuation.

However, everyone seems to cold crash, and I did not find other sources supporting this claim. Is there any evidence? Am I missing something?

I am also not sure whether this would also be relevant for pitching temperature since, for instance, the rehydration temperature for dry yeast is usually higher than fermentation temperature.

... last but not least, such method definitely makes the overall process 1-2 weeks longer, which is pretty annoying.

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I send an email to John Palmer, he has been kind enough to answer. I guess it is ok to post it here, so here it is:

Hi,

It's best practice. Lots of breweries cold crash, and they lose head retention as a result. Thermal shock is most prevalent on cooling, not heating, although it can occur then too. But the difference of 10-20F at pitching doesn't have the mass effect as 30-40F after fermentation when you have 4X as much yeast.

John

For the Celsius side of the world, a difference of 10-20 °F amounts to 6-11 °C, while a difference of 30-40 °F is 17-22 °C (I did some rounding).

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I have never noticed a problem with cold crashing. In reality, it takes a while for the temperature to drop anyway (albeit not 1*C per day). If you are hoping to harvest the yeast, shocking them unduly could cause you issues, but otherwise, I would say crash away. If, in the future, you come across an issue that could be explained by insufficient yeast during lagering, and you've ruled everything else out, try using the slow approach to see if it fixes the problem. Otherwise, you should be right.

  • Thanks for reporting your experience. In the end, I got an answer from the book author directly, which I posted here. – effeffe Jul 3 '19 at 12:51

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