What is the highest degree of temperature reduction yeast can tolerate, on a 24 hour basis?
We have a Festbier that just went through a D-Rest at 64 F, and now it is time to cold-crash the brew. The goal is 32 degrees.
I did read that too rapid a temperature reduction can cause off flavors.
What say you?
I guess it is a question of how quickly the fermented beer actually drops to just about freezing. I have never experienced problems from cold crashing, but my fermentation fridge can’t move the needle all that quickly. I get there over 2 days or so, which is not problematic, as my yeast will roar to life on repitching within a week or so of the racking from a cold crashed fermenter. I take that to indicate that the yeast is healthy. That and not experiencing off flavors are my confirmation that the process is working….
I have talked to pro brewers who take a couple to four days to drop the finished beer to lagering temperatures, but they have much more control over the rate of drop using glycol.
Also, for what it is worth, I find the D-rest to be largely unnecessary with most healthy pitches of lager slurry. Cheers and YMMV, of course.
In the case of cold crashing, Palmer has told me that too rapid a reduction of temp will cause yeast cells to release lipids which can have a negative effect on foam. Being me, I ignored him and did it anyway. I didn’t detect any problems. Sometimes reality astonishes theory.
Same with me. I cold crash in a chest freezer and it takes at least a day-plus to reach the final cold temp. But where I worked, we did not step down the temp for cold crashing. We went from ferm temp to ~30 degrees in one step, and it didn’t take long. Never an off flavor, never head issues.
I have always put this “fact” in the category of “brewing myth that has been handed down over the years by well-meaning but incorrect people who think they know more about yeast biology than they really do.”
And it doesn’t even make sense. After all, if you can take yeast out of the fridge and immediately pitch it, why would it suddenly freak out going in the reverse direction? And I have received plenty of room-temp liquid yeast packets over the years…and they immediately go in the fridge when I open the box. And yet they ferment just fine.
Thanks. Your replies mostly confirm what we have experienced.
Wanted to check with the brewing experts here, as I did see some info regarding dropping the temp too quickly.
I am not an expert on yeast biology, but I would expect the reaction to a sudden temperature drop to depend on the state of the yeast at the start. If they are in the middle of an active fermentation I can imagine that a sudden temperature drop would cause metabolic havoc and could result in unwanted byproducts. On the other hand, if they have finished fermenting and are flocculating and preparing to go dormant already then the temperature drop would be inconsequential.
Again, that’s not what Palmer says. But it is what experience has shown me to be the case.
This is true of any fermentation, and I think it really has nothing to do with the yeast being “temp-shocked,” which I don’t think is a thing–at least, not a thing that matters in the slightest.
Yeast produce all kinds of nasty stuff even in the healthiest, most optimal, most perfect fermentations. Some of this leaks out of the cell. If you don’t give the yeast time to clean it up, then of course these byproducts–diacetyl, acetaldehyde, sulfur–can be readily tastable. But this isn’t due to metabolic havoc per se, it’s simply because the yeast weren’t given enough time to finish the job.
In this example, the beer had fermented at 48 degrees for two weeks. Then the temp was raised to 62 for 5 days, just to clean up any unwanted off flavors. A gravity reading was taken today, showing Brix at 9.6. The original Brix was 17.2.
That equates to 6.7% ABV, which is way over the target for a Festbier.
It is crashing right now, going down to 32 for about 5 or 6 days.
When I looked into the top of the beer, it is very cloudy, and does not look like the yeast was dropping much at all.
9.6 brix? That’s nearly 1.040 SG. Are you sure that is correct?
The online calculator with alcohol present showed 1.020. The Northern Brewer calculator showed 1.018.
I believe those numbers. Taking about a 1.5 ounce taste sample, I could feel the alcohol right away.
I should have checked my library before responding, but better late than never. Here is a quote from Yeast, by Chris White and Jamil Zainasheff, p. 114:
As far as yeast activity goes, crashing the temperature or lowering it slowly makes little flavor difference if you are dropping the beer below 40 F (4 C). However, a very rapid reduction in temperature (less than 6 hours) at the end of fermentation can cause the yeast to excrete more ester compounds instead of retaining them. In addition, if you plan to use the yeast for repitching, you should avoid rapid temperature changes (up or down), as they can cause the yeast to express heat shock proteins
No mention of lipids, only esters.
I better put the brakes on, and right now!
My fermentation freezer takes the better part of day to go from 65F to 34F with a lager after diacetyl rest. I have tasted no off-flavors.
Same here. But I slowed the temp drop a bit, sitting at 40 F now, will drop to 32 in the morning.
Never had any bad experience before with the rapid crash technique.
Old topic I know, but I thought I would share my experience which has shown me that Palmer is correct. I heard Bamforth speak on the topic and he blathered on and on about how they crash cooled Carling Black Label… blah blah blah… but in the end he agreed that shocking the yeast releases proteolytic enzymes reducing foam. YMMV, but I believe slow crashing has a benefit but also the cost of time.
I have not had a problem crashing. Until I do, I’ll keep doing it.
Lipids and proteolytic enzymes are two different things. It doesn’t sound as if Bamforth was in complete agreement with Palmer.
I cold crash as fast as I can in a fermentation fridge and haven’t had any problems.