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Old 12-11-2012, 09:26 AM   #1
pixelhussar
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Default when is yeast shocked?

I've read somewhere, that yeast should be pitched at fermenting temperature. In practice pitching yeast at room temperature and bringing the fermenter down to the (colder) cellar is very much a no no. Or temperature changes should be done gradually.

On the other hand I often read that finished starters can be put into the fridge to let the yeast settle at the bottom of the container.

What's the difference?

Thanks.

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Old 12-11-2012, 11:29 AM   #2
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When you put it into the fridge for a few days, the yeast will settle on the bottom and you can decant all the liquid above it, so that you can avoid potentially affecting the taste of your beer with so much bad-tasting starter "beer". Then you can pitch the yeast immediately, or allow it to warm up. Please note that if you're going to do this, you should allow the yeast to FULLY finish fermentation.

Personally, when I crash cool and decant my starters, I pitch them straight out of the fridge. This should actually be better than pitching at fermentation temps, because the yeast will still gave its glycogen reserves (rather than pointlessly using them while warming up).

You can allow it to warm up to fermentation temp first, but it's unnecessary at best, and somewhat detrimental at worst (I anticipate someone less familiar with the actual science will disagree with me here, but try it and I guarantee you won't regret it). That being said, it's still a lot better than pitching warmer than the desired fermentation temp as it can not only cause some degree of off-flavors (due to the higher than desired temps), but it can in some cases even cause fermentation to "stall" (due to the relative drop in temperature). So I'd ultimately recommend pitching the starter cooler than the wort it's going into (ideally straight out of the fridge), which should itself be (slightly) cooler than the temperature you'll be fermenting at.

The only other way I would ever suggest pitching a starter is when its krausen is peaking. This is usually best done to take advantage of the "inertia" of yeast cells which are already highly active, in circumstances where yeast that is pitched dormant might struggle. Since you need them to be active, you obviously can't decant, because you can't crash cool. This means that you need to consider how the significant volume of the whole starter might affect the flavor of your beer - whether the starter might be too large, the beer might be too light (thus allowing off-flavors to be more easily detected), etc. Volumes can be kept minimized (for any given cell count desired) by using a stir plate and stepping up multiple starters. For that reason (not to mention that it requires better timing), I don't use this method much anymore, and really only recommend it to try and restart fermentations that may have stalled, or for really high gravity beers, where the yeast can not only use all the help it can get, but also where a given volume of starter happens to have a far less noticeable on flavor anyways.

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Old 12-11-2012, 04:04 PM   #3
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Good reply! Here's a question: in an ideal world, should we be gradually cooling our yeast starters to fridge temp? I don't have time for this, but I've been wondering.

And to comment on the other side of the OP: the reason you don't want to start a wort at a higher temp and then lower to fermentation temp is because the higher temps will encourage quicker and unregulated growth of the yeast, which results in more precursors to off-flavors. If you pitch lower and then raise to an ideal fermentation temp, you're keeping the yeast by-products at a lower starting level, and the yeast will have less to clean up after fermentation is done.

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Old 12-11-2012, 04:05 PM   #4
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edit: double posted for some reason

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Old 12-11-2012, 04:19 PM   #5
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Quote:
Originally Posted by kanzimonson
Good reply! Here's a question: in an ideal world, should we be gradually cooling our yeast starters to fridge temp? I don't have time for this, but I've been wondering.
In an ideal world, yes. But to be honest I don't think it's going to produce a difference that's ever going to be noticeable to the drinker.

Where gradual cooling DOES make a significant difference though is when you're freezing yeast (usually for longer-term storage). But that's a whole 'nother animal entirely, so I'll just leave it at that.
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Old 12-11-2012, 05:33 PM   #6
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Alrighty, then to extend that idea, instead of crash cooling a fermentor post fermentation should we be slowly lowering the temp if we plan on reusing the yeast? Again, I usually don't feel like I have the time or patience for this. My thought is that I'd rather crash cool it, and then make a slightly bigger starter than any yeast calc tells me to make up for it.

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Old 12-11-2012, 05:40 PM   #7
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Quote:
Originally Posted by kanzimonson View Post
Alrighty, then to extend that idea, instead of crash cooling a fermentor post fermentation should we be slowly lowering the temp if we plan on reusing the yeast? Again, I usually don't feel like I have the time or patience for this. My thought is that I'd rather crash cool it, and then make a slightly bigger starter than any yeast calc tells me to make up for it.
"Crash" cooling means to cool quickly. That's the whole point, and it makes the suspended solids (yeast and other things like proteins) fall out due to the quick temperature change. Doing it slowly would mean not crash cooling, and would be something different entirely.

The yeast will fall to the bottom of the fermenter more quickly when crashed cooled, and that's why people do that.
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Old 12-11-2012, 06:01 PM   #8
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The only truly good thing about winter is the ability to crash and crash 'em hard. Sometimes crashing cider at 30* below zero can result in a far lower than expected yield if forgotten over night. Be sure to keep the resulting rhumatiz medicine from fire or flame. It can be used in airlocks. Hide it from your friends for their own protection.

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Old 12-11-2012, 06:45 PM   #9
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Quote:
Originally Posted by Yooper View Post
"Crash" cooling means to cool quickly. That's the whole point, and it makes the suspended solids (yeast and other things like proteins) fall out due to the quick temperature change. Doing it slowly would mean not crash cooling, and would be something different entirely.

The yeast will fall to the bottom of the fermenter more quickly when crashed cooled, and that's why people do that.
I don't believe that it's the quickness of the temp change that causes stuff to fall out. Cold temp below a certain limit will always make yeast go dormant, and therefore more likely to flocculate and then settle. As for proteins and junk, the colder it is the more they precipitate. The more solids present, the more likely they are to lump together, and larger particles settle more quickly than smaller.

But what I meant by my earlier question is should we be slowly lowering the temp of our fermentors if we want to optimize yeast health if we plan on harvesting and reusing? Again, I don't have time (when I'm thirsty for beer) to be lowering my fermentors by 1 degree per day. And big breweries generally do something more akin to "crashing" than a slow decrease, and I'm up for anything that mimics commercial brewing.
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Old 12-11-2012, 10:41 PM   #10
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I don't believe that it's the quickness of the temp change that causes stuff to fall out.
Well, you might not believe it- but it's true. That's why winemakers do it, and rely on it, while a slower chilling is great for things like lagers when you still have some work for the yeast to do. "Crash" cooling is a part of why the proteins precipitate out, and why the yeast fall out so fast, so that they can't acclimate to the cooler temperatures.

Cold crashing is fine for harvesting yeast- after all, you only want dormant (non active) yeast to be harvesting anyway. Crash cooling them makes them dormant.
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