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So an often repeated mantra for starters is to (1) make a starter, (2) let it ferment out completely, (3) chill the starter in the fridge for a day or two, then (4) pour/decant off the oxidized "beer" in the starter flask and then (5) pitch just the slurry at the bottom of the flask into the fresh wort to be fermented.

However, I was under the impression that yeasts did not like extremely rapid temperature changes, and going from 40F in a fridge to 65-70F in wort almost instantly seems pretty rapid to me.

I'm not particularly questioning the effectiveness of the technique, mainly because I hear so many brewers espousing it, but I am curious how many here do this for most starters, and if there are any strains where you need to do something different, like pitch the whole starter at high-krausen. I prefer that method, not based on anything real, but just because it makes me the least nervous. (I KNOW the actively bubbling starter is working.)

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I think you're right. I believe the unwritten step is to allow the starter to reach room temperature before pitching. At least, that is what I have done in the past and have yet to see arguments against it. –  Bad Neighbor Nov 3 '11 at 15:18
    
Don't completely decant either. You need a little of that liquid to help swirl up the yeast. Or replace it with sterile water prior to swirling. –  brewchez Nov 5 '11 at 11:50
    
Cool. And no one knows of any strains that need to be handled differently? Excluding the bizarre world of souring cultures, I'm just curious if any Sach. strains require different handling in the starter. –  Graham Nov 7 '11 at 3:59

2 Answers 2

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Temperature change is worst when the yeast is active, because it needs to change its metabolism to deal with the new temperature. This involves producing new enzymes, etc. which can lead to off flavors. If the change is too much, the yeast might just quit fermenting all together.

When you let the yeast ferment the starter completely and then chill them, they go into a dormant state and aren't really eating anything. They stay in this state while they warm up again and they don't really start metabolizing until they are back at a stable temperature in the wort. That being said, you should let the yeast warm to room temperature before you pitch it so fermentation doesn't start before it has warmed completely, then you might have problems with temperature shock.

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Chill, Decant, when you start brewing, pull the starter out and let it hang out and watch while you prepare it's new home/all you can eat buffet. This works great for me. A side benefit is it helps to wake the yeast back up after the chilling step.

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