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Following the suggestion of my LBS, I made an Oktoberfest using a hybrid yeast (Wyeast 2565) because I didn't have a lagering fridge set up yet--bought myself at least 2 weeks before needing to crash cool, and got a setup to chill in time. The problem is, when I did I accidentally chilled it a bit much--enough to make a layer of ice on the top (don't trust the thermometer enough for a reading to really matter).

I know that will obviously change the flavor (don't know how), but my concern is that the wyeast will not activate again for bottling. Since I can't provide the lowest temperature it hit, I know no answer is definitive, but what are the chances enough survived to bottle, and reasonably how cold can wyeast get before it won't reactivate--or is that dependent on the strain?

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For future reference, 2565 is a kolsch yeast with a distinct flavor profile. Not a very good choice for a pseudOfest. –  Denny Conn Aug 13 '13 at 17:15
    
What would you recommend? The other suggestion I heard was just German Ale. –  nfrye Aug 13 '13 at 17:31
    
Yes, WY1007 is a great yeast for making pseudolagers. It works well down to 50 F (at which point you could use a lager yeast anyway!), but is very clean even in the low 60s if that's all you can manage. Even WY1056 would have been a better choice than 2565. –  Denny Conn Aug 13 '13 at 18:30
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1 Answer

up vote 2 down vote accepted

As long as it was just a layer of ice on the top, the yeast should still be fine, since the rest of the water was still at or above freezing.

Yeast can withstand very low temperatures - I freeze them in glycerine solution at -36°C/-32°F, while commercial yeast banks freeze yeast at much lower temperatures - ca. -60°C/-80deg;F. What kills them when freezing in mostly water is ice crystals that form, which penetrate and rupture the cell. But in your case, since the ice was just on top, most of the water didn't hit freezing and some of the yeast has still probably survived.

If you want to be totally certain you get carbonation when you prime, you could add 1/2 tsp dried yeast at bottling time (to the whole batch.)

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Thanks! Figured that was the case, but wanted to be sure. What kind of dry yeast would you suggest? –  nfrye Aug 13 '13 at 17:30
    
What other consequences come from a result of accidentally freezing beer? Are there any other ill-effects other than (potentially) harming/killing the yeast? –  Scott Aug 13 '13 at 17:48
    
There have been reports of permanent chill haze developing if you freeze the beer. Not a certain thing, but a possibility. –  Denny Conn Aug 13 '13 at 18:32
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