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We have brewed a number of ales, but recently tried our hand at a pilsner.

After 8 days of fermenting at around 52 degrees F, we brought the pilsner up for a 2-day diacetyl rest at around 68 degrees. At this point we proved our inexperience by moving the carboy back into the cooler to crash without racking over. Unsurprisingly, we discovered off flavors, most notably strong diacetyl, when we were preparing to rack over into kegs to serve.

What would be the impact of bringing the carboys up for a second d-rest at this stage?

Will the yeast have enough left in them to dispose of the diacetyl? Are we inviting autolysis?

Any suggestions to salvage the beer?

We are trying to avoid repitching yeast, but if that's the only way, we're open.

Another technique we've read about is bubbling CO2 through the beer and purging the gas repeatedly. Has anyone tried this?

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2 Answers 2

up vote 3 down vote accepted

Traditional German brewers would use a krausen from an actively fermenting batch to carbonate and this would also reabsorb the diacetyl. You can do the same thing by priming and pitching a pack of yeast and the secondary fermentation should do the trick.

A diacetyl rest at this point will not effective since there is very little active yeast in the beer at this point.

I have not heard that bubbling CO2 through the beer will remove diacetyl.

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Alright; that's what we were afraid of. Any suggestions on yeast to pitch for this purpose? –  distractable Apr 25 '11 at 20:13
    
I usually use Nottingham dry yeast since it is neutral and highly flocculant and is relatively cheap. If you want to use a lager I would use the safelager 34/70 or the S-23 but run as much as the liquid. –  Northern Brewer Chris Apr 25 '11 at 20:51

Are you sure there isn't another issue here as to why you're getting off flavors? I've lagered in my primary for 3 weeks before without experiencing any diacetyl. If anything I would think letting your brew rest on the yeast cake would help clear out even more diacetyl.

From what I understand, autolysis takes at least a month to occur, even longer at lagering temperatures, so I doubt that would be an issue. Even if it was, I think the flavors it produces are totally different (rubbery band-aid as opposed to butterscotchy diacetyl).

As John Palmer stated:

I should mention that by brewing with healthy yeast in a well-prepared wort, many experienced brewers, myself included, have been able to leave a beer in the primary fermenter for several months without any evidence of autolysis.

As for activating your yeast again, you could rack your beer, then make a starter from the yeast cake to re-pitch it to your batch.

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