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I have my first lager fermenting at 50 degrees (pitched Saturday 8/18 at 11pm, tonight will be pitch + 5 days). Airlock activity started Monday AM, been going consistently since.

The problem I am seeing is, I am heading out of town one week from today for 10 days (which will be pitching + 12 days). I have two choices: raise it up to diacetyle rest temp prior to leaving, or leave it in the primary at 50 degrees until pitching + 22 days. I feel like the former will not facilitate an actual diacetyl rest as the yeast will have gone dormant.

I know ideally, it should be done for a few days when you have reached 75% or so of your target gravity (maybe 50-60% attenuation).

My question is, which side of error will produce a cleaner lager?

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2 Answers 2

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I would do it later rather than earlier. By raising the temperature early, you risk introducing esters, fusels and sulphur compounds into the beer, which can't be cleaned up easily. Traditionally the diacetyl rest is done after primary, not during it. (see reference below.) So you should be fine just leaving the beer.

When you get home from your trip, take a gravity sample and taste the beer - you may find you don't need a diacetyl rest at all. It's not always necessary. But if you feel it is, then I doubt all the yeast will have gone dormant after 3 weeks and you will probably be fine just raising the temperature for a few days. Again, take a sample afterwards for comparison.

If there is still diacetyl, you can krausen the beer by pitching a quart of fresh wort and actively fermenting yeast. (Either a lager strain or a neutral ale yeast.) This will clean up the beer very well. (Especially ale yeasts, which have a higher absorption capacity for diacetyl.)

See

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Give your lager a nice long fermentation (say 4 weeks) with plenty of healthy yeast and it's unlikely you'll need a diacetyl rest. I typically take a gravity reading after 4 weeks and taste the sample. If there is diacetyl, I do the rest at that point. If I don't taste it, it doesn't need the rest. BTW, I don't think the yeast will necessarily be dormant. Even if it is, the purpose of raising the temp for a d rest is to make the yeast more active so it will consume the diacetyl. That's why if you pitch enough yeast and give it enough time it's likely to consume the diacetyl during fermentation and you won't need a d rest.

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Plus of one pitches the yeast at or below fermentation temps (say 48F) and allows it to heat up to fermentation temp naturally, diacetyl is rarely a problem. –  brewchez Aug 23 '12 at 23:18
    
Interesting. So high temps at the end clean up diacytl, but low temps in the beginning prevent it? Almost sounds counter intuitive. –  Graham Aug 24 '12 at 14:21
    
It's not the high temps themselves clean up diacetyl. The higher temps make the yeast more active and the yeast cleans it up. –  Denny Conn Aug 24 '12 at 15:01
    
Right and the lower activity at cold temps prevents it from being formed in great quantities to begin with. –  brewchez Aug 24 '12 at 20:46
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