Diacetyl Rest: Misnomer?

Isn't the term "diacetyl rest" a misnomer? I mean, the whole point is to give the yeast a metabolic boost to help it reduce the diacetyl in the beer.

Just thought I'd put that out there... raise it up the flagpole and see who salutes... see if that dog won't hunt, monsignor...

-Steve

I think by rest they mean vacation. Imagine all of the people up north that take their winter holiday in Jamacia.

Also, I think you have been synergizing a bit too much.

Yeah, I suppose the yeast are doing the opposite of resting during that period of time. Your observation may have some validity. I'm sure a beer geek will be along shortly to point out the reasoning behind the term.

Could be named that since it's a similar process to resting during the mash when doing a multi step mash. Dough in at 133, rest for 20 min, etc.

Bing! Give dstar26t a cigar.

"Rest" refers to a temperature plateau.

Ain't brewing jargon neat?

Bob

It is a misnomer because the only reason you should need a diacetyl rest is if you screwed up the fermentation somehow.

I prefer to call it an attenuation rest.

ChrisKennedy said:

It is a misnomer because the only reason you should need a diacetyl rest is if you screwed up the fermentation somehow.

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... or if you used a strain that produces a lot of diacetyl.

Aside from perhaps Ringwood, very noticeable diacetyl from any strain is a problem from fermentation handling.

ChrisKennedy said:

Aside from perhaps Ringwood, very noticeable diacetyl from any strain is a problem from fermentation handling.

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I respectfully disagree with this. Lager yeasts often produce diacetyl during normal and proper fermentation. Some more than others and some not at all. It's rather rare for an ale yeast to produce diacetyl IIRC, but not for lager yeast.

You got some strains in my mind? Because the ones I have used have never produced noticeable diacetyl with proper pitch rates and after pitching cold.

Wyeast 1007, for example, is a notorious diacetyl producer. A diacetyl rest is good insurance whether or not you detect any during fermentation. Actually, I haven't experienced any excessive diacetyl levels in my beer either. My comments are based on reading what the experts like Noonan have written. My understanding is that diacetyl can be produced in more than a few different ways both by yeast and some types of bacteria and sometimes its presence is irreversible with or without a rest. I think traditional kraeusening was developed at least partly to to mitigate diacetyl in lagers. I don't fully understand all the microbiology and chemistry that involves diacetyl production and reduction as it is quite complex and way over my head. I do the rest mostly as a precaution figuring it can't do any harm.

I do a ramping up of temperatures too.

My main point is that needing a diacetyl rest to actually reduce diacetyl should not be a part of your normal procedures because you should never need to reduce noticeable diacetyl in the vast majority of fermentations. If you are getting noticeable diacetyl, you should work to fix what is producing the excess diacetyl in the first place, and in my experience, the vast majority of yeast will not produce enough diacetyl to be noticeable at any point in the fermentation if they are treated correctly, 1007 included.

IIRC, all brewing yeasts produce diacetyl in some amounts. With most ale yeasts, the yeast activity is high enough that the diacetyl is consumed as a regular part of the fermentation process. With lager yeasts, the lower fermentation activity can, as a result of the lower fermentation temperatures, cause some diacetyl to be "left over". The rise in temperature occasioned by the rest causes the yeast to "speed up" and consume the excess diacetyl.

I guess, even though the yeast activity actually increases, you could call it a "rest" from the lager fermentation.

Mr Kennedy,

If that works for you, great! Most other brewers don't have that fortunate circumstance. For them - including me - a short diacetyl rest harms nothing, even if it's not strictly necessary.

Remember, there need not be perceptible diacetyl in the beer at the time one would normally conduct the rest for diacetyl to be found in the finished beer. Uptake of precursors is also a function of the diacetyl rest.

I don't know that I'm comfortable with such generalizations as "the vast majority" of anything. Lager brewers large and small the world over would disagree. There are more than a few yeasts which throw perceptible amounts of diacetyl, and even those which often don't are capable of it unless meticulous care - care a homebrewer can seldom take - is taken. In those cases, more common than I suspect you'd care to admit, the thing that'll fix excess diacetyl is ... a diacetyl rest during the ferment.

Cheers,

Bob

I am merely trying to say that if you are consistently getting noticeable diacetyl, you may have room for improvement in your fermentation practices and that overly relying on diacetyl rests to reduce their levels is treating the problem instead of fixing what is causing the problem.

And again, I do "diacetyl rests", just not to mainly reduce diacetyl levels. If I screwed up somewhere during fermentation and more diacetyl was produced than normal, then this will help that. But my main purpose is for attenuation.

NQ3X said:

Bing! Give dstar26t a cigar.

"Rest" refers to a temperature plateau.

Ain't brewing jargon neat?

Bob

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Fine... ruin my smug sense of self-satisfaction...

-Steve

SavageSteve said:

Fine... ruin my smug sense of self-satisfaction...

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I told you some beer geek would come along and rain on your parade.

I don't think it's anything more than a matter of linguistic efficiency. Why say "diacetyl reduction rest" when you can say "diacetyl rest" and have it mean the same thing. No one does a rest to increase diacetyl, and I don't know that you even could.


TL