Diacetyl Rest

[Clean Brewer]

Hello all,

I brewed a lager late last month, it was at 12c for 2 weeks and then I racked it off and gave it 3 days at 18c. It is now lagering at 3-4c.

Question is, will it have an affect by racking it first then giving it its diacetyl rest before lagering?

Is it best to leave it in primary for its diacetyl rest then rack it?

Cheers

[warra48]

I think it's best done in primary, so the full complement of yeasties can do their thing and clean your brew.

[hoohaaman]

Clean brewer,you know the most important thing about craft brewing?

PATIENCE,AND waiting a bit longer.

[Clean Brewer]

I am understanding the PATIENCE thing now and taking it alot easier..

And after good advice from people I did what I had to do, the only question I had was: Does it have a negative impact by racking before giving it its diacetyl rest?

The beer was cleared up quite nicely and I could only imagine that racking it off first wouldnt have been so bad, as it would have resuspended and gave some of the yeast a stir up and could go to work for those 3 days before lagering....

True?

[warra48]

Yup, you can do it after racking, but why handicap yourself ?

It's like running the City to Surf with one lung shut down. You'd finish, eventually, but why do it the hard way?

[Clean Brewer]

I understand, it was actually a mistake when I did it.

I just needed to know that it would be ok...

[rwh]

It'll be just fine. It's actually the yeast in suspension that do the lion's share of the work. Diacetyl's an "easy" food for yeast anyway.

[Biernut]

This following extract regarding "Diacetyl Rest" from wikipedia probably explains it best.

Diacetyl at high levels produce a buttery or butterscotch flavour to your brew. It is produced during fermentation as a by product of valine synthesis.

Diacetyl rest entails elevating temperatures slightly for two or three days after fermentation to allow yeast to absorb the diacetyl it produces earlier in the fermentation cycle

The article goes into depth regarding this topic for those technically inclined.


Cheers.

[Trough Lolly]

A few of us had a chat on AHB about diacetyl back in 2006. Here's what I wrote:

There are, however two problems that make the elimination of diacetyl quite challenging. The first problem is the presence of the precursor to diacetyl and the second problem is the characteristics of the yeast strain itself.
The generation of diacetyl in beer is not actually dependent on the yeast. The diacetyl precursor - alpha acetolactate - undergoes a spontaneous oxidative decarboxylation and converts into diacetyl (2,3-butanedione). Two major influences in this process are pH and temperature (there are, of course, other factors including oxygen levels and oxidative ions such as iron or copper that also convert the precursor to diacetyl).
Taking a step backwards, we need to understand how the alpha acetolactate got there in the first place and the prime culprit is the yeast itself - generating the alpha acetolactate as a result of synthesising valine and leucine amino acids from the wort during the "active" or attenuative phase. The fact is that if we could use a yeast strain that didn't generate any alpha acetolactate, or we got hard core and added alpha acetolactate decarboxylase that converts the alpha acetolactate to acetoin and bypasses the diacetyl stage, we wouldn't have any diacetyl. The yeast strains that we use do unfortunately secrete alpha acetolactate, but that rate of secretion does vary between strains.

So, the problem we have is active yeast that yes, is quite capable of scrubbing out the diacetyl present in the fermenting wort, but at the same time, is quite possibly still secreting the diacetyl precursor. And this is why I'm not all that convinced that giving the beer a diacetyl rest when the attenuative phase is not complete, is the best solution. Yes, it works, but it's possible that the diacetyl rest is better done in the window of opportunity between the end of primary fermentation and when the yeast is flocced out and dormant, ie there is still yeast in suspension, before lagering, that still have diacetyl reductases present to scrub the diacetyl out of the fermented wort...

This is demonstrated by brewers who experience "late bloom" diacetyl in their beer. They can't detect any diacetyl when fermentation has completed and they do a short diacetyl rest then rack to lagering or simply skip the rest and rack the diacetyl free beer straight to lagering, only to find to their dismay the presence of diacetyl some weeks later when they sample from the lagering vessel....Why is this so?!
A common answer is oxygen - unless you rack under CO2, you can inadvertantly add oxygen during racking into the lagering vessel and that oxygen converts the alpha acetolactate present in the pre-lagered beer, into diacetyl. And of course, since you lagered the beer, the yeast is inactive so it won't clean the diacetyl up...

Let me apologise for rabbiting on, but I'm not convinced that a diacetyl rest should be rushed into - I see your logic but it gets easily contradicted by the active yeast taking on the role of prime culprit in the precursor generation stakes. Perhaps the generation of the alpha acetolactate drops off substantially as we near the end of the attenuative phase - I don't have clear data on that, but I'm gonna stick to my standard procedure and do the diacetyl rest at the end of the primary fermentation and not beforehand.
//beergeek mode ends//

Whatever - hey, let's have a beer!!

To answer your question, it shouldn't matter whether you racked off the primary yeast cake or not. As RWH pointed out, the yeast in suspension will be enough to scrub out the diacetyl - but my personal preference is to perform the diacetyl rest at the latter part of the primary ferment, in the primary fermenter and not any sooner...

Cheers,
TL