How to tell if your lager needs a diacetyl rest

[menschmaschine]

Is it possible to do a diacetyl rest after fermentation completes? I have a lager that finished fermenting while I was out of town. Now it's cold and carbed, and has a pretty strong diacetyl taste. If I moved the kegs to a warm spot (around 70 degrees), is there any chance of the diacetyl going away or is this batch a lost cause?

Diacetyl can be cleaned up with a good lagering period. I'd lager it for the appropriate time, then taste it again. If the diacetyl is still there, let it lager longer.

 

[drunkatuw]

Diacetyl can be cleaned up with a good lagering period. I'd lager it for the appropriate time, then taste it again. If the diacetyl is still there, let it lager longer.

I brewed this batch on 1/1/09 and it's been lagering since early feb. I think the diacetyl is here to stay. I'm going to try making a starter and dumping it into the beer after it warms up.

 

[Revvy]

I've been adding T-58. It's not real fast flocculating. I can see is clear back up slowly in the bottles. I would be surprised if it wasn't eating up some diacetyl on the way down. Fermenting in buckets that's something I don't get to see happing in the primary.

I was thinking about this over the weekend when I read that you were using the t-58....seems like it would be eating up anything nasty as it was clearing.

(oh what is the "cake" at the bottom of the bottles like, btw, is it tight and compacted? Does it put really clear.)

Mensh, you said

The limited yeast activity during bottle conditioning is not enough to clean up diacetyl, if present.

do you have any documentation backing this up...It seems to me that the % of yeast is the same whether it is in a carboy during a d'rest , as it might be in the mini fermenter that is a bottle....If the ratio of diactyl is the same in the bottle as it is in the fermenter, and the yeast is the same, why would the trace amount of yeast left clean up the trace amount of diacytl not be enough? This is pretty much a form of condtioning, not much difference if it's happening in the bottle or in the fermenter....

Maybe.

 

[SpanishCastleAle]

Revvy (all),
I have read that once the yeast are done consuming the sugars (or close to it)...that they then turn to consuming other things and these 'other things' are the 'cleaning up' we often refer to. So I just assumed that diacetyl was one of these 'other things' that the yeast consume only when they are running out of sugars. But the timing of the diacetyl rest doesn't really support that...unless the timing is purely to ensure that there is sufficient yeast still in suspension.

Do you know if diacetyl is one of these 'other things' the yeast consume only when they are running out of sugars? Mensch? Does the presence of alcohol play a role?

 

[menschmaschine]

Mensch, you said

do you have any documentation backing this up...It seems to me that the % of yeast is the same whether it is in a carboy during a d'rest , as it might be in the mini fermenter that is a bottle....If the ratio of diactyl is the same in the bottle as it is in the fermenter, and the yeast is the same, why would the trace amount of yeast left clean up the trace amount of diacytl not be enough? This is pretty much a form of condtioning, not much difference if it's happening in the bottle or in the fermenter....

Maybe.

As for documentation, I'd have to research it and it might not be a cut-and-dry statement. One thing I can say is that I've never read that a significant amount of diacetyl can be reduced in the bottle. All the texts I've read indicate a diacetyl rest to be done as fermentation is coming to a close, but before fermentation is finished.

As you know, when the yeast begin to run out of sugars to metabolize, they begin metabolizing other compounds, including ones they've already produced (like diacetyl). At this point, fermentation is still going and there are a lot of yeast in suspension. If the level of diacetyl is above taste threshold, the yeast activity is enough to take it below taste threshold.

In bottling, yeast have gone "dormant" and fermentation activity is restarted with the introduction of new sugars. When this "refermentation" dies down, I don't believe there is enough yeast activity to significantly clean up diacetyl. So, the difference is that there are a lot more yeast in the beer and in suspension as primary fermentation is coming to a close than there are in the bottle. Perhaps a small amount of diacetyl could be cleaned up, but I wouldn't rely on that method as a diacetyl rest.

 

[Malticulous]

You can bottle as so as it is at FG (read Kaiser's Wiki.) This would be before the yeast are completely dormant. The draw back is larger amounts of sediment.

Ravvy, T-58 is great. I get no pepper from the 1-3 point drop in the bottle and it sticks to the bottom after a few weeks.

 

[AnonyBrew]

Diacetyl can be cleaned up with a good lagering period. I'd lager it for the appropriate time, then taste it again. If the diacetyl is still there, let it lager longer.

This goes against what Boerderij_Kabouter said.

A d-rest should be done when about 3/4 of the fermentable sugars are eaten. If you wait to long, the yeast will have no food to fuel the rest and it will be a waste.

So who's right?

 

[Boerderij_Kabouter]

page 185 of Noonan describes the two typical ways to get rid of Diacetyl:

1: Discussing late Kraeusen

Generally, four to six days after high kraeusen begins (six to ten days after pitching), the formation of the foam cover ceases. As the availability of fermentable extract drops during the post-kraeusen stage, the yeast adapt to changing conditions by accelerating their secretion of extracellular enzymes capable of splitting off glucose from dextrins in solution. Reasonable levels of diacetyl and the related diketone 2,3-pentane dione are also absorbed and metabolized by the yeast. It is important that the fermentation temperature not be prematurely lowered and that the beer not be racked off its yeast sediment until the diacetyl has been reabsorbed. With a clean fermentation, it is usual for the beer to be held in the primary fermenter for two or three days after the krausen head has fallen, with the temperature being lowered from 45 degrees F (7 degrees C) to 38 to 40 degrees F (3 to 4 degrees C). The extract drop over the final twenty-four-hour period of primary fermentation should be about .5 ºPlato (SG 1.002), and the density should be about one-third what the wort density (OG) was.

2. Alternative:

An entirely different approach is relatively common in modern ferementation cycles. When the density drops to about 1.5 ºPlato (SG 1.006) above the target terminal gravity, the brewer raises the temperature of the post-kraeusen beer to 52 degrees F (11 degrees C) or higher, and holds that temperature for two to seven days for a diacetyl rest to reinvigorate the yeast culture so that it will metabolize diacetyl, removing it from solution.

Because fermentable extract is rapidly consumed at the higher temperatures of the diacetyl rest, subsequent conditioning can be foreshortened. Secondary fermentation will be both subdued and brief, and lagering may require only fourteen to twenty-one days to achieve the same clarity and flavor stability (but not the same flavor development) that would be expected with the usual five-to-seven week secondary fermentation and lagering.

 

[Boerderij_Kabouter]

Page 169 and 170 talk about pitching cold to avoid large levels of diacetyl production. He suggests using a settling tank cooled to 39 to 43 degrees F and pitching there, then racking the beer to the primary fermenter within 12 hours.

 

[Boerderij_Kabouter]

On page 187, Noonan describes racking after primary fermentation before lagering:

Racking must be done without rousing or splashing to prevent oxygen from entering the solution. Oxygen in the beer past early kraeusen poses serious consequences to the beer flavor: oxidation of acetohydroxy acids int he secondary fermenter produces diacetyl that the yeast may not reabsorb...

 

[Boerderij_Kabouter]

The page 187 reference is what lead me to believe noticeable amounts of diacetyl left in the beer post primary fermentation will not be metabolized during the lager period.

Noonan does reference addition of krausen beer as a great way to reduce diacetyl.

 

[menschmaschine]

This goes against what Boerderij_Kabouter said.



So who's right?

Both. The best and most reliable way to clean up excess diacetyl is with a diacetyl rest. Lagering should not be relied upon as a diacetyl rest, but some diacetyl can get metabolized during lagering.

 

[menschmaschine]

The page 187 reference is what lead me to believe noticeable amounts of diacetyl left in the beer post primary fermentation will not be metabolized during the lager period.

I don't disagree with that. I think we tend to look at this type of stuff with expectations of black and white, i.e., diacetyl or no diacetyl. I think it's more about how much. IOW, if there is a slightly noticeable level of undesired diacetyl at the end of primary and no diacetyl rest was done, I would wait to see how it tasted after lagering before taking action because some of these compounds can slowly get metabolized during lagering... after all, that's part of what lagering is for.

But if there was a very noticeable taste of diacetyl at the end of primary with no diacetyl rest done, action such as krausening would be a great idea. I think we're all on the same page here, we're just hammering out the details.