Bock And Diacytel Rest

[MHD]

Morning all, brewed a bock last night (first Larger) pitched at 19 degrees and put it in the fridge to brew at 11 degrees...

When should I do a diacytel rest? and at what temperature given room temperature in the gaurage is ~14 degrees!

 

[Hubby]

There are some slightly different approaches to the diacetyl rest - a search will bring up a range of them (ie when to do it and the temp vary slightly).

As a general guide, consider when fermentation has slowed and SG is about 3/4 of the way to target FG. Temp range of the rest can be between 14 - 16 degrees C for 24 - 48 hrs and the duration may depend on how long it take to get the fermenter up to this temp. I'd suggest you also have a look at: J Palmer: Section 10.4 Yeast Starters and Diacetyl Rests (suggesting appr 13 - 16 degrees C for the rest).

In terms of getting the fermenter above ambient temp, have you thought about a low watt heater in the fridge - eg heat pad (NOT in contact with ferm) or low W light bulb with temp controller or on timer (watched carefully)? I used this method recently with good results.

 

[Trough Lolly]

One thing to note guys...if you give the bock a diacetyl rest before primary fermentation has completed, ie, at 3/4 of the way to target FG, you might be getting rid of the diacetyl, but the downside is the potential to inadvertantly add fusels to the beer since the yeast is still actively fermenting the beer and you're upping the fermentation temp at the same time.

This is why I prefer a minimum 48 hour rest at around 18C, when the beer has completed primary or as John Palmer himself has written;
[quote name='From John's book online...']This rest at the end of primary fermentation consists of raising the temperature of the beer to 55-60 F for 24 - 48 hours before cooling it down for the lagering period.[/quote]

Cheers,
TL

 

[Ross]

Diacetyl rest needs to be done before terminal gravity. The risk of fusel alcohols once the brew is below 1020, I believe is negligable & far outweighed by the need to remove diacetyl with some yeasts.

Below is a transcript from a talk with Chris White (whitelabs):

[dgonzalez] i think some of the guests might find this topic interesting. can you describe, in simple terms, how a diacetyl rest works? it's benefits? and downfalls of not doing one?
[cwhite] yeast make a compoud called acetolactate.
[ale] Excellent question, DG.
[cwhite] This goes outside the cell, where it is later oxidized to diacetyl.
[GSchmidt] ?
[cwhite] If yeast are still there and are metobolicly active, they will reabsorb it. If the yeast are removed, or are done, they might not reabsorb the diacetyl.
[cwhite] For lagers, you need to raise the temperature to ~65 for 1 week, starting when the beer is about 1.020. If you go much lower then that, the yeast will not be working strong enough to take up the diacetyl.
[cwhite] For ales, you only need to go 24-48 hours post terminal gravity, since you are already at ~65 F temperatures. This is why lagers will taste buttery later, you can't taste the precurser, and once you remove the yeast, it will turn into diactyl later.
[cwhite] end


Cheers Ross

 

[MHD]

So how's this for a ferm schedule:
*Primary for ~ 1 week
*raise primary to ~15 degrees for 48 hours
*Rack to a secondary fermenter (get it off the trub)
*Drop that secondary to 11 degrees for a few days (just to finish off any complex sugars
*Then drop to ~2 degrees for about a week (cold condition/larger)
*Transfer to bottling bucket + prime +bottle...

 

[Trough Lolly]

Diacetyl rest needs to be done before terminal gravity. The risk of fusel alcohols once the brew is below 1020, I believe is negligable & far outweighed by the need to remove diacetyl with some yeasts.

I see the point you make, Ross, and readily concede that the likelihood of adding fusel oils to the beer is low - which is why I mentioned the potential, not certainty of adding fusels, in my response - but I'd humbly submit that raising the temp of a lager in primary (admittedly late in primary) may cause more problems that it solves especially if brewers are new to cold fermentation practices.
With all due respect to Chris White, unless you have an extremely flocculant yeast strain, there should be plenty of yeast in solution after 2 weeks of fermentation, to scrub out the diacetyl - otherwise we'd never naturally carbonate bottle lagers without adding yeast during bottling which incidentally I never had to do before the kegs arrived - even after lagering for a month.
Apologies for questioning conventional wisdom, but I'm just going off my own experience... h34r:

Cheers,
TL

edit: spellunk...

 

[Hubby]

Apologies for questioning conventional wisdom, but I'm just going off my own experience... h34r:

That's what's so good about these forums and hearing what others have done ... esp what works and what doesn't. I haven't done enough lagers to compare and to test small differences in procedure. Has anyone had noticable differences?

So how's this for a ferm schedule:
*Primary for ~ 1 week
*raise primary to ~15 degrees for 48 hours
*Rack to a secondary fermenter (get it off the trub)
*Drop that secondary to 11 degrees for a few days (just to finish off any complex sugars
*Then drop to ~2 degrees for about a week (cold condition/larger)
*Transfer to bottling bucket + prime +bottle...

[post="122234"][/post]​

This seems like a very short lager period. What yeast did you use and have thought about a longer lagering period - esp for a bock? Also, make sure you bring the brew up to room temp before priming/bottling (ie to release CO2) - have a look at A Primer on Priming.

 

[Guest Lurker]

Diacetyl rest needs to be done before terminal gravity. The risk of fusel alcohols once the brew is below 1020, I believe is negligable & far outweighed by the need to remove diacetyl with some yeasts.

[post="122233"][/post]​

I agree it generally works better (quicker) before terminal gravity, I like to pull them out of the fridge below about 1.015. But if you read HBD and Craftbrewing, there are award winning lager brewers who claim never do a diacetyl rest, the yeast are active enough to clean it up at fermentation/lagering temperatures, it just takes a hell of a lot longer.

 

[Trough Lolly]

Good point, GL - the key to making good lagers, IMHO, is patience...

Cheers,
TL

 

[MHD]

hehe... being a bock and starting at 1065 I would be suprised if it got to 1015...

So longer in secondary then,,, How long? (in a hdpe ferm)

Also, when rasing the temperature of the secondary do the chill haze protiens get reabsorbed?

 

[Trough Lolly]

MHD,
Without knowing the recipe and mash procedure, I'd only be guessing as to how your final gravity will turn out - so I won't - you want facts not assertions or guesses, but as you suggest, it's unlikely that you'll have a low finishing gravity which is another reason why switching to lagering mode simply because the beer arrived at a certain gravity is risky to say the least...
Logic tells us that any temp shift will affect the beer - but as to whether that is a -ve change or even a lasting change, depends on the composition of the beer after primary fermentation. I'd suggest that it's unlikely that protein haze will be a major issue, since you'd expect a relatively short diacetyl rest, followed by a decent period of lagering to further refine the beer, followed by bottling thereafter. And I'd strongly recommend you racked the beer off the yeast cake before you do any lagering. Consider the lagering tank to also act as your beer brightening tank.
I'll happily consume your primary yeast slurry on cold, dry toast, if you don't find any sediment in the bottom of your secondary / lagering tank after 8 weeks lagering at 3C....!

Cheers,
TL
Edit: spelling! Damn this pils is good!! B)

 

[Ross]

\
With all due respect to Chris White, unless you have an extremely flocculant yeast strain, there should be plenty of yeast in solution after 2 weeks of fermentation, to scrub out the diacetyl - otherwise we'd never naturally carbonate bottle lagers without adding yeast during bottling which incidentally I never had to do before the kegs arrived - even after lagering for a month.
Apologies for questioning conventional wisdom, but I'm just going off my own experience... h34r:
\

[post="122276"][/post]​

My understanding was that the yeast still needs to be in an "active" phase, to clean up the diacetyl, rather than just in solution - but hey, I could easily be wrong...

cheers Ross

 

[Trough Lolly]

[snip]
My understanding was that the yeast still needs to be in an "active" phase, to clean up the diacetyl, rather than just in solution - but hey, I could easily be wrong...

cheers Ross

[post="122399"][/post]​

Not at all Ross, you're quite right!
//warning - serious beergeek mode on!//

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?! h34r:
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!! B)
Cheers,
TL

 

[smashed jaffa]

TL,

You blow my mind dude :super:

I have just finished a diaceytel rest on my first lager! (quasi Munich Helles partial)

And I thought that you had the rest at the end of primary, as you have just so eloquently stated. I must have read the right posts or something :lol:

Good read. I think I understood most of your post.

Cheers, you have confirmed my thoughts on this seemingly complicated subject.

Smashed Jaffa.

P.S Dem some big words for a vicar! LOL

 

[Ross]

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.
TL

[post="122601"][/post]​

I'm sure Whitelabs or wyeast would enlighten you further - why not drop them a mail & share your findings...

cheers Ross

 

[Trough Lolly]

Bloody hell! I reckon those blokes would blow my mind if I got in touch with them, but yeah I suppose it's worth asking - however, let me check on hbd.org to see if the topic's been discussed during their fortnight of yeast questions that they do each year with the yeast gurus...
I must admit though, its strange that many books and knowledgeable people write about alpha acetolactate precursors and diacetyl itself and there are plenty of scientific papers on how to reduce diacetyl levels and the precursors etc but I've had trouble finding decent articles on whether anyone is looking at genetically modifying yeast cells to reduce the precursor secretion levels, ie prevent rather than treat. As I mentioned before, different strains secrete the precursors at different rates - surely somebody can find out what it is that makes some strains secrete less precursors than others?
Perhaps it's because anyone who can genetically modify a single celled organism in this manner will not only corner the market, by drastically reducing maturation times at commercial breweries (so they'd do this research in secret), but they'd also potentially have to run the gauntlet of being accused of making GM beer!! :blink:

Sounds more like an X-files episode rather than brewing bloody beer!!
Anyway, I think the topic is done to death and once again I apologise for going over the top on this issue...'nuff said...

Cheers,
TL
Edit: sp.

 

[Ross]

and once again I apologise for going over the top on this issue...'nuff said...

[post="122652"][/post]​

Don't apologise, your posts are always informative & a great read - even if some content goes straight over my head ...

Cheers Ross...