# Diacetyl rest



## jkhlt1210 (29/8/14)

G'day guys just wondering about doing a diacetyl rest. Is it worth doing to every brew or is there particular ones like lagers? Any advice appreciated


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## philmud (29/8/14)

Someone else may be able to expand on this, but a D rest is par for course with lagers (more likely to develop diacetyl), but often not required for ales. I asked this question a couple of years ago re: an ale & was asked if I could detect diacetyl in the fermented beer. I couldn't, and there was my answer.
Lots of brewers do let the temperature of their brew come up a few degrees at or near FG to make it easier for the yeast to finish any remaining sugar & clean up after themselves. I initially did confuse this process for a D rest.
A rule of thumb for lots of brewers seems to be a minimum of 2 weeks in the fermenter to allow the yeast to clean up & drop out. I usually go with this timeframe, although it also includes 3-4 days of cold crashing.


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## DJ_L3ThAL (29/8/14)

It depends on a few factors, I'd suggest learning what diacetyl tastes like and then taste for it in your beers. Took me a while to grasp the flavour but now I know it I can pick it.

If you cant taste it then there is no point doing a d rest unless you're entering comps.

I believe there is a slight difference between a proper diacetyl rest and simply raising the temp towards the end of primary ferment to encourage cleanup and promoting a higher attentuation also.


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## DJ_L3ThAL (29/8/14)

PI beat me to it


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## DJ_L3ThAL (29/8/14)

Yep to tack on to the end of PIs comment. Ive seen more and more brewers here doing 10 days at regular ferment temp, raise for 2-3 days then cold crash for 2-3 and dry hop during the cold crash. Ive employed this and reckon its a great schedule to brew to.


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## sponge (29/8/14)

I'll normally ferment at standard temps (beer/yeast dependent), then raise by ~3'C after ~5 days, leave for ~3days and CC for 3-7 days (with dry hopping if need be). I normally look at a 2 week turnaround, including CC. Haven't had any issues with the D at this stage (mind out of the gutter :lol: )..

Yeast health, pitching rates and oxygen will also play a vital roll as well.



EDIT: That was for an ale, obviously longer turnaround for a lager with a larger rise in temp.


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## philmud (29/8/14)

DJ_L3ThAL said:


> I believe there is a slight difference between a proper diacetyl rest and simply raising the temp towards the end of primary ferment to encourage cleanup and promoting a higher attentuation also.


Not having done a lager or a d-rest I could be talking out my arse, but I think a D-rest requires a gradual temperature increase to avoid shocking the yeast, whereas this isn't as crucial for an ale. Or perhaps it's not as crucial because the increase is less dramatic (eg 12C - 21C for a lager Vs. 18C - 21C for an ale).


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## Eagleburger (29/8/14)

I have noticed itseems to be yeast dependant. The bohemiam yeast I have needs 8-12 days at 20degc whilst the munich Ihave only needs 3-4. II would suggest going by smell and taste. My first butter bomb didnt occurr till after it was chilled in the keg. 

Methods I have tried to expadite the process includes, stirring the yeast, adding dex, keeping warm at 22degc, adding rinsed yeast, adding 10% from another fermenting batch that was at 50% attenuation. In spite of all these they all turned out great except for one that was a little dry and bland on account of the 500g of dex I added to assist with diacetyl clean up. It was still better than any thing I bought at the bottlo in a box.


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## philmud (29/8/14)

Eagle, does the dex work by rousing the yeast?


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## Eagleburger (29/8/14)

I believe so. 

I will be using bottle O2 on my next batch. Although I don't know if it will make a difference. All the batch s I havedone got to 75% attenuation in 3days and full attenuation in four days at 9 or 10 degC. . So its not like the yeast are stressed or lacking some thing. 

I read a post on hbt by a champion brewer, if you believe his sig, that it is OK to leave as long as it takes at 20degc or so. Two days sounds awesome atm. I am still in the stage where I Cant make it as fast as I drink it.


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## RobW (29/8/14)

There's a good discussion of lager fermentation and D-rests here:

http://braukaiser.com/wiki/index.php?title=Fermenting_Lagers


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## Alex.Tas (29/8/14)

From my limited understanding these are three main drivers for diacetyl production/control

grist: malt bill will play a large part. Pilsner malt will lead to a higher quantity of the precursor to diacetyl i believe. 

Yeast selection: some give more than others

Ferment temp: My understanding is that a D rest isn't usually required for ales because they usually ferment around 17-18 or so, and the yeast is able to remove the diacetyl at that temperature once its finished eating up the sugarz. Lagers usually require this temp increase step because they ferment around the 10-12 degree mark, and the yeast will more readily remove the diacetyl at the classic ale fermenting temperatures.

happy to be corrected however

Edit: have been corrected


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## DJ_L3ThAL (29/8/14)

I thought pilsner malt had more DMS precursors, not more likely to result in diacetyl which is a yeast and temp related byproduct?


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## verysupple (29/8/14)

Alex.Tas said:


> grist: malt bill will play a large part. Pilsner malt will lead to a higher quantity of the precursor to diacetyl i believe.


I've never heard that one before. Are you sure you're not confusing diacetyl with DMS? The precursor to diacetyl is alpha-acetolactate which is produced by the yeast in the process of making valine. The precursor to DMS is s-methyl methionine (SMM) which comes from malt.


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## Alex.Tas (29/8/14)

yeah perhaps you guys are right. my bad.
Regardless, how did i go with the other two points?


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## jkhlt1210 (30/8/14)

Cheers everyone for your replies


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## Eagleburger (30/8/14)

I just reread the article for the eleventh time. I am also going to try pitching less yeast.


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## manticle (30/8/14)

Posted a million times before but it's hard to get a better understanding of what and why from a source different to Dr Bamforth. Youtube search 'bamforth diacetyl' and have a listen.


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## citizensnips (10/7/15)

Without starting a new topic, I haven't brewed a lager in a long time and need to refresh my memory on D-rests. Can someone clarify for most of us brewers who like to leave our beer on the cake for 2 weeks to do its thing, what do you do in the case of a d-rest? If your raising temps at around 75-80% of your FG this is evidently going to be 5 days in or so. Do you then drop back down to regular temps for a week to let it sit for a total of two or just go straight to cold crashing or in this case lagering?


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## manticle (10/7/15)

Different approaches. I prefer to very slowly raise the temp when I'm part way through fermentation (1-2 degrees per day) then rest at ale temps for a few days, then slowly drop downwards toward lagering temps (0-4).

You can also do a forced diacetyl test to see how much precursor remains in the beer as that is the potential for diacetyl/vdk.


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## citizensnips (10/7/15)

That sounds like the go, lowering reasonably slow will give me enough time to let it sit comfortably at ferment temps.
Cheers manticle


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## bjbear77 (10/7/15)

citizensnips said:


> If your raising temps at around 75-80% of your FG this is evidently going to be 5 days in or so.


I have never had this happen with a lager, usually takes much longer


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## verysupple (13/7/15)

bjbear said:


> I have never had this happen with a lager, usually takes much longer


Sounds about right to me for an OG of ~1.050 at ~10 C. You have to pitch enough yeast, of course.


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## micblair (13/7/15)

You should do it for every beer -- as VDK-P isn't detectable until its converted to VDK. All I do is take a sample at the end of fermentation, microwave until I reach 60-70C (whilst cling wrapped), allow to cool, then smell/taste.


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## danestead (13/7/15)

bjbear said:


> I have never had this happen with a lager, usually takes much longer


I'm with you. I always do a starter yet my lagers ferment away at a maximum of 3 points per day. Are some people pitching much more yeast?


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## Tropico (13/7/15)

With this cold snap, it seems to be the season for lager.

Started one last Wed, pitched yeast at 15C, maybe a little warm but I thought it would drop overnight.

Came down to 13c by the next morning, and remained there till day 4, when it came down to 12c which was the setting for temp control (heat only).

Today, day 5, after it has looked more like an ale ferment than a lager, it actually looks like it has begun clearing (caught me by surprise actually).

The question is, if I slowly ramp up the temp, how high would be recommended max?


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## manticle (13/7/15)

Just ale temps is enough. 18-20.


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## Tropico (13/7/15)

Thanks, I'll go for 18 over 4 days


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## Rocker1986 (13/7/15)

citizensnips said:


> Without starting a new topic, I haven't brewed a lager in a long time and need to refresh my memory on D-rests. Can someone clarify for most of us brewers who like to leave our beer on the cake for 2 weeks to do its thing, what do you do in the case of a d-rest? If your raising temps at around 75-80% of your FG this is evidently going to be 5 days in or so. Do you then drop back down to regular temps for a week to let it sit for a total of two or just go straight to cold crashing or in this case lagering?


That's basically what I do yeah. I take the last two digits of the OG, halve it, and begin the temp rise when it gets down to that. My latest one's OG was 1046, but with a lower ferment temp of 10C I raised the temp controller when it was about 1026-27ish (day 5 in), to 19C, and just let it come up by itself inside the fridge. It took about 3 days to come up. I left it sit at the ale temps until a few days post reaching FG (1010 in this case), then I just went straight to cold crashing for two weeks before bottling, which will be on Sunday.

I kept the 1023 sample tube on the kitchen bench with the hydrometer in it so I could get a rough idea when it would probably be at FG, as it was basically sitting at the same temperature as the brew itself. It was at 1010 in about 9-10 days post pitching, so it got around 4-5 days post FG up there before being crashed. The FG samples tasted excellent too. Couldn't detect any buttery/butterscotch flavours that are associated with diacetyl.


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## verysupple (13/7/15)

danestead said:


> I'm with you. I always do a starter yet my lagers ferment away at a maximum of 3 points per day. Are some people pitching much more yeast?


Getting a little off topic, but others are probably pitching more yeast than you. I'm yet to do a lager since getting a stir plate but when I was using 3 L juice bottles and shaking it ever time I went past I would make a 1.5 L starter and then split that into 2 x 2 L starters. According to yeastcalc.com (using JZ/Mr.Malty growth model) that was giving me 480 - 520 b cells. I try to pitch 20 - 21 million cells / mL which for my typical OG of ~1.048 is about 1.7 - 1.8 million cells / mL / P.

EDIT: I should add that I try to pitch at about 8 C and ferment at 9 - 10 C.


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## danestead (14/7/15)

verysupple said:


> Getting a little off topic, but others are probably pitching more yeast than you. I'm yet to do a lager since getting a stir plate but when I was using 3 L juice bottles and shaking it ever time I went past I would make a 1.5 L starter and then split that into 2 x 2 L starters. According to yeastcalc.com (using JZ/Mr.Malty growth model) that was giving me 480 - 520 b cells. I try to pitch 20 - 21 million cells / mL which for my typical OG of ~1.048 is about 1.7 - 1.8 million cells / mL / P.
> 
> EDIT: I should add that I try to pitch at about 8 C and ferment at 9 - 10 C.


Interesting. I always pitch a 'calculated' 500b cells for 22L of roughly 1.050 wort, aerated with pure oxy. 500b cells is about a 25% overpitch so either some people are pitching much much more than me or there is something else different from the norm I'm doing.

I'd love my lagers to ferment quicker because it'd mean I'd be more inclined to brew them


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## seamad (14/7/15)

Is it yeast dependent ?
I've only made a few lagers with 2124 and with a pitch rate of 1.75 mil/ml/degree plato and pure O2 I get to @ 80% attenuation around the 5 day mark at 10C. It's been a while since I used s189 but at 13C i thought it was a bit slower.


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## verysupple (14/7/15)

danestead said:


> Interesting. I always pitch a 'calculated' 500b cells for 22L of roughly 1.050 wort, aerated with pure oxy. 500b cells is about a 25% overpitch so either some people are pitching much much more than me or there is something else different from the norm I'm doing.
> 
> I'd love my lagers to ferment quicker because it'd mean I'd be more inclined to brew them


Hmm, it's probably something else then. As seamad said, maybe the strain you use is just known to be a slow worker? I've used Wy2124, W34/70 and Wy2308. Always hit FG in about 5 days, never anything like 10 - 12 days.


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## Rocker1986 (14/7/15)

I can't say I've hit FG in 5 days with a lager yeast, but lately they've been there by day 9 or 10. Been using Wy2001 Urquell on the last few batches. I'd read a number of reviews of it taking 4 weeks to hit FG :blink: but haven't had that issue at all. I use the Brulosophy quick lager method, which only adds an extra week to my turnaround time compared to ales anyway.


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