How to tell if your lager needs a diacetyl rest

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nostalgia

nostalgia

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1. Take a sample of your lager after a week's fermentation.
2. Let a non-homebrewer buddy have a taste.
3. See how the conversation goes:

Buddy: "Mmm, tasty. What's that flavor? Tastes like...popcorn."
Me: "Butter?"
Buddy: "YES! I've never tasted that in a beer before."

4. Proceed with diacetyl rest :)

-Joe
 
The biggest reason not to it is that will lose residual CO2 and make bottle priming inaccurate. If it doesn't need it it is just a unnecessary step. I'm going to taste test it anyway.
 
The only thing I have heard against the D-rest is Noonan mentions that using a D-rest affects the flavor profile and looses some of the subtly and smoothness gained by lagering without one. So far I haven't found any details on why he says this, but maybe I should bring it up in the science arena???
 
Cpt_Kirks said:
+1


A "D Rest" will clean up a lot of nasty crap, other than diacetyl. I am yet to hear a reason NOT to do a rest. Lagers are more work and take a lot more time. A rest is just extra insurance.
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+1 to this...There's no reason not to, it won't harm your beer in anyway to do it

All you are doing is raising the temp in primary for 72 hours, sometime at the tail end of fermentation...I usually do it just before I am racking it to secondary in preparation to lager.

It's not like it's something so difficult to do....

Here's some great info on it https://www.homebrewtalk.com/f13/preventing-diacetyl-hold-butter-please-70438/
 
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.
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I wonder if a little shot of corn sugar added at the start of the rest would be in order?

I generally do the rest at 12 to 14 days.
 
Mine went from 1.060 to 1.026 when I started the rest. I raised it slowly over two days from 50F to 60F.

I'm not too concerned, since I'll be lagering this guy for at least 6 months.

-Joe
 
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.
Click to expand...

Does everyone agree about this? I've been doing a 3 day rest after 3 weeks in the primary, just before racking to lagering vessel.
 
I'm certainly not the authority on lagers, but I seem to recall that Kaiser has suggested that a diacetyl rest may be unnecessary if fermentation has completely finished and you've reached terminal gravity within a 'normal' time frame.

Same goes for the graduated cool-down to lagering temps. I also recall Kaiser just crashing it down.
 
Soperbrew said:
Does everyone agree about this? I've been doing a 3 day rest after 3 weeks in the primary, just before racking to lagering vessel.
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I never heard that before either, I usually do mine around 10-14 days, primarily because since I ghetto lager in the basement garage of my loft complex, I have to move the fermenter up 2 flights of stairs and across my building to my apartment. SO I just aim for around the 2 week mark, then prepare to secondary and lager.
 
A D-rest is only necessary when you have either a yeast that throws a large amount naturally, or you start your ferment at higher temps before lowering to your normal fermentation temps.

The timing seems to be rather important because once the edible sugars are gone, the yeast are not active enough to consume the larger amount of diacetyl that may be left. Even over the lager period, the yeast will not likely consume it.

This is all from Noonan. I don't have the book with me now, but I will reread it again tonight.

In many instances, a D-rest is unnecessary, and according to Noonan may adversely affect the beer, though as of yet I have found no explanation of why. Perhaps that is his anecdotal opinion.
 
The science behind the D-rest is hard to dispute. I have been reading extensively before jumping into the lager world, and the science makes things much more clear. A lot of opinion and guessing is eliminated when you look through the science glasses ;)
 
Boerderij_Kabouter said:
A D-rest is only necessary when you have either a yeast that throws a large amount naturally, or you start your ferment at higher temps before lowering to your normal fermentation temps.
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This is interesting. I pitched at 55F and still had a very obvious buttery taste and mouthfeel after a week. I wonder if the Wyeast 2633 is unusually diacetyl-producing?

-Joe
 
I just went back and reread the section in kalmeyer that I posted in the butter thread..

I highighted the section in method one about when one should do it...

"THE ROLE OF DIACETYL IN BEER
By Moritz Kallmeyer"

The Abstract begins...

Diacetyl as a product of fermentation is more characteristic of ales than lagers. Diacetyl is produced early in the fermentation, and then most of it is reabsorbed by the yeast and reduced to flavourless compounds later on. Yeast strains differ markedly in their diacetyl reduction ability. Some ales and a few lagers (such as the famous Pilsner Urquell) contain perceptible amounts of diacetyl, but as a rule modern brewers consider it as a fault. This is because certain bacterial infections and other errors in brewing technique will increase diacetyl levels resulting in unacceptable beer aroma and flavour profile. This parameter thus serves as a quality check. However, it is important to remember that diacetyl flavour is a natural by-product of yeast fermentation, and in some beer styles it is an optional or even required flavour component in low amounts.
Click to expand...

From here....


Drayman's Brewery and Distillery

There's two methods of rests listed in the Kallmeyer article...one for ales and warmer beers....interesting.

Maturation of beer flavour requires the presence of yeast as a catalyst. There are many methods of finishing that have the sole objective of prolonging the contact of beer with yeast after primary fermentation is completed. I want to emphasize that a diacetyl rest with most of the yeast lying at the bottom of the tank and not enough in suspension is of no use. Most lager breweries, especially those that use Weinhenstephan 308 or similar “diacetyl producing yeast’s” employ a long diacetyl rest, in order to minimize diacetyl in the finished beer.

Method 1
If a very cold primary fermentation was used it involves allowing the beer temperature to rise from the controlled primary fermentation temperature of about 10°C to 15-18°C when the primary fermentation is coming to an end. Normally, the time is determined by the attenuation of the beer. If, for example the wort starting gravity was 1050 and the expected terminal gravity is 1010, then the diacetyl rest would be commenced when the beer has attenuated to about SG 1023 when two-thirds of the total fermentable material in the wort has been consumed. The diacetyl rest normally lasts for 48-72 hours, until primary fermentation is over and secondary fermentation is under way. At this time the temperature is lowered when the more traditional method is followed, probably 1°C per day until the lagering temperature of 0-1°C is reached.

Method 2
If a warmer primary fermentation temperature was used for ale or lager the diacetyl rest involves either lowering the beer temperature 2 or 3°C at the end of primary fermentation or keeping it constant for up to 6 days. In lager yeast strains with low diacetyl production it is common practise nowadays to employ a short diacetyl rest followed by centrifuging to remove excess yeast and then crash cooling to 0°C. When brewing ales, that should have very low diacetyl levels especially German Ales like Alt and Kölsch, the implications are to not use highly flocculent yeast and to allow an extended primary fermentation, albeit at cooler temperatures until sufficiently low diacetyl levels are reached. Yeast that settles in the cone is still removed on a daily basis.
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Interesting for ALES one of the recomendations is to LOWER the temps a bit...or leave them at the same temp for 6 days...learns something new everyday...I'm going to have to try the cool rest.

It also backs up the idea of leaving beers on the yeastcake for awhile longer to allow the yeasts to clean up after themselves.
 
Boerderij_Kabouter said:
A D-rest is only necessary when you have either a yeast that throws a large amount naturally, or you start your ferment at higher temps before lowering to your normal fermentation temps.

The timing seems to be rather important because once the edible sugars are gone, the yeast are not active enough to consume the larger amount of diacetyl that may be left. Even over the lager period, the yeast will not likely consume it.

This is all from Noonan. I don't have the book with me now, but I will reread it again tonight.

In many instances, a D-rest is unnecessary, and according to Noonan may adversely affect the beer, though as of yet I have found no explanation of why. Perhaps that is his anecdotal opinion.
Click to expand...

Thanks for posting this, Justin. I'm being more and more convinced that homebrewers suffer from an abundance of neurotic ceremonials, repeating actions/procedures that have at least anecdotally proven unnecessary. In some circumstances, it seems that the diacetyl rest is becoming one of those.

Again, I'm not suggesting that performing a diacetyl rest is never useful, but rather it is one of diminishing returns in many circumstances as Noonan indicates. I don't have time to excerpt any passages now, but I plan on returning to this thread.

Jason
 
Actually, I think the yeast cake is of little to no use. It is the yeast that remains in suspension that are doing the work. Perhaps a swirl would help to resuspend some yeast.

Most lager fermentation schedules actually suggest dumping the yeast a few times throughout the fermentation.
 
I've been racking my lagers after just 8-10 days in the primary to a keg but I leave that keg at fermentation temps for at least a month...during which time the beer naturally carbonates as it finishes. If I were to do a D-rest that would be the perfect time to do it. TBH, I've never done a D-rest but I don't notice diacetyl in my beer (not saying it ain't there ;)). During the racking process into a warm keg, the beer and fridge warm up a bit but the beer is prob back to fermenting temp within 12 hours so I don't think that qualifies as a D-rest. But the main point is that there is still a ton of yeast in suspension so it can carbonate/finish/cleanup. Then into a lagering keg for the lagering.
 
I have done several Lagers in a row lately.

After 12-14 days in primary at about 50*F, I take the BB out of the cooler, give it a little shake to stir up the yeast, and sit it outside the cooler. The next day, I give the BB another little shake. After about 72 hours, I put the BB back in the cooler and drop the temp to the low 40's. I let it sit for about three or four days, until I am ready to keg.

All the Lagers I have done lately (since starting this method) have come out very nice, with no detectable diacetyl or other faults.

This may be a "neurotic ceremonial", but the beer is good. So, I will stick with it.

;)
 
No offense Cpt Kirks, but that is the kind of thing we are talking about. sorry.

The question is why do you do that? Is it actually helping? Why are you using that technique?

Yes, it may be producing good beer, but maybe there is a better way, or maybe it would be better if you didn't do the D-rest at all.

I think for most people, just following the lock-block-and-set idea is fine, but I am trying to push my brewing to a more controlled level so I can actually create what is in my minds eye. I see the D-rest as a tool that may or may not be beneficial, and its benefit must be directly related to how well it is used.
 
Boerderij_Kabouter said:
The question is why do you do that? Is it actually helping? Why are you using that technique?

Yes, it may be producing good beer, but maybe there is a better way, or maybe it would be better if you didn't do the D-rest at all.
Click to expand...

OK, I did several lagers with no D-rest. Over half had a diacetyl issue.

Now, I have done several lagers with the D-rest method listed above. I no longer have any traces of diacetyl, or other off flavors.

That tells me that a D-rest is a good thing. Now, if someone comes up with a better method to control off-flavors in lagers, I am game to try them out. Until then, I will neurotically keep doing the D-rest. Hell, I'm pretty OCD as it is.

Maybe we need somebody to do some split batch tests. One half the batch can be the control, with no D-rest, the other half with a D-rest. See if either half has diacetyl issues. The test will probably have to be run several times, with different recipes.

Based on my limited experience, I would bet darker lagers will be more prone to diacetyl issues.
 
What Noonan recommends is taking regular hydrometer readings once you feel you are getting close to the 2/3 mark. If you taste any trace of Diacetyl, then you do the rest. That is how he recommends doing it. Diacetyl has a very low taste threshold, so if there is any in the sample, you should be able to tell.

I know JZ recommends a lower starting temp, like 8ºF below your target temp, for pitching. This is consistent with Noonan in that low temps at the start of fermentation should limit the amount of diacetyl produced by the yeast during the respiration phase.

NOTE: I have not even done my first lager yet. I am just trying to get a good grasp of the process and how all the variables work together. My knowledge is just from books. Please don't take any offense, I am just trying to get to the bottom of some of these issues.
 
I've done only two lagers. The first with a D-rest the other with out it. Both are fine. I did pitch both cold, the second was in primary for a month under 50F then lagered at 40F in my BB (the coldest I could get it.)
 
Boerderij_Kabouter said:
The only thing I have heard against the D-rest is Noonan mentions that using a D-rest affects the flavor profile and looses some of the subtly and smoothness gained by lagering without one. So far I haven't found any details on why he says this, but maybe I should bring it up in the science arena???
Click to expand...

He does in fact propose two methods of achieving the same end result. the latter being our typical method of getting 75% through ferm and raising the temp.

The former involves step raising the temp after about 50% and involves skimming the krud. To this he attributes that silky smoothness.
 
Revvy said:
"THE ROLE OF DIACETYL IN BEER
By Moritz Kallmeyer"

"I want to emphasize that a diacetyl rest with most of the yeast lying at the bottom of the tank and not enough in suspension is of no use. "


It also backs up the idea of leaving beers on the yeastcake for awhile longer to allow the yeasts to clean up after themselves.
Click to expand...

Both in the same post. Wha?

Hey Reverand, been dipping a little too much in the Stoup have we?
 
Different lager yeasts produce different levels of diacetyl.

Diacetyl rests, if done and according to Noonan, should be done 6 points shy of target FG. IMO, ballparking this is OK, but better slightly early than slightly late. I do it as the krausen is falling. If you miss this window, you may as well not do one.

Allowing the beer to sit too long on primary yeast can result in off-flavors in the final beer due to decaying yeast cells.

A 6 month lagering period is rarely necessary IMO. Lagering times depend on the fermentability of the wort (dextrin content). One can be more than safe by doing 7 days for every 2°Plato (8 points of gravity). If the wort is very dextrinous (e.g., from a decoction), one could do 10 days for every 2°Plato.

I've not read anything against doing a D-rest. Kabouter, I'd be interested to know the Noonan reference (page) where he states they can have negative effects to try to figure out the context.
 
menschmaschine said:
Diacetyl rests, if done and according to Noonan, should be done 6 points shy of target FG. IMO, ballparking this is OK, but better slightly early than slightly late. I do it as the krausen is falling. If you miss this window, you may as well not do one.
Click to expand...

This has got to be the best reason not to. You would have to do a fast ferment test and take samples just about every day to do it correctly. Do it too early and it could effect the flavor. Do it too late and it does nothing but blow off CO2.
 
Diacetyl rests, if done and according to Noonan, should be done 6 points shy of target FG. IMO, ballparking this is OK, but better slightly early than slightly late. I do it as the krausen is falling. If you miss this window, you may as well not do one.
Click to expand...
6 pts. regardless of OG? Just curious. I've just been eyeballing it (no hydro reading or FFT) but thus far I'm just racking at that early stage for natural carbonation purposes...but I figure it would be the perfect time for a D-rest.

FWIW, I'm reading Noonan for the first time right now so if I come across the D-rest comment I'll post it and where it is. I'm just finishing the 'ingredients' section.
 
Conroe said:
This has got to be the best reason not to. You would have to do a fast ferment test and sake samples just about every day to do it correctly. Do it too early and it could effect the flavor. Do it too late and it does nothing but blow off CO2.
Click to expand...

I don't think this has to be exact. The point here is to catch the fermentation in enough time before it finishes. The highest risk timeframe for the production of flavor-active compounds in lager yeast at higher fermentation temperatures is early on. Once you're past the halfway point, this risk diminishes. Once you're 2/3 to 3/4 done, the risk is virtually nil. That's my understanding anyway. If you brew lagers frequently and have taken gravity readings during primary, you eventually learn, sort of intuitively, where the fermentation is by it's appearance and vigor (or lack thereof). So, that's why I always do them. It just cleans up the beer a bit.

SpanishCastleAle said:
6 pts. regardless of OG? Just curious. I've just been eyeballing it (no hydro reading or FFT) but thus far I'm just racking at that early stage for natural carbonation purposes...but I figure it would be the perfect time for a D-rest.
Click to expand...

That sounds alright to me.
 
Conroe,
I've been racking earlier than 1-2 pts. from OG. I took my info from Kaiser's Fermenting Lagers page...even though I don't do the recommended fast-ferment test (FFT).

From that page:
This (i.e. natural carbonation) can be achieved by:
racking the beer when about 1-2 % fermentable extract (4 - 8 gravity points) are left. At this time there is also enough yeast in suspension to ensure a good secondary fermentation. This process is called Gruenschlauchen (green racking) in German brewing.
Click to expand...

The 6 pts. Mensch recommended just happens to be smack dab in the middle.:)
 
menschmaschine said:
I've never carbed like that, so you may have a point there.

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

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.

It's entirely possible to bottle condition just like SpanishCastleAle does but with no pressure release there practically no margin for error. It's better to hit FG, raise the SG to calculated levels and then bottle. There would still be plenty of yeast in suspension at that time, they would be active for a day or two again and at warmer temperatures. What else is nessasry for a Daicetyl rest?
 
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?
 
drunkatuw said:
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?
Click to expand...

Here is how I fixed a batch like that:

Let the keg warm up. Make a nice starter with a neutral ale yeast, like US-05. Put the starter in the keg, and let it sit at room temp for a couple of weeks.

It probably won't eat all the diacetyl, but it should reduce it to a drinkable level.
 

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