When to do a diacetyl rest

[NewkyBrown]

A question for experienced lager brewers...

I pitched a gallon starter of Wyeast Oktoberfest yeast into my 1.06 marzen on monday am. I am holding the temp at a steady 50F.
There has been a steady krausen since.

I was wondering when to increase the temp for a diacetyl rest. Is there a certain time to do this? Should I take a gravity reading now or wait for a few more days.

Just wanted a rough idea. Thanks!

 

[h22lude]

Do you know what your cell rate per mL of wort per °P? For lagers, I pitch 2.5 million cells per mL of wort per °P. This is 1 million more than the online calculators suggest. I ferment in the high 40s and never do a d-rest. If you pitch enough yeast, you won't need a d-rest. if you pitch 1.5 million cells per mL of wort per °P like the calculators suggest, then I would recommend a d-rest. Do it with 1.5°P left (about 4 or 5 gravity points).

 

[springinloose1]

If you pitch enough yeast, you won't need a d-rest.

That's the first time I've heard this approach h22lude. I've always done a d-rest with a lager. Diacetyl is a byproduct of fermentation that needs to be addressed when doing lagers. You don't need to do a d-rest if it's an ale, but because lager yeast is fermented down low, you'll need to raise the temp so the yeast can clean up the diacetyl its produced during fermentation.

Lagers are my primary jam nowadays. A safe timetable if you're not going to continuously pull gravity samples is to leave it in primary 2 weeks, raise to 60-62 degrees for 2-3 days for your d-rest, transfer to secondary, roll down to 55 for a couple days then every couple days click the temp down 2-3 degrees until you reach 33 and hold for two weeks. Or if you are ambitious enough to keep yanking samples, wait until you're about 5-10 points away from your targeted FG then raise temps. A light German Pils will be ready for a d-rest before a Doppelbock but I'm lazy and have stuck with that timetable and had zero detectable diacetyl in about 25 lager batches.

P.s - You didn't dump a gallon starter into that precious Oktoberfest right? Only the slurry.

Cheers!

 

[dmtaylor]

When gravity points are half of what you started with, safe to do the D rest. So for your example, when 1.060 becomes 1.030, raise the temperature. Easy peasy.

 

[h22lude]

If you pitch enough yeast, you won't need a d-rest.

That's the first time I've heard this approach h22lude. I've always done a d-rest with a lager. Diacetyl is a byproduct of fermentation that needs to be addressed when doing lagers. You don't need to do a d-rest if it's an ale, but because lager yeast is fermented down low, you'll need to raise the temp so the yeast can clean up the diacetyl its produced during fermentation.

I highly suggest you try it. I just did a lighter pilsner this way. I pitched 2.5 million cells per mL of wort per °P which is about 700B. That's almost double what the calculators recommend. I fermented for about 5 days at 48°F then transferred to a keg with a spunding valve with 1.5°P left. I let it finish fermenting at 48°F (maybe 4 days) and carbonate at the same time using the CO2 produced by the yeast. Then I lagered for almost 2 weeks at 30°F. Came out perfect.

 

[jodell]

Not needing a d-rest is YEAST DEPENDENT!

(Sorry I yelled)

I say this because I think it's bad advice to say if you pitch enough you'll never need a d-rest. Some YEAST are notorious for never producing diacetyl, others are notorious for producing lots of it.

No one strain is alike. If you have a diacetyl problem, within 5 gravity points is a good time to start bumping it up. Personally I don't see why anybody wouldn't bump up towards the end just to help finishing anyways.

Diacetyl is going to be produced whether you pitch 10% of the recommended value or 10,000%, but it's all dependent on the specific strain, amounts, and can you detect it

 

[FloppyKnockers]

Easy answer: 2 weeks in for 3 days at room temp then start lagering.

 

[NewkyBrown]

Appreciate everyone’s input. I’ll check the gravity this weekend and get an idea.
I didn’t work out cell counts, just made a big starter and fresh yeast.
Oh and I did decant!

 

[h22lude]

Not needing a d-rest is YEAST DEPENDENT!

(Sorry I yelled)

I say this because I think it's bad advice to say if you pitch enough you'll never need a d-rest. Some YEAST are notorious for never producing diacetyl, others are notorious for producing lots of it.

No one strain is alike. If you have a diacetyl problem, within 5 gravity points is a good time to start bumping it up. Personally I don't see why anybody wouldn't bump up towards the end just to help finishing anyways.

Diacetyl is going to be produced whether you pitch 10% of the recommended value or 10,000%, but it's all dependent on the specific strain, amounts, and can you detect it

I haven't found this to be true in my experience. I have used yeast that others have said they got a lot of diacetyl and I did get any with the pitch rate I use.

 

[Upthewazzu]

I don't generally pull gravity samples, but my method is to start raising the temp by 3°F at day 6 or 7. So if I start fermenting at 50°, I'll hit 65° by day 12 or so. leave it there for 48 hours and then crank back down to ~45°. Add gelatin and then drop to ~35°, keg and then lager at 35° for however long it takes to open up space in the beer fridge.

 

[jodell]

Do you have anything else to back that up with? I'm sorry but I think that's a bold statement to say you should never have diacetyl in your beer if you almost double pitch and your biggest argument is "I didn't taste it"

I don't mean to sound rude here but I judge quite a bit of beers and I taste a lot of lagers with diacetyl. While I can't say I have ever a pitched as much as you are claiming, (although I did pitch one with wlp Oktoberfest blend at 2.25million and still had to do a diacetyl rest) I still don't see how saying pitch more and don't worry about it is good advice... diacetyl is going to be produced when pitched. Ales are are already at d-rest temps so they get cleaned up quick, however, I believe (with my experience) lagers almost always need to have a d-rest.

I haven't found this to be true in my experience. I have used yeast that others have said they got a lot of diacetyl and I did get any with the pitch rate I use.

 

[h22lude]

Do you have anything else to back that up with? I'm sorry but I think that's a bold statement to say you should never have diacetyl in your beer if you almost double pitch and your biggest argument is "I didn't taste it"

I don't mean to sound rude here but I judge quite a bit of beers and I taste a lot of lagers with diacetyl. While I can't say I have ever a pitched as much as you are claiming, (although I did pitch one with wlp Oktoberfest blend at 2.25million and still had to do a diacetyl rest) I still don't see how saying pitch more and don't worry about it is good advice... diacetyl is going to be produced when pitched. Ales are are already at d-rest temps so they get cleaned up quick, however, I believe (with my experience) lagers almost always need to have a d-rest.

I do believe I read a quote from a professional brewing literature that explained this but I will need to find it. I do know other people brewing lagers this way with no diacetyl in any of their lagers (and they brew mostly lagers). I think the reason you taste a lot of diacetyl in lagers when judging is because people don't pitch enough yeast.

I've used some yeasts that people say produce a lot of diacetyl but I get now pitching high. The others I know that brew with a high pitch rate for lagers never get diacetyl. I don't think it is just luck.

With a higher pitch rate, diacetyl is produced quicker which means the yeast are still pretty active. Also with a higher pitch rate, diacetyl reduction happens quicker. I bet if I sampled my beers at the right time, I would taste diacetyl but because of the high pitch rate it is cleaned up pretty quickly.

From the Journal of the Institute of Brewing "As expected, increasing the pitching rates led to faster fermentation rates and higher yeast cell counts. Formation of 2-methyl-1-propanol increased with increasing pitching rate, but the formation of 2- and 3-methyl-1-butanol decreased. The pitching rate did not alter ester formation in these experiments, with the exception of isoamyl acetate, where the level declined with an increased pitching rate. Lower pitching rates led to higher levels of diacetyl and 2,3-pentanedione. The effect of pitching rate on flavour compounds clearly merits further investigation."

 

[jodell]

I do believe I read a quote from a professional brewing literature that explained this but I will need to find it. I do know other people brewing lagers this way with no diacetyl in any of their lagers (and they brew mostly lagers). I think the reason you taste a lot of diacetyl in lagers when judging is because people don't pitch enough yeast.

I've used some yeasts that people say produce a lot of diacetyl but I get now pitching high. The others I know that brew with a high pitch rate for lagers never get diacetyl. I don't think it is just luck.

With a higher pitch rate, diacetyl is produced quicker which means the yeast are still pretty active. Also with a higher pitch rate, diacetyl reduction happens quicker. I bet if I sampled my beers at the right time, I would taste diacetyl but because of the high pitch rate it is cleaned up pretty quickly.

From the Journal of the Institute of Brewing "As expected, increasing the pitching rates led to faster fermentation rates and higher yeast cell counts. Formation of 2-methyl-1-propanol increased with increasing pitching rate, but the formation of 2- and 3-methyl-1-butanol decreased. The pitching rate did not alter ester formation in these experiments, with the exception of isoamyl acetate, where the level declined with an increased pitching rate. Lower pitching rates led to higher levels of diacetyl and 2,3-pentanedione. The effect of pitching rate on flavour compounds clearly merits further investigation."

You are right on the beers I judge and I did not intend to say that all the beers I judge are pitched properly.

And I absolutely will agree that higher pitching rates will lead to less produced. But it will still be produced and a lot of the lagers I make (I make a lot of lagers myself) still need a diacetyl rest (I will say I am extremely sensitive to diacetyl)

I personally am one to argue that pitching to much yeast also causes other problems...but that is for a different thread!

 

[jjr999]

I wrote this based on Wolfgan and Kunze to help me understand it better.

First the yeast forms pyruvic acid then acetohydroxy acids from that during respiration and fermentation. Their formation is dependent on:

1. Yeast strain.
2. Yeast pitching rate - more yeast leads to more acetohydroxy acids but also faster and more complete removal.
3. Oxygen - Oxygen leads to increased acetohydroxy acids, especially at first few days of fermentation.


However none of these factors are strong enough so that production of acetohydroxy acids can be altered by playing with them.

Next, the acetohydroxy acids create vicinal diketones diacetyl when the they create CO2. This conversion is dependent on:

1. pH - a pH of 4.3 is optimal, and the conversion decreases as pH increases.
2. temperature - increased conversion with increased temperature
3. oxygen - more oxygen, more conversion

Finally the diacetyl is removed by the yeast cells. Going from Diacetyl to acetoin to butanediol, which can't be tasted.
The removal of diacetyl is dependent on:
1. Longer primary fermentation - more contact time with yeast
2. Yeast strain doesn't matter at this point.
3. Temperature increases greatly increase removal (about 3x as effective going from 8c to 18c)
4. Yeast concentration, so things that keep the yeast from settling, like pumping, pressure release, movement etc increase removal.
5. Kraunsening helps - yeast removal power is at it's strongest when the yeast is multiplying the fastest.

It's important to note that as the fermentation attenuates. Increases in oxygen (i.e racking, moving etc) will increase diacetyl, which then needs to be removed. If this is late in the fermentation, say from primary to secondary where there is less yeast, it will be harder for the yeast to remove it. So be very, very careful not to oxygenate after the primary.

 

[h22lude]

You are right on the beers I judge and I did not intend to say that all the beers I judge are pitched properly.

And I absolutely will agree that higher pitching rates will lead to less produced. But it will still be produced and a lot of the lagers I make (I make a lot of lagers myself) still need a diacetyl rest (I will say I am extremely sensitive to diacetyl)

I personally am one to argue that pitching to much yeast also causes other problems...but that is for a different thread!

Have you tried any other lagers at 2.5m/mL/°P other than that WLP 820?

My schedule is ferment at 48°F until 1.5°P left. Transfer to keg with spunding valve and let ferment out. Once complete, I lager until I feel like it is ready. This pilsner that I am drinking right now was lagered for almost 2 weeks. Right about 3 weeks grain to glass and it is delicious.

I wrote this based on Wolfgan and Kunze to help me understand it better.

First the yeast forms pyruvic acid then acetohydroxy acids from that during respiration and fermentation. Their formation is dependent on:

1. Yeast strain.
2. Yeast pitching rate - more yeast leads to more acetohydroxy acids but also faster and more complete removal.
3. Oxygen - Oxygen leads to increased acetohydroxy acids, especially at first few days of fermentation.


However none of these factors are strong enough so that production of acetohydroxy acids can be altered by playing with them.

Next, the acetohydroxy acids create vicinal diketones diacetyl when the they create CO2. This conversion is dependent on:

1. pH - a pH of 4.3 is optimal, and the conversion decreases as pH increases.
2. temperature - increased conversion with increased temperature
3. oxygen - more oxygen, more conversion

Finally the diacetyl is removed by the yeast cells. Going from Diacetyl to acetoin to butanediol, which can't be tasted.
The removal of diacetyl is dependent on:
1. Longer primary fermentation - more contact time with yeast
2. Yeast strain doesn't matter at this point.
3. Temperature increases greatly increase removal (about 3x as effective going from 8c to 18c)
4. Yeast concentration, so things that keep the yeast from settling, like pumping, pressure release, movement etc increase removal.
5. Kraunsening helps - yeast removal power is at it's strongest when the yeast is multiplying the fastest.

It's important to note that as the fermentation attenuates. Increases in oxygen (i.e racking, moving etc) will increase diacetyl, which then needs to be removed. If this is late in the fermentation, say from primary to secondary where there is less yeast, it will be harder for the yeast to remove it. So be very, very careful not to oxygenate after the primary.

Nice info...and for your first post at that

 

[jodell]

Have you tried any other lagers at 2.5m/mL/°P other than that WLP 820?

My schedule is ferment at 48°F until 1.5°P left. Transfer to keg with spunding valve and let ferment out. Once complete, I lager until I feel like it is ready. This pilsner that I am drinking right now was lagered for almost 2 weeks. Right about 3 weeks grain to glass and it is delicious

I've done big pitch rates with many strains, and some have turned out without a trace of diacetyl, but I think you are missing my point, either that or I am missing yours.

I am saying that production of diacetyl is very dependant on yeast strain. The amount you pitch and temps you ferment will influence the amount for sure.
As you know yeast is a living organism, and each strain will behave differently, so I do not believe that every strain will follow the same patterns. I have had some that I pitched lower (around 1.5m) that fermented fine (w34/70) and some that i pitch large quanities (while I do not recall ever pitching as much as 2.5m) that still produced a good amount and needed a d rest. Every strain will ferment and produce off flavors very differently.

 

[h22lude]

I've done big pitch rates with many strains, and some have turned out without a trace of diacetyl, but I think you are missing my point, either that or I am missing yours.

I am saying that production of diacetyl is very dependant on yeast strain. The amount you pitch and temps you ferment will influence the amount for sure.
As you know yeast is a living organism, and each strain will behave differently, so I do not believe that every strain will follow the same patterns. I have had some that I pitched lower (around 1.5m) that fermented fine (w34/70) and some that i pitch large quanities (while I do not recall ever pitching as much as 2.5m) that still produced a good amount and needed a d rest. Every strain will ferment and produce off flavors very differently.

Fair enough. I probably should have ended my original post with, YMMV. I have yet to have any diacetyl detected but I also haven't used every lager yeast. I'd like to find one that produces a lot of diacetyl and test my procedure.

 

[Morrey]

Great discussion, and like all valuable learning experiences, learning often means we challenge the "norm" and each other.

I am not a judge but have often wanted to know what issues and off flavors are plaguing other brewers. Did I read there is an off flavor kit that I can order giving me a chance to learn more about this? If so, is there a place to order a kit?

 

[dmtaylor]

I am not a judge but have often wanted to know what issues and off flavors are plaguing other brewers. Did I read there is an off flavor kit that I can order giving me a chance to learn more about this? If so, is there a place to order a kit?

Diacetyl is a very common off-flavor that occurs a lot with lagers. Oxidation is common with all beers. Other off-flavors are still fairly common but not nearly as much as those two.

There are off-flavor test kits available, you can look around. BJCP sells them only to judges ranked Recognized or higher, see here for details:

http://dev.bjcp.org/education-training/education-resources/sensory-kits/

 

[Morrey]

Fair enough. I probably should have ended my original post with, YMMV. I have yet to have any diacetyl detected but I also haven't used every lager yeast. I'd like to find one that produces a lot of diacetyl and test my procedure.

I'm proposing a question that is probably just as true with beer tasting and evaluations as it is with BBQ for which I once conducted judging classes:

Some folks are extremely sensitive to certain flavors while others are not. A personal example is that I can strongly detect cumin in micro doses while other folks may not be able to detect cumin at this level at all. I suppose the same may be true of perhaps diacetyl? If a taster or beer judge has a particular sensitivity for diacetyl, is it possible that others may not detect this flavor at all?

Of all the beers I have made, I cannot say I have ever detected diacetyl. Is it that I have just been lucky, or maybe my brewing practices are sound....or maybe I just don't have a sensitivity for this off flavor and it is there?

 

[h22lude]

I'm proposing a question that is probably just as true with beer tasting and evaluations as it is with BBQ for which I once conducted judging classes:

Some folks are extremely sensitive to certain flavors while others are not. A personal example is that I can strongly detect cumin in micro doses while other folks may not be able to detect cumin at this level at all. I suppose the same may be true of perhaps diacetyl? If a taster or beer judge has a particular sensitivity for diacetyl, is it possible that others may not detect this flavor at all?

Of all the beers I have made, I cannot say I have ever detected diacetyl. Is it that I have just been lucky, or maybe my brewing practices are sound....or maybe I just don't have a sensitivity for this off flavor and it is there?

I was thinking this as well. I think the only way to know is if you judge a beer and detect diacetyl but all the other judges don't. Good chance, that judge is more sensitive to it since the other judges didn't taste it. Another option is to buy an off flavor kit and add just enough of the off flavor to be right over the threshold of what a "normal" person can taste.

 

[Morrey]

I was thinking this as well. I think the only way to know is if you judge a beer and detect diacetyl but all the other judges don't. Good chance, that judge is more sensitive to it since the other judges didn't taste it. Another option is to buy an off flavor kit and add just enough of the off flavor to be right over the threshold of what a "normal" person can taste.

I had asked about one of those off flavor kits, and Dave Taylor responded to say I'd have to be in the BJCP program at a certain level to have this kit available. Since I'm not in the program, If anyone knows where I might find one I feel this knowledge would enhance my skills as a brewer.

 

[h22lude]

I had asked about one of those off flavor kits, and Dave Taylor responded to say I'd have to be in the BJCP program at a certain level to have this kit available. Since I'm not in the program, If anyone knows where I might find one I feel this knowledge would enhance my skills as a brewer.

If you have any competitions near you or a local club, ask around. Someone should be willing to help you out.

 

[Nebraskan]

So what happens if you pitch a lot of lager yeast starter, and ferment at higher temps? I made up a Munich Dunkel last Saturday, pitched the yeast that night. Sunday it was going strong. Monday and Tuesday very strong. OG was 1.052 using S-23 Lager yeast. Closet it was in was 70 F. Racked it off main yeast Wed and the SG was 1.0093 Pretty much done, although it is still doing a bit of off gassing.

The only way I could do a diacetyl rest would be to re-pitch some yeast and add just a bit of maltose to feed those yeasts as they are being stirred up in the beer.