Diacetyl Rests

[BeaverBarber]

I'm not usually this paranoid, but I've never tasted diacetyl quite as powerful as this...unless you count movie popcorn. I'm sure it'll be fine. Thanks all. I'll wait it out.

Mike

[dstar26t]

At a brew pub I volunteer at, I witnessed diacetyl removal within 8 hours. We took a sample of their Vienna Lager in the morning to check for diacetyl and to see if it had hit terminal gravity yet. It was full of diacetyl. We took another sample at the end of the day and it was gone. It blew my mind. Unfortunately, I don't know what day of fermentation that was. I believe they use the Budvar yeast as well and it wasn't quite at terminal yet.

[BeaverBarber]

So a week after my 58 degree diacetyl rest created a true diacetyl bomb, the beer has been sitting at 52 degrees, and the diacetyl is almost completely gone; I can't smell it, and I can only occasionally taste it in the sample. From what I've read, most breweries wait 3-4 weeks after fermentation is complete to crash cool, and that's totally dependent on the presence of diacetyl. I'll probably wait another week and a half. The beer reminds me of Sierra Nevada Summerfest, but it's not quite as good yet. Here's what I've learned:

1. Alpha acetolactate is tasteless and odorless; diacetyl is not.
2. In lagers, the purpose of a diacetyl rest isn't to remove diacetyl; it's purpose is to rapidly convert alpha acetolactate into diacetyl. It's better if you control this process than to allow it to happen naturally over time.
3. Don't just start dropping your temperature after fermentation is complete and you've completed a 2-3 day diacetyl rest; that's dogma, and it's wrong.
4. Yeast is the only thing that'll clean up your diacetyl, so do like the big brewers do: Taste your beer before dropping your yeast...sterile turkey basters work great. Most large breweries won't drop their temperatures, and subsequently their yeast, until after all the diacetyl is gone, and unless you're beechwood aging, that's about 3-4 weeks after fermentation is complete.
5. The "diacetyl test", where you heat your beer up to 140 F, cool down, and compare to an original sample, doesn't tell you the current diacetyl content in your beer; it tells you what your beer will eventually taste like once the alpha acetolactate has converted. That conversion happens naturally over time and nothing can stop it. So unless you like the taste of the heated and cooled sample, you'll have to wait some more. You could try another diacetyl rest to speed things up.

Enjoy your pilsners!

[BrewerJ]

So a week after my 58 degree diacetyl rest created a true diacetyl bomb, the beer has been sitting at 52 degrees, and the diacetyl is almost completely gone; I can't smell it, and I can only occasionally taste it in the sample. From what I've read, most breweries wait 3-4 weeks after fermentation is complete to crash cool, and that's totally dependent on the presence of diacetyl. I'll probably wait another week and a half. The beer reminds me of Sierra Nevada Summerfest, but it's not quite as good yet. Here's what I've learned:

1. Alpha acetolactate is tasteless and odorless; diacetyl is not.
2. In lagers, the purpose of a diacetyl rest isn't to remove diacetyl; it's purpose is to rapidly convert alpha acetolactate into diacetyl. It's better if you control this process than to allow it to happen naturally over time.
3. Don't just start dropping your temperature after fermentation is complete and you've completed a 2-3 day diacetyl rest; that's dogma, and it's wrong.
4. Yeast is the only thing that'll clean up your diacetyl, so do like the big brewers do: Taste your beer before dropping your yeast...sterile turkey basters work great. Most large breweries won't drop their temperatures, and subsequently their yeast, until after all the diacetyl is gone, and unless you're beechwood aging, that's about 3-4 weeks after fermentation is complete.
5. The "diacetyl test", where you heat your beer up to 140 F, cool down, and compare to an original sample, doesn't tell you the current diacetyl content in your beer; it tells you what your beer will eventually taste like once the alpha acetolactate has converted. That conversion happens naturally over time and nothing can stop it. So unless you like the taste of the heated and cooled sample, you'll have to wait some more. You could try another diacetyl rest to speed things up.

Enjoy your pilsners!

The purpose of a diacetyl rest is to reduce the total diacetyl level in the beer. If it was just to convert alpha acetolactate into diacetyl then you would be left with buttered popcorn. Warming the beer up will convert alpha actolactate into diacetyl and also speed up the yeasts ability to reabsorb the diacetyl. Depending on yeast strain and your fermentation practices a diacetyl rest isn't allways necessary. I have brewed several lagers that have never been above 52, it just takes a little longer for the yeast to do their thing.

Sounds like your lager cleaned itself up. Now drink up and brew another lager while you have a large healthy pitch.

[BeaverBarber]

There are many different approaches to reducing diacetyl in a lager. Tasty uses what's called a Narziss method of lager fermentation, where he waits until 50% of the fermentation is complete, and then raises the temperature of his fermentation to ale temperatures which will get rid of the diacetyl. Another method is to allow the beer to stay at a constant temperature, and that will work if the yeast flocculation is low enough to stay in suspension until the work is complete otherwise you might have to kraeusen your beer for better diacetyl reduction as well as better attenuation of the beer. Because I've selected a med-high flocculating yeast strain, I've chosen the route of a 2 day diacetyl rest to speed the conversion of alpha acetolactate to diacetyl, and a lengthy maturation process at 52 degrees in hopes of being able to clean up the byproducts of fermentation before my yeast drops out of suspension; most notably diacetyl. I did so with the understanding that I still may have to kraeusen the beer for complete diacetyl reduction. Once diacetyl is no longer present, I can transfer the beer and crash cool to allow for the yeast and haze causing protiens to drop out of solution. I think the main problem with people's understanding of diacetyl reduction in lager brewing goes back to John Palmer's free online resource that we all know, love, and like to quote. If you type "diacetyl rest" into a search bar, it's the first thing that pops up. He writes under lager brewing, "To remove any diacetyl that may be present after primary fermentation, a diacetyl rest may be used. 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. This makes the yeast more active and allows them to eat up the diacetyl before downshifting into lagering mode." Depending on how you interpret this, and unless his "downshift to lagering mode" doesn't go much below suggested fermentation temperatures, he's left out the 3-4 week maturation process at a temperature where yeast can still actively metabolize unwanted fermentation by products; albeit very slowly. To read that I would believe that if you just raise the temperature of your lager for a couple of days after you hit terminal gravity, all of the diacetyl will be gone, and all that's left to do is transfer, crash cool for a week, and serve. Interpreted literally, that's bad information. I really don't want to come across as a pompous know-it-all because I run into those types of people every day, and I genuinely can't stand them. I like to take shots at them in real life, and even occasionally on this message board. I really am trying to share information to help out with a poorly understood process. I can't wait to harvest my yeast and try this again using the Narziss (Tasty) method because I'm curious how that works out.

[brewinhard]

I have been having good luck with pitching my lagers around 48F. 90 seconds of O2 with a .5 micron stone. I then ferment (based on OG) at 48-49F for about 7-9 days. When the krausen starts to drop back into the beer, I slowly raise the ferment temps by 2 deg./day until I reach about 65F. Then I take it out of the fridge and bring it inside my house to clean up any remaining diacetyl (if there even is any, I have not picked up any myself) for 2-3 days at room temps (68-70F). I then crash cool for about 2 days, then closed transfer to a keg. Lager 4-6 weeks depending on style, carbonate and ENJOY DAILY!!

[BeaverBarber]

I have been having good luck with pitching my lagers around 48F. 90 seconds of O2 with a .5 micron stone. I then ferment (based on OG) at 48-49F for about 7-9 days. When the krausen starts to drop back into the beer, I slowly raise the ferment temps by 2 deg./day until I reach about 65F. Then I take it out of the fridge and bring it inside my house to clean up any remaining diacetyl (if there even is any, I have not picked up any myself) for 2-3 days at room temps (68-70F). I then crash cool for about 2 days, then closed transfer to a keg. Lager 4-6 weeks depending on style, carbonate and ENJOY DAILY!!

That's exactly what I want to try except the closed transfer to a keg because I didn't think of that. Are you filtering at the same time? Do you think that filtering will hurt the lagering process? Logic tells me that the yeast usefulness has run its course, and it will actually help get rid of some of the haze causing proteins. Thanks for sharing your process.

[ScottyB-Brewing]

You guys seem to be talking about lagers but I have been getting diacetyl taste with the past 5 pale ales I've done, I haven't done the diacetyl test but I have let all of'em sit in the carboy for at least 2 weeks and raised the temp a few degrees at the end.

My solution, no more pale ales, I never get diacetyl with any other beer I brew