Diacetyl Rest and Lagering

Discussion in 'Homebrewing' started by OldBrewer, Apr 19, 2018.

  1. OldBrewer

    OldBrewer Aspirant (245) Jan 13, 2016 Ontario (Canada)

    Although these two subjects have been addressed many times, there are some aspects that seems to have been missed. I realize that there are many opinions on whether or not a diacetyl rest should be done in the first place, but I don't want to get into that debate in this thread. I just want to be clear on what the recommended process for doing a diacetyl rest is, if one were to decide to do one.

    In his book Yeast, Chris White suggests that a diacetyl rest should be done when the lager is 2-5 specific gravity points before reaching terminal gravity. The temperature of the lager should then raised into the 65-68 F range for a two day period. He then suggests that the temperature of the beer should be lowered to encourage flocculation of any remaining yeast. He then discusses whether the beer should be crashed to lagering temperatures or whether the temperature should be lowered slowly. He answers by saying that below 40 F, very little happens. Thus once you reach 40 F you can crash it to the desired cold conditioning temperature at or near freezing temperature. He also says that if you want the yeast to be active and carry on reduction of fermentation by-products, it happens much faster at higher temperatures.

    He says, however, that very rapid reduction in temperature (less than 6 hours) at the end of fermentation can cause the yeast to excrete more ester compounds instead of retaining them. Also, if you plan on repitching the yeast, you should avoid very rapid temperature changes. He says that after fermentation slows and the yeast begins to flocculate, the brewer should start to slowly cool his beer at a rate of 1-2 F (0.5-1 C) per day in order to avoid sending the yeast into dormancy. "After a few days", the beer has reached a temperature close to 40F (4 C) but there are still some fermentable sugars remaining. The brewer then transfers the beer into the lagering container (e.g. keg). He says the yeast needs to remain active for a long time in order to reduce any fermentation by-products. He therefore leaves one guessing how long the beer should remain at 40 F before crashing to cold conditioning temperature.

    Having read all this, I realized that he didn't explain his process very thoroughly, and left a lot of questions unanswered. Here are some of the questions I had:

    1. When you raise the temperature near the end of fermentation to 65-68 F (I assume by taking the keg out of the kegerator and placing it directly in a room at that temperature), wouldn't that rapid increase in temperature over such a short period of time (perhaps a day?) result in the shocking of the yeast?

    2. Once you have completed the two day diacetyl rest, you then bring it back down to the initial fermentation temperature and slowly reduce the temperature by 1-2 F per day until "after a few days" it reaches 40 F (this implies that the beer was initially already at the fermentation temperature (e.g. approx. 47-55 F). Chris White failed to mention whether this slow reduction in temperature also applies to bringing it down from 65-68 F to the initial fermentation temperature. His logic would seem to apply, although at 50 F fermentation temperature, it would take about 8-16 days, and an additional 5-10 days to get it to 40 F. A total of 13-26 days!!! So does Chris mean to crash it down to fermentation temperature (wouldn't that shock the yeast?), or to lower it gradually a degree or two a day?

    3. Chris White says that the yeast are still active at 40F and need to remain active "for a long time". So, how long does he suggest that the beer should remain at 40 F before crashing to cold conditioning temperature? With what he seems to imply, I can see it taking a month or more after fermentation is almost finished before it can even be cold-conditioned.

    I would be most appreciative of any comments or suggestions.

    (P.S. I did write to White Labs concerning these questions, but did not get a reply).
  2. Brewday

    Brewday Initiate (108) Dec 25, 2015 New York

    I think it's more important when you slowly lower the temp after d-rest then worrying about the temp free rising.The one i have now I let it free rise to mid 60s with 1-2 points left for a few days then lowered 5 degs a day to 34 and it taste great. I also used 2 packets of m-84 so that also helps.
    PortLargo and OldBrewer like this.
  3. VikeMan

    VikeMan Meyvn (1,453) Jul 12, 2009 Pennsylvania

    A day (or however long it takes) won't shock the yeast. It takes a while for (mostly) water to come up to temp, and yeast are not nearly as sensitive to sudden increases in temp as they are to sudden decreases. (And again, this scenario is not sudden.)

    I can't say exactly what White meant, but in my experience, 1-2 degrees per day is probably very conservative. I have gone at least 4-5 degrees per day. "Shock" is really what happens when you dump yeast directly into a large volume of cold liquid. I'm not sure if a fermentation fridge could actually shock the post fermentation yeast in a 5 gallon batch of beer starting at 65-68. And I think it might have been Jamil that said something like...once yeast have finished active fermentation, they're not nearly as susceptible to thermal shock as they are during fermentation.

    First, 40F actually is a lagering/cold crashing temperature. I'm not sure what this is about. I go from from diacetyl rest temps down to 40 fairly quickly (4-5 degrees per day), and then lager/crash at 40F.
    OldBrewer likes this.
  4. OldBrewer

    OldBrewer Aspirant (245) Jan 13, 2016 Ontario (Canada)

    That makes more sense than how it is explained in the book. At what point do you rack it off the yeast?
  5. VikeMan

    VikeMan Meyvn (1,453) Jul 12, 2009 Pennsylvania

    I normally transfer to secondary (a corny keg) as soon as the D-Rest is finished.
  6. OldBrewer

    OldBrewer Aspirant (245) Jan 13, 2016 Ontario (Canada)

    Wouldn't you get more precipitants/flocculation by first lowering it down to about 50 F before transferring?
  7. JackHorzempa

    JackHorzempa Poo-Bah (3,637) Dec 15, 2005 Pennsylvania

    I have followed the writings of Bill Pierce on lagering my beers to good effect (see link below).

    I have brewed about 50 batches of lager and I have never conducted a diacetyl rest. My palate is very sensitive to diacetyl and I have never perceived any diacetyl in my lagers. If I was to conduct a diacetyl rest (but I personally never would):

    For homebrewers this typically means letting the fermenter warm to room temperature for a couple of days. Not all lager strains produce significant amounts of diacetyl, but unless you have previous experience with the yeast you are using, it is best to perform the rest anyway, as it does no harm. Conduct the rest in the primary fermenter in order to maximize the yeast population and quickly reduce the diacetyl.”

    I personally cold crash my lagers after I transfer from the primary to the secondary and this process has always worked for me:

    “Some brewing texts recommend slowly reducing the temperature by no more than 5 °F (3 °C) per day until the temperature is at the desired setting for lagering. However, many homebrewers ignore this advice and achieve excellent results. There is agreement that in order to achieve the maximum effect the lagering needs to be done cold, with the temperature no more than 40 °F (5 °C). Many commercial breweries lager at nearly freezing temperatures, in the 32–34 °F (0–1 °C) range.”


    OldBrewer likes this.
  8. VikeMan

    VikeMan Meyvn (1,453) Jul 12, 2009 Pennsylvania

    Yes. OTOH, their is a great belief (if not quantifiable evidence?) that yeast play a role in the magic that happens during lagering. So the answer to this conundrum, like many in brewing, involves assessing a tradeoff and picking your poison.
    warchez and OldBrewer like this.
  9. OldBrewer

    OldBrewer Aspirant (245) Jan 13, 2016 Ontario (Canada)

    Very good point! I'm sold :-)
  10. OldBrewer

    OldBrewer Aspirant (245) Jan 13, 2016 Ontario (Canada)

    No more than 40 F seems to agree with what Chris White said, although he also suggested that at some point it should be brought down to near freezing for the cold conditioning stage. Thus both points above seem to make sense. The real question this begs though, is how long should it lager at or above 40 F before crashing it to near freezing? I have never seen this addressed. Chris White seems to suggest "a long time".
  11. JackHorzempa

    JackHorzempa Poo-Bah (3,637) Dec 15, 2005 Pennsylvania

    I have looked for 'science' related to what you are asking here but I have not found any technical journal articles. If you ever succeed here please let me know.

    I can relate to you that I personally do not do a 40+ lagering and then near freezing phase. I place my secondary in my lagering chamber and lager for about 5 weeks for a temperature in the mid- 30's F. This works for me. The resulting beer has no off flavors (i.e., no acetaldehyde as one example) and it has the crisp/clean quality that I desire in a lager beer.

    There are likely differing schemes to achieve the qualities desired of a lager (lagering) beer. The above scheme is what works for me.


    P.S. FWIW I have a Kolsch in my lagering chamber right now (at the three week mark at the moment).
  12. OldBrewer

    OldBrewer Aspirant (245) Jan 13, 2016 Ontario (Canada)

    I have searched for months and cannot find anything other than variations of the information I provided above. I would think that Chris White would have the science and laboratory to confirm what he says, although he leaves out a lot in his explanation. I did write to his lab a week or so ago, but have not heard back. If I do, and can provide the response here.

    This whole lagering thing seems to be very dependent on the yeast, and therefore crashing the beer may not be the best thing to do. Apparently there's a lot of chemistry that's taking place during lagering, so the yeast must be healthy enough to do what they need to do. I'm currently using a lager yeast that I'm not too familiar with, so I intend to do a rest with it. I find that the rest also speeds things up in terms of yeast activity. I have seen some of my past lagers continue to ferment for weeks, but when I do a rest, the visible activity mostly stops after the rest.

    Chris White seems to be very emphatic about the 40 F mark, although he does not really explain why. I understand that yeast continues to so something even near freezing, but what or how, and how the health state of the yeast affects the lagering process, I can't seem to find enough information. I'm really surprised that there is not more information about this.
  13. TheBeerery

    TheBeerery Initiate (82) May 2, 2016 Minnesota

    Curveball. If you pitch proper amounts of healthy active yeasts, the yeast clean up the diacetyl while fermenting.

    Also D-rests cause the beer to off gas more residual carbonation and sulfur compounds. To which you have to replace the perfectly pure co2 with bottled unpure co2, and lose the antioxidant effects of the sulfur.

    Thus, D-rests will cause beer to stall faster than non D-rest beer.
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  14. frozyn

    frozyn Zealot (565) May 16, 2015 New York
    Premium Trader

    Trying to remember one of your posts from a while ago -- your pitch rate is around 2.5 mil and you lager for a couple weeks at 31?
  15. MorningDew72

    MorningDew72 Initiate (44) Aug 15, 2014 Washington

    Many ways to go about it. I'm not an expert on this subject but here's an interesting read regarding the maturation of lagers.

    See the "Maturation of the Beer" section. Should answer some questions, at least a good reference point. Trial and error, see what works for you.
  16. JackHorzempa

    JackHorzempa Poo-Bah (3,637) Dec 15, 2005 Pennsylvania

    I can report that I have brewed using 10+ different lager yeast strains and they have all performed well in my homebrewery using the scheme I detailed above. Needless to say but YMMV.

  17. VikeMan

    VikeMan Meyvn (1,453) Jul 12, 2009 Pennsylvania

    I feel compelled to add... Chris White is definitely an expert at turning small quantities of yeast into large quantities of yeast, and at delivering it to customers in remarkably good shape. This does not make him an authority on brewing. I would be willing to wager that most of the longtime regulars on this board have brewed more batches of beer than he has. That's not to say that his opinions about brewing have no merit. But I would keep this in mind.

    OTOH, if you're referring specifically to material from the book "Yeast," J.Z. was co-author, and he definitely is (IMO) an authority on brewing. (Not an infallible one though - nobody is.)
    OldBrewer likes this.
  18. JackHorzempa

    JackHorzempa Poo-Bah (3,637) Dec 15, 2005 Pennsylvania

    Needless to say that Dr. Chris White is not the head brewer of the 20 barrel brewery at White Labs – San Diego but there is a lot of White Labs corporate experience as regards brewing beer (see quoted material below).

    While I attended the National Homebrewers Conference (HomebrewCon) in 2015 in San Diego I wanted to make a side trip to White Labs but other activities took priority. On a related note Jamil Zainasheff gave a presentation on the topic of Yeast at that NHC.

    White Labs San Diego

    White Labs San Diego serves as our global headquarters. The facility has full production yeast making capabilities, an analytical lab, packaging, shipping and receiving, administrative offices and educational training rooms. We have a 20-barrel brewhouse on-site that produces beers to be featured in our 32-tap Tasting Room. Stop by and experience how much yeast impacts the complexity and overall profile of beer!”


    OldBrewer likes this.
  19. TheBeerery

    TheBeerery Initiate (82) May 2, 2016 Minnesota

    2.5, and 28-30F for 2 weeks. Filtered brilliant quality beer.

    It should be noted that these are taken directly from Narziß die bierbrauerei (of which I have). These fermentations ASSUME CCV's (cylindro conical vessels) these are many stories tall, and have massive hydro-static pressures on the yeast inhibiting ester productions. So this really doesn't apply to homebrewers.

    If you want to see what he ahs to say for "small" brewers you need to look into the "Classic fermentation profiles" which are quite different than these.
    frozyn likes this.
  20. JackHorzempa

    JackHorzempa Poo-Bah (3,637) Dec 15, 2005 Pennsylvania

  21. OldBrewer

    OldBrewer Aspirant (245) Jan 13, 2016 Ontario (Canada)

    Thanks Jack - this really explains a lot of what happens during lagering. I guess it's good to have some yeast still left over while lagering. It still doesn't answer the question about Chris White's 40 F milestone, but hopefully I'll find it eventually.
  22. NeroFiddled

    NeroFiddled Poo-Bah (9,925) Jul 8, 2002 Pennsylvania

    I think the 40 F "milestone" is simply that beer is at its densest at that point.

    And as far as a diacetyl rest goes overall, I've never done one and never had any issues. I think that's because I've never really rushed a lager, although I used to routinely turn the Bohemian Blonde at Manayunk in 16 days - keep in mind, A-B produces Budweiser in 16 days so maybe that's actually a long time (?). I was recently at a small brewery in Germany though where they noted that they lagered their beer for 40 days. But forgetting "lagering" time, if you allow the fermentation to proceed steadily and fully you should probably be ready to go and the lagering just helps to smooth the beer that much more.
    #22 NeroFiddled, Apr 20, 2018
    Last edited: Apr 20, 2018
  23. OldBrewer

    OldBrewer Aspirant (245) Jan 13, 2016 Ontario (Canada)

    It would seem that, without the diacetyl rest, it would be even more important to control the temperature of the beer once fermentation is complete. I believe Chris White mentioned that at 40 F, the yeast doesn't flocculate completely until at least 2 weeks. Thus, if you are not doing a diacrtyl rest, would you lower the temperature after reaching FG a couple of degrees a day until you reach 40 F, leave it there for a couple of weeks, and then crash it down to near freezing?

    By the way, at what point do you rack the beer?
  24. OldBrewer

    OldBrewer Aspirant (245) Jan 13, 2016 Ontario (Canada)

  25. NeroFiddled

    NeroFiddled Poo-Bah (9,925) Jul 8, 2002 Pennsylvania

    Ah, yes, the answer is probably right there in that upon reaching FG I'd leave the beer where it was for a day (which is basically a clean-up rest in itself),and then drop it by 5F each day or two to 40F. From there I would take it to 32F, although with the beer at its densest at 40F that seems unnecessary, at least concerning filtration. However, even without filtration I've found that whatever yeast is transferred over will drop bright in the keg within a few days. Rack it when you feel it's tasting properly and clear enough; that can vary depending on a variety of things including the generation of yeast you're on.
    OldBrewer likes this.
  26. JackHorzempa

    JackHorzempa Poo-Bah (3,637) Dec 15, 2005 Pennsylvania

    I typically brew on a weekend basis. An example batch would be brew on a Saturday and then two weeks later I would transfer to my secondary vessel. The beer likely could be transferred sooner than that but a timeframe of 14 days 'works' for my hobby brewing schedule.

    The beers at the 14 day mark are not exactly at final gravity for every batch. I have noted that for some batches the specific gravity will drop another couple points over the lagering timeframe. Some batches will have the same specific gravity reading after 14 days of primary as at the completion of the lagering phase.

    I always taste test my hydrometer samples. I do this principally as a QA/QC procedures (e.g., check for infection off flavors, etc.). My hydrometer samples for my lager beers consistently taste better after completing lagering vs. the end of primary samples.

    OldBrewer likes this.
  27. JackHorzempa

    JackHorzempa Poo-Bah (3,637) Dec 15, 2005 Pennsylvania

    Jim, the production schedule for a beer like Budweiser is about a month total:

    “5. Primary Fermentation: The wort is cooled and clarified, and the yeast is added; for six days, the yeast ferments the wort to beer.

    6. Beechwood Aging: During lagering, the beer is krausened, naturally carbonated and aged on beechwood chips for 21 days to mature the flavor of the beer. Anheuser-Busch is the only major brewer in the world using beechwood aging.”


    Prep8611 likes this.
  28. Ten_SeventySix_Brewhouse

    Ten_SeventySix_Brewhouse Initiate (127) Jul 20, 2016 Arizona

    How long do you typically leave a lager in primary? For my recent festbier, I pitched at a rate of roughly 2.0, pitched the yeast around 50°, then fermented for a week at ambient 46-48° before raising 5° per 12 hours up to 68° for the remainder of a second week. After those two weeks, I've kegged and lagered my lagers in the past, but this time I think I detected diacetyl.

    Should I just leave it on the yeast longer (is 3-4 weeks in primary ridiculous)? Will it go away during lagering? Should I krausen the beer? Does it even make sense that I have diacetyl, assuming my process as described? I used WY2308.
  29. VikeMan

    VikeMan Meyvn (1,453) Jul 12, 2009 Pennsylvania

    The thing about diacetyl is that even when you think you don't have it (like when tasting before packaging), it can still be made. At the same time that the yeast are cleaning up diacetyl that was already made, any precursor left over can still be converted to diacetyl. If you've ever seen the notional (net) diacetyl time line curve (from White Labs I think) it can be misleading, because the natural interpretation would be to think that diacetyl is produced until it peaks and then is cleaned up until it's gone, which isn't how it works. The only way to really be sure that your beer is no longer at risk is to take a sample and do a diacetyl force test. Most people don't do this. I don't.

    I wouldn't count on lagering to clean up diacetyl. There are two things working against you...less yeast and cold temperatures. Maybe it would happen given enough time, but as I said, I wouldn't count on it.

    Do you happen to know where your gravity was when you started raising the temperature? I wonder if your initial fermentation was slow-ish, and the diacetyl rest simply finished attenuation, but didn't have enough time to finish processing all the diacetyl precursor and diacetyl to the end.
  30. TheBeerery

    TheBeerery Initiate (82) May 2, 2016 Minnesota

    My lagers are in the fermenter no longer than 5 days ( then 2 days to FG and spund). I pitch at 2.5-2.7ml, ferment at 45f(no ramp) and always use 2206 or 835. Zero diacetyl.
  31. Ten_SeventySix_Brewhouse

    Ten_SeventySix_Brewhouse Initiate (127) Jul 20, 2016 Arizona

    I think I tasted diacetyl in the 68° hydrometer sample, but after heating and cooling, it definitely got more pronounced.

    I figured as much, so I left it in primary and raised the temp from 68° to 72°. It has been an additional 2 days since my tasting, and I planned to check it again this weekend. It it possible it will have cleaned up after an additional week on the yeast, even though my FG seems to have been reached beforehand (I measured 1.008.), or do I need to actively do something to eliminate it (i.e., pitch an actively fermenting starter)?

    I imagine that it happened as you describe. I did not take a gravity reading before ramping the temperature up, and I did it over the course of 48+ hours. Apparently, I should have started it earlier, as @TheBeerery says he only primaries lagers 5 days, and that is at a low fermentation temperature of 45°. My fermentation was likely done long before I did my D-rest, especially in a 1.048 OG beer. I also seemed to have a short lag period for a cold pitched (from a cold-crashed, decanted starter) lager (less than 24 hours), so I assume I pitched enough yeast.
  32. VikeMan

    VikeMan Meyvn (1,453) Jul 12, 2009 Pennsylvania

    Maybe. Maybe not. @TheBeerery has a very dialed-in process and he pitches like a MoFo. I suspect what happened with your beer is that for whatever reason, the total time (initial fermentation plus D-rest) was not quite long enough, i.e. the whole overlapping parallel cycle of making diacetyl's precursor (acetolactate) and then cleaning it up didn't quite run its course. I've never heard of someone having a diacetyl issue from raising the temperature too soon, but not giving it enough total time (including the rest if performed) can be a problem.
  33. VikeMan

    VikeMan Meyvn (1,453) Jul 12, 2009 Pennsylvania

    It's quite possible to do a diacetyl rest after reaching FG. The two things are not directly linked. Personally, I wouldn't pitch more yeast at this point.
  34. TheBeerery

    TheBeerery Initiate (82) May 2, 2016 Minnesota

    If it does in fact have it ( microwave test), krausening will fix it nearly immediately.
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  35. JackHorzempa

    JackHorzempa Poo-Bah (3,637) Dec 15, 2005 Pennsylvania

    Hopefully the extra few days will ‘fix’ the diacetyl issue.

    @pweis909 in a past thread discussed his method:

    “Warm the beer. Make a small starter of neutral dry yeast. I have done this with notty, us 05, and even lager yeast 34/70. It really shouldn't matter. You probably could use t59 and it wouldn't matter. When the starter shows signs of active fermentation pitch into your keg or secondary. Forget about the beer for 2-4 weeks. Drink.”


  36. Ten_SeventySix_Brewhouse

    Ten_SeventySix_Brewhouse Initiate (127) Jul 20, 2016 Arizona

    If it's still an issue after microwaving a sample this weekend, I'll probably go the Krausening route. Given that the beer is still in primary, would it be best to transfer to a keg before pitching the active yeast, or should I leave it on the cake? How long after pitching should I expect cleanup to take (i.e., days or weeks)?
  37. JackHorzempa

    JackHorzempa Poo-Bah (3,637) Dec 15, 2005 Pennsylvania

    There are answers to your questions in post #35 above courtesy of @pweis909

    "When the starter shows signs of active fermentation pitch into your keg or secondary. Forget about the beer for 2-4 weeks. Drink.”

    BA pweis909 did this for three of his batches and the net result was joy!

  38. Ten_SeventySix_Brewhouse

    Ten_SeventySix_Brewhouse Initiate (127) Jul 20, 2016 Arizona

    Sure, he said that it should be good in 2-4 weeks, but didn't say that it wouldn't be cleaned up more quickly than that. I was hoping for a low-end estimate, rather than a "safe side" estimate. I suppose I'll just play it by ear, but certainly not give up on it for several more weeks either way.
  39. JohnnyChicago

    JohnnyChicago Crusader (793) Sep 3, 2010 Illinois

    FWIW, diacetyl seems to be very batch and scale dependent. It (after gravity) is one of the first things brewers find when they scale up (or down) to a new location.

    Why is this important? If someone details their personal process and assures that they never develop diacetyl, it doesn’t necessarily mean that you won’t.
    Learn your system, build your process.
  40. JackHorzempa

    JackHorzempa Poo-Bah (3,637) Dec 15, 2005 Pennsylvania

    Give it a shot.

    Every homebrewer has their own unique system and every batch is it's own unique 'experiment'. I could tell you that I had success krausening to 'fix' diacetyl over x days but that does not mean that this timeframe will 'work' for you in your circumstance here.