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Diacetyl Rest and Lagering

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

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  1. OldBrewer

    OldBrewer Maven (1,373) Jan 13, 2016 Canada (ON)

    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).
     
    #1 OldBrewer, Apr 19, 2018
  2. Brewday

    Brewday Zealot (721) 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.
     
    #2 Brewday, Apr 19, 2018
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  3. VikeMan

    VikeMan Grand Pooh-Bah (3,055) Jul 12, 2009 Pennsylvania
    Pooh-Bah

    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.
     
    #3 VikeMan, Apr 19, 2018
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  4. OldBrewer

    OldBrewer Maven (1,373) Jan 13, 2016 Canada (ON)

    That makes more sense than how it is explained in the book. At what point do you rack it off the yeast?
     
    #4 OldBrewer, Apr 19, 2018
  5. VikeMan

    VikeMan Grand Pooh-Bah (3,055) Jul 12, 2009 Pennsylvania
    Pooh-Bah

    I normally transfer to secondary (a corny keg) as soon as the D-Rest is finished.
     
    #5 VikeMan, Apr 19, 2018
  6. OldBrewer

    OldBrewer Maven (1,373) Jan 13, 2016 Canada (ON)

    Wouldn't you get more precipitants/flocculation by first lowering it down to about 50 F before transferring?
     
    #6 OldBrewer, Apr 19, 2018
  7. JackHorzempa

    JackHorzempa Grand Pooh-Bah (3,363) Dec 15, 2005 Pennsylvania
    Society Pooh-Bah

    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.”

    Cheers!

    https://byo.com/article/the-lowdown-on-lagering-advanced-brewing/
     
    #7 JackHorzempa, Apr 19, 2018
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  8. VikeMan

    VikeMan Grand Pooh-Bah (3,055) Jul 12, 2009 Pennsylvania
    Pooh-Bah

    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.
     
    #8 VikeMan, Apr 19, 2018
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  9. OldBrewer

    OldBrewer Maven (1,373) Jan 13, 2016 Canada (ON)

    Very good point! I'm sold :-)
     
    #9 OldBrewer, Apr 19, 2018
  10. OldBrewer

    OldBrewer Maven (1,373) Jan 13, 2016 Canada (ON)

    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".
     
    #10 OldBrewer, Apr 19, 2018
  11. JackHorzempa

    JackHorzempa Grand Pooh-Bah (3,363) Dec 15, 2005 Pennsylvania
    Society Pooh-Bah

    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.

    Cheers!

    P.S. FWIW I have a Kolsch in my lagering chamber right now (at the three week mark at the moment).
     
    #11 JackHorzempa, Apr 19, 2018
  12. OldBrewer

    OldBrewer Maven (1,373) Jan 13, 2016 Canada (ON)

    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.
     
    #12 OldBrewer, Apr 19, 2018
  13. TheBeerery

    TheBeerery Initiate (0) 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.
     
    #13 TheBeerery, Apr 19, 2018
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  14. frozyn

    frozyn Maven (1,423) May 16, 2015 New York
    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?
     
    #14 frozyn, Apr 19, 2018
  15. MorningDew72

    MorningDew72 Devotee (380) Aug 15, 2014 North Carolina
    Trader

    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.
    http://braukaiser.com/wiki/index.php/Fermenting_Lagers
    [​IMG]
     
    #15 MorningDew72, Apr 19, 2018
  16. JackHorzempa

    JackHorzempa Grand Pooh-Bah (3,363) Dec 15, 2005 Pennsylvania
    Society Pooh-Bah

    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.

    Cheers!
     
    #16 JackHorzempa, Apr 19, 2018
  17. VikeMan

    VikeMan Grand Pooh-Bah (3,055) Jul 12, 2009 Pennsylvania
    Pooh-Bah

    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.)
     
    #17 VikeMan, Apr 19, 2018
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  18. JackHorzempa

    JackHorzempa Grand Pooh-Bah (3,363) Dec 15, 2005 Pennsylvania
    Society Pooh-Bah

    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!”

    https://whitelabs.com/locations/white-labs-san-diego

    Cheers!
     
    #18 JackHorzempa, Apr 19, 2018
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  19. TheBeerery

    TheBeerery Initiate (0) 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.
     
    #19 TheBeerery, Apr 19, 2018
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  20. JackHorzempa

    JackHorzempa Grand Pooh-Bah (3,363) Dec 15, 2005 Pennsylvania
    Society Pooh-Bah

    #20 JackHorzempa, Apr 20, 2018
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