Ask The Brewmasters

  • 1.  Yeast cell dispersion during fermentation of lager beers

    Posted 07-16-2024 12:21
    I recently saw a post regarding brewing myths that discussed the top fermenting vs bottom fermenting idea, and how it has become part of the general brewing public's lexicon. This was presented as simply wrongly attributing top cropping vs bottom cropping as terms to describe ale vs lager yeast behaviour post flocculation. Someone ( a professional brewing consultant) posted that, in fact because lager yeast ferment more slowly, and at lower temperatures, lager yeast tend to be found in higher concentrations at the bottom of the fermenter, rather than spread evenly throughout. Now I have certainly been guilty in the past of coming up with my own theories, and sharing them without researched based evidence. Which leads me to my question. Does anyone know of any research papers or text books that discuss the concentrations of yeast cells at different height levels in a lager fermentation. (primary fermentation not maturation where they are obviously mostly at the bottom).
    I've been referred to papers discussing the yeast distribution during multiple fills of a large cylindroconical fermenter. Also anecdotal information regarding sedimentation after primary fermentation and VDK rests are complete. The inference was that because lager fermentations are colder and slower the concentration of yeast in suspension is slightly higher at the bottom of the vessel than at the top, hence the term "bottom fermenting" I'd appeciate hearing any thoughts on the matter, and if such a research paper exists I'd love to take a look at it. 
    Thanks in advance


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    Stephen Parkes
    American Brewers Guild
    Middlebury VT
    (802) 352-4200
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  • 2.  RE: Yeast cell dispersion during fermentation of lager beers

    Posted 07-17-2024 14:02

    Hello Steve,

     

    Check out work by Chris Boulton. He has done quite a bit of research on large scale lager fermentations, - yeast distribution throughout the tank, how much yeast resides in the cone during fermentation (a lot), and the use of tank mixing technologies to improve fermentation consistency and tank cooling rates.

     

    Best regards,

     

    Tom

     

    Thomas H. Shellhammer, Ph.D.

    Nor'Wester Professor of Fermentation Science 
    Professor of Food Science


    Oregon State University
    Department of Food Science and Technology
    100 Wiegand Hall, Corvallis, OR 97331-6602
    Phone: 541.737.9308

     






  • 3.  RE: Yeast cell dispersion during fermentation of lager beers

    Posted 07-17-2024 19:34
    Thank you Tom,
    I did read his paper regarding the management of lager fermentations, along with another regarding VDK control.  That one did focus on multiple fills, high gravity worts, oxygenation late, and stirring/recirculating to control esters and diacetyl. There was a tremendous amount of useful information in that excellent paper, but it didn't exactly address my question. Is the traditional terminology of "bottom fermenting" accurate in the case of lager yeast in traditional fermentation systems? It's definitely "bottom cropping". On that we can all agree. And Ale yeast is "top cropping" as I've climbed enough ladders with a skimming pan in my time to know this for sure. And we also know that in a CCV all yeast are bottom cropping, and thermal currents due to cooling and vessel geometry, encourage excellent mixing, so yeast is dispersed evenly throughout the fermenter. 



    Original Message


  • 4.  RE: Yeast cell dispersion during fermentation of lager beers

    Posted 07-17-2024 19:35

    Hi Steve,

    I had the same thought as Tom. Here is a link to the specific paper I had in mind: TQ-50-2-0531-01.pdf (mbaa.com)

    Best,

    Christian Holbrook

    New Belgium - Bells Brewing Company



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    Christian Holbrook
    Brewmaster
    New Belgium Brewing Co
    Fort Collins CO
    (970) 221-0524
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    Original Message


  • 5.  RE: Yeast cell dispersion during fermentation of lager beers

    Posted 07-18-2024 15:23

    Thanks Christian. That was the first paper I found based on a couple of recommendations. The author starts by proposing that there is no way of exploring the distribution of yeast cells throughout the fermenter, since one can only sample over time intervals at a single (or a couple ) of fixed points. What I am hearing privately and anecdotally from a couple of brewers that while dropping fermenting beer to a maturation tank (1.0-2.0 P residual extract) there appears to be a higher concentration of yeast at the start of the transfer (ie the bottom of the fermenter)



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    Stephen Parkes
    American Brewers Guild
    Middlebury VT
    (802) 352-4200
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    Original Message


  • 6.  RE: Yeast cell dispersion during fermentation of lager beers

    Posted 07-19-2024 15:50

    Chris's work (as per Tom) is great stuff; but misses some points you appear to be searching for.

    Empirically, There are two different super-families of yeast; 

    the "very flocculant" and the more "normally flocculant" (as well as some modern "not-very-flocculant-at-all").

    'The "very flocculant" will be significantly on the bottom by ~60% of gravity drop; and you can (should) follow this by doing YIS every shift. These yeast strains drop so fast you can almost hear them hitting the bottom of the tank :). Some brewers actually move the beers off the yeast right after this point; so as to collect the yeast when it is in best condition; and allow the remainder to slowly complete fermentation (harder to do in verticals; so some move the beer out of shallow horizontal tanks (for early fermentation) into verticals (for late fermentation) just before reaching this flocculation stage to allow yeast collection from vertical and thus support their process methods).

    The "normally flocculant" yeast varieties will only relatively slowly drop out; and typically need some "push" from colder temperatures during fermenter cooldown to encourage more flocculation and thus clarification.

    Following your YIS provides you with better knowledge and appreciation of your specific yeast.

    Cheers, Keith



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    Keith Armstrong
    Retired
    Edmonton AB
    (780) 504-4245
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    Original Message


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