HOMEBREW Digest #5848 Sun 19 June 2011

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  Re: Yeast mass vs. Yeast count (Fred L Johnson)
  Re: Yeast mass vs. Yeast count (Joe Walts)

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---------------------------------------------------------------------- Date: Sat, 18 Jun 2011 07:17:11 -0400 From: Fred L Johnson <FLJohnson52 at nc.rr.com> Subject: Re: Yeast mass vs. Yeast count -S, known to many of us as Steve, :-), responded to my post on yeast growth with lots of good points and questions. As Steve probably suspected, I don't have good answers to his questions because I didn't perform this little "study" with any real control. I just retrospectively tried to look at what I had recorded to attempt to make some sense of the variability I was seeing in my yeast propagation results. Steve asked: > Did you measure OG & SG then estimate a real > attenuation ? Or just use the OG ? Was the starter wort standardized > in some way or is it's attenuability & FAN variable ? The worts used in these studies were mostly worts left over from full batch brews, so there was no attempt to standardize the wort. I always store wort from each brew to use as starter medium. I did measure the attenuation of each brew, but not of the starter worts, and certainly knowing how much sugar was used in each wort would be a better way of getting at the issue. Still, the variability in attenuation probably can't account for much of the large variabilty I was seeing in cell counts. Steve commented: > At the end-point cells going dormant can accumulate a considerable mass of > trehalose, & glycogen as storage carbs. This adds considerable to yeast > (dried) mass. Unclear about the impact on volume. You may be catching > cells in various phases of carbo-loading, but your measured variation seems > too large for that. I do see much smaller variability in cell size within a culture (not quantified, just overall impression) of a strain and fairly consistent cell size within a strain at the end of my propagations. The Wyeast 3944 was remarkably smaller in size overall compared to most others I've used. The only thing that is consistent here is that all the cultures were well aerated throughout the culture and were examined after they had consumed when they had used up all the fermentable sugar. Steve asked: > Did lager strain data cluster differently than ale ? Are the various yeast > variety consistencies ? Probably hard to tell with 19 data points. Only six of the fermentations using three strains were lager strains, so there were not many data. I didn't see any clustering with these few data points. Steve commented: > ... a few percent of aerobic fermentation in your > stirred, aerated starter may be responsible for a considerable fraction of > yeast mass. We also have to consider growth limiting factors. After carbon > source and O2/sterol then nitrogen is at issue. Wort has sufficient > ammonia/amino acids for anaerobic fermentation but should fall far short > for aerobic fermentation. I really would like to know what would be close to ideal amounts of nutrient additions to an all grain wort for propagation purposes. I suspect Wyeast and White Labs could tell us, but it hasn't trickled down to us homebrewers. Steve asks: > So one useful question is "How little (mass or volume) of yeast meets the > minimal requirements for a good fermentation ?". and > Another question is "How can we produce more > and better yeast starters at a modest marginal cost ?". I'd love to see more posts on this. Fred L Johnson Apex, North Carolina, USA Return to table of contents
Date: Sat, 18 Jun 2011 08:55:19 -0500 From: Joe Walts <jwalts at gmail.com> Subject: Re: Yeast mass vs. Yeast count Fred, thanks for conducting such an interesting experiment. I just read Standards of Brewing by Charles Bamforth, and Charles mentions that brewers often pitch by weight for convenience but should base their weights on cell counts whenever possible. He doesn't get into specifics aside from noting that cells can be different sizes depending on conditions. I suppose that's one obstacle to an entirely mass-based pitching scheme: although different strains may always vary in size, there can be a lot of variation within the same strain depending on the health of the yeast and its surroundings. Another obstacle, as S points out, is a need to achieve a dry mass or weight, because yeast slurries contain a lot of beer - and the amount varies from pitch to pitch. I'm no biologist, but I suspect the impact of cell mass variance depends on how much it's attributed to the parts of cells that perform metabolic functions. For example, does a cell with twice the mass of another have twice the enzymes or just a lot more water and salts? I hope this topic generates a lot of discussion. Joe Return to table of contents
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