FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
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Contents:
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
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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
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End of HOMEBREW Digest #5848, 06/19/11
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