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HOMEBREW Digest #5501
HOMEBREW Digest #5501 Wed 11 February 2009
FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
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Contents:
Re: Yeast Performance / Aerobic propagation (Fred L Johnson)
crabtree and yeast (Fred Scheer)
Thanks for the response (robertzukosky)
Eis-Alt, anyone? ("Lance Harbison")
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Date: Wed, 11 Feb 2009 07:16:50 -0500
From: Fred L Johnson <FLJohnson52 at nc.rr.com>
Subject: Re: Yeast Performance / Aerobic propagation
Steve presented a good outline of what it would take to propagate
yeast in an aerobic respiratory phase. I especially appreciated
Steve's pointing out that more than the concentration glucose must be
considered--something that was never mentioned in any discussions or
readings I could find. (Steve: The yeast are not "aerobically
fermenting" unless they are producing ethanol, rather aerobic
respiration is the goal, but it was clear what you were describing.)
I played around with aerobic yeast propagation for a couple of years.
One way to do this is to begin the propagation in a small volume of
standard wort with aeration, allow the yeast to completely ferment
the sugars in this wort and then continuously pump in a concentrated
and fortified wort (or other synthetic medium) to this culture so
that the fermentable sugars in the wort are consumed at roughly the
same rate that they are added. One problem I had was that I didn't
have an easy way to determine exactly how fast to pump in the medium,
so I added it more slowly than I probably needed to. Consequently the
yeast were probably perpetually a little hungry, although I don't
know that this was detrimental. I also didn't have any
recommendations on how much of the other nutrients I needed to add.
Steve also did a good job describing this issue.
I got very good yeast growth, but with mixed results when I used
these yeast for fermenting my beer. I'm pretty sure most of my
problems were not that aerobically propagated yeast per se are poor
fermentors. Rather my problems came from my technique or likely my
wort composition, which was probably deficient in some essential
nutrient. (I believe yeast propagated in the respiratory phase are
used by many breweries and certainly in the yeast production plants,
but I don't have any figures or names of breweries using aerobic
propagation methods.)
I found that I got very good yeast growth and good beers using the
typical step-up method with constant aeration and stirring using
standard gravity or relatively high gravity worts added in steps
every several hours so that the ethanol production is minimized and
the gravity of the environment of the yeast was always pretty low.
Consequently, I have abandoned attempts to propagate yeast in a
strictly aerobic respiratory fashion quite some time ago.
Part of the reason I gave up on aerobic propagation was because I
couldn't find a yeast microbiologist interested enough to discuss the
subject with me. Experts in the brewing field just offered me the
equivalent of a, "Huh?", when I described what I was trying to do,
probably because the method is not commonly used or understood. If
there are others out there that really know about this propagation
method, I'd really like to hear from them.
Fred L Johnson
Apex, North Carolina, USA
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Date: Wed, 11 Feb 2009 13:37:51 +0000 (UTC)
From: Fred Scheer <fredscheer07 at comcast.net>
Subject: crabtree and yeast
Kai:
Crabtree effect describes the pathway whereby
yeast produces alcohol anaerobically
in the presence of Glucose in the medium.
Now, what we as brewers want, especially in
the lag phase is producing biomass via the
tricarboxylic acid cycle (Hough, briggs, Stevens,
Malting and brewing science, pp 54, 430 449-53, 579-80).
As the concentration of Glucose is increased,
Glycolysis will be accelerated. In this case,
the need for oxidative phosphorylation is reduced.
Also, the crabtree effect in yeast appears to be
correlated with the inhibition ofn terminal oxidation
and a restriction of the synthesis of the cytochrome system.
basically, in the presence of high concentrations
of Glucose normal mitochondrial structures tend to
disappear, especially the inner membranes.
The effect applies to both, Glucose and fructose.
DME vs. corn sugar
As you know, corn sugar is almost completely fermentable.
In bottle conditioning, I believe this is the easiest
way to produce the calculated amount of CO2 for your product.
DME (in fermentation, as starters!!!) needs a longer time in
the lag phase,but it has the needed yeast
nutrients, where corn sugar does not.
Also, DME is not completely fermentable.
Cheers,
Fred Scheer
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Date: Wed, 11 Feb 2009 08:00:49 -0700
From: robertzukosky <robertzukosky at comcast.net>
Subject: Thanks for the response
I want to thank all who responded to my questions on yeast performance.
The info has been very helpful.
bobz
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Date: Wed, 11 Feb 2009 22:07:56 -0500
From: "Lance Harbison" <harbison65 at verizon.net>
Subject: Eis-Alt, anyone?
At the suggestion of Jeff Renner I took advantage of the Pittsburgh climate
to lager an Altbier made in November on my back porch. During the first
deep freeze of January one full keg froze to the point where it pushed ice
up through the lid. There was nothing to do at that point so I let it be.
Well, in preparation for the last deep freeze (last week) I moved the keg
into my 32F fridge. I decided tonight to pour a glass which would contain
any yeast which may have settled since November. The poured glass was very
syrupy. I initially though that it was because of the yeast at the bottom
of the keg. I then opened the lid, looked inside, and was surprised to see
ice where it should have been beer.
I am now contemplating scooping out the ice and turning the beer into
Eis-Alt. Would this be considered experimental?
Lance Harbison
Pittsburgh
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End of HOMEBREW Digest #5501, 02/11/09
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