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	FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
		Digest Janitor: pbabcock at hbd.org


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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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