HOMEBREW Digest #5501 Wed 11 February 2009

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  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 Return to table of contents
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 Return to table of contents
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 Return to table of contents
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 Return to table of contents
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