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Old 10-30-2012, 08:29 PM   #1
coryforsenate
 
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Has anybody tried this before? In theory, adding valine should feedback inhibit both the transcription of the operon for the branched chain amino acid genes as well as some of the biosynthetic proteins. This would reduce the yeast's need for valine which would reduce acetolactate production, which is the oxidative precursor to diacetyl.

I've had great success adding ergosterol and oleic acid to my wort while not oxygenating, so I think I'll try this out for my next lager.

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Old 10-30-2012, 08:33 PM   #2
ajdelange
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In theory that should work and would make an interesting experiment but as properly managed fermentation/lagering does not present a diacetyl problem I guess the question is, other than for the sake of science, why bother?

 
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Old 12-13-2013, 03:35 PM   #3
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coryforsenate, did you ever try adding valine?

 
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Old 12-13-2013, 04:37 PM   #4
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I added all 3 branched chain amino acids and pantothenate. All of those things are further down the pathway of the enzyme which produces acetolactate, so by adding all 4 things, you would in theory drastically reduce the production of acetolactate synthase enzyme and thus acetolactate.

Nothing I've submitted to competition has ever gotten a diacetyl mark on it, but whether that's due in part to my adding those compounds, I don't know. It's a fun and really cheap experiment though.
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Old 12-13-2013, 09:28 PM   #5
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Adding valine to the wort will reduce alpha-acetolactate (and consequently diacetyl) production during fermentation. Interestingly though, the absolute wort valine concentration doesn't seem to be that important, rather the ratio of valine to other (especially branched-chain) amino acids seems to be more influential on alpha-acetolactate formation (assuming the amino acids concentrations are sufficient for growth).

http://link.springer.com/article/10....253-013-4955-1

 
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Old 12-13-2013, 09:42 PM   #6
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Valine is a negative feedback inhibitor for acetolactate synthase.
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Old 12-13-2013, 10:09 PM   #7
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Yes, but for any wort valine to inhibit the AHAS enzyme, it first needs to be transported into the cell and mitochondria. The yeast cell has no specific valine transporters (rather valine is transported into the cell by a range of amino acid transporters; e.g. bap2p, bap3p, tat1p and gap1p), and hence the valine uptake rate will depend on the availability of other amino acids in the wort.

 
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Old 12-14-2013, 12:05 AM   #8
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Thanks coryforsenate, but it's not an experiment without a control group.

 
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Old 12-14-2013, 03:50 AM   #9
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So, where are you getting the Valine, and how much does it cost? Just looking at the abstract of that article, it says you need 100-300 mg/L, so that's around 2-6 g per 5 gallon batch (seems like a lot to me). This part is also a bother:

Quote:
Amino acid addition had a minor effect on higher alcohol and ester composition, suggesting that high levels of supplementation could affect the flavour profile of the beer.
I guess if the flavor impact is minor, it's not a big deal, but if a rest will get rid of the diacetyl, then it would be better to just pass on the Valine.

 
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Old 12-14-2013, 04:27 AM   #10
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It seems the 'modern' way to control diacetyl is via acetolactate dehydrogenase. There were at least 2 outfits hawking it at the MBAA conference in Austin last month.

 
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