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Old 04-07-2011, 12:27 PM   #11
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Ohhhhh-oh-oh it's magic, you know. Never believe it's not so.

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Old 04-07-2011, 12:28 PM   #12
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Originally Posted by ayoungrad View Post
I also enjoy homebrewing partially because of the science behind it. I was not satisfied with explanations for several things so I ponied up and bought Briggs' Brewing: Science and Practice. I have only read about 1/2 of it - it's over 800 pages. It is meant as a textbook for professional brewing but has a lot of relevance to homebrewing as well. It is definitely science-based and not experience-based. Unfortunately the science-based aspect means it is just as dry as most science texts. But it does have a few pages specific to the science of secondary fermentation (maturation).

Check it out. It could help in this discussion.
Thanks! Definitively checking it out!
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Old 04-07-2011, 12:30 PM   #13
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Unless you can propose another chemical pathway for things like diacetyl to be broken down,
Redox.

That was easy.
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Old 04-07-2011, 12:36 PM   #14
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In case someone wonders, my opinion (not proved in a brewing set up, just what makes sense to me biologically) was part of the other thread that went too off-topic and appropriately closed by the mod.

I did more research in this subject and this is the best I could find. Brewing is also science, and perhaps that is the main reason I like this hobby so much. For those who don't know, PNAS is a highly renowned journal in scientific research worldwide. It's one of my favorites. This particular article was NIH funded.

I encourage people interested in the matter to read it the article. You may find it overtly technical if you don't have a cell biology or molecular biology background, but you can skip the technical aspects about the results of their experiment and read the general well accepted knowledge about Saccharomyces cerevisiae, the common brewing yeast.

They do suggest that S. cerevisiae can carry on some degree of metabolic activity after starvation (i.e. sugar depletion), albeit minimal. Note that it is a common knowledge and also stated in the article that reentry in the cell cycle and peak of metabolic activity requires re-exposure of the yeast to its energy source, which is sugar.

So, perhaps the yeast play some role in the aging process after all but every reliable scientific resource I found to date confirms it's very minor at best.
I read the article. And by read I mean I read it like I read any such article - I read the abstract, the introduction and the discussion. So if I missed something, let me know...

But this article seems to be aimed at explaining why dormant yeast cells have a limited life span compared with those yeast cells that remain active. It is an article about the aging of yeast, not the aging of beer. The points you bring up have little to do with the thrust of the article.

But, in all sincerity, if you find an scientific article about the aging of beer, I would love to read it.
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Old 04-07-2011, 12:38 PM   #15
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04_srt: I'm a chemist and am really intrigued on the actual chemistry of brewing. Being a nerd, on my free time I read through the Journal of the Institution of Brewing.

http://www.scientificsocieties.org/jib/

This Journal will give you the scientific evidence you are looking for when it comes to the question, "How does this actually happen". I haven't seen an article directly pertaining to your question but I assume with a little work something will show up. I'll try and look through it as well to give you some hard scientific evidence.

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Old 04-07-2011, 12:39 PM   #16
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They do suggest that S. cerevisiae can carry on some degree of metabolic activity after starvation (i.e. sugar depletion), albeit minimal. Note that it is a common knowledge and also stated in the article that reentry in the cell cycle and peak of metabolic activity requires re-exposure of the yeast to its energy source, which is sugar.

So, perhaps the yeast play some role in the aging process after all but every reliable scientific resource I found to date confirms it's very minor at best.
You'll have to direct me to the part of the article that says anything about yeast activity levels in a sugar-poor environment, because I can't find a darn word. The article talks about transgenerational effects of stress, and in particular compares daughters of stressed cells to naturally aged cells. I might be missing something, but I don't see a connection to the role of yeast in processing metabolic intermediates once the majority of fermentation has completed.
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Old 04-07-2011, 12:44 PM   #17
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Here is a quote from Briggs re: diacetyl:

"Yeast cells will not assimilate exogenous acetohydroxy acids but will readily take up and reduce diacetyl and 2,3-pentanedione to acetoin and 2,3-pentanediol, which have no adverse flavours... This forms the basis of effective diacetyl removal from green beer..."

It goes on to say the the yeast need to be in a metabolically healthy state as you have mentioned. However, the book earlier mentions that the yeast can be in such a state with residual sugars in the fermented beer as well as by adding new sugar.

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Old 04-07-2011, 12:48 PM   #18
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Originally Posted by kcold0403 View Post
04_srt: I'm a chemist and am really intrigued on the actual chemistry of brewing. Being a nerd, on my free time I read through the Journal of the Institution of Brewing.

http://www.scientificsocieties.org/jib/

This Journal will give you the scientific evidence you are looking for when it comes to the question, "How does this actually happen". I haven't seen an article directly pertaining to your question but I assume with a little work something will show up. I'll try and look through it as well to give you some hard scientific evidence.
That is awesome. I wonder how long there will be free access?
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Old 04-07-2011, 12:58 PM   #19
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That is awesome. I wonder how long there will be free access?
Like most Journals, the newer publications aren't free. The ones that are a little older (maybe a year or so older) are free. I think the subscription is just a hard copy to get sent to your house and some additional perks but being right out of college, anything free is a good thing right now. Maybe when I get some extra money (that I don't actually spend on brewing), I'll subscribe just to give my thanks to the hours it kept me busy at work. lol
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Old 04-07-2011, 01:01 PM   #20
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I think I found the reference from Briggs on beer maturation through google. It has a little more info than Briggs but essentially says similar things. Here is (hopefully) the link:

http://books.google.com/books?id=UvuKGFnRgGoC&pg=PA348&lpg=PA348&dq=fermen tation+and+maturation+manual+of+good+practice&sour ce=bl&ots=dLHLKmdZN3&sig=-QWmO4bNSY70N_8lMJCff-HpjBU&hl=en&ei=0bOdTZTwBISXtweJosHfBA&sa=X&oi=book _result&ct=result&resnum=1&ved=0CBUQ6AEwAA#v=onepa ge&q=fermentation%20and%20maturation%20manual%20of %20good%20practice&f=false

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