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Q: biology ( Answered,   1 Comment )
Question  
Subject: biology
Category: Science > Biology
Asked by: matchette-ga
List Price: $7.00
Posted: 15 Nov 2003 04:49 PST
Expires: 15 Dec 2003 04:49 PST
Question ID: 276079
why might winemakers try to minimizethe amount of air available to
yeast during fermintation
Answer  
Subject: Re: biology
Answered By: feilong-ga on 15 Nov 2003 11:38 PST
 
Hi Matchette,

Thanks again for another interesting question. The simple answer to
your question is to ensure proper fermentation and prevent spoiling
the wine. The explanation can be found below:

"When yeasts enter a new environment, they exist for a while in what
is known as a lag period. During this period, which can last from
minutes to hours, the yeasts basically test the environment to
determine whether or not it is suitable for colonization. If they
determine that it is, they end the lag period and begin reproducing.
Yeast can reproduce at an alarming rate in a favorable environment.
This rate, at least for a period, is typically one logarithmic unit
per two hours, meaning that 1 yeast cell can theoretically become 8 in
six hours, 64 in 12 hours, 512 in 18 hours, and 4096 in 24 hours.
Luckily, when their population density reaches about 150,000,000 per
milliliter of host liquid, they settle down and maintain a relatively
steady population. This continues, all other conditions remaining
constant, until they deplete all available oxygen, use up all
available nutrients, or the alcohol they produce becomes intolerably
concentrated. Most then die off, but if both OXYGEN and nutrients are
still available then BRETTANOMYCES, DEKKERA AND ZYGOSACCHAROMYCES
BAILII, if present, may now decide to end their lag period and begin
multiplying, ruining what would otherwise be an almost finished wine."

(Exerpted from The Winemaking Home Page by Jack B. Keller, Jr. - The
Miracle Of Yeast, Copyright  2003
http://winemaking.jackkeller.net/yeast.asp )

"A stuck fermentation is difficult to restart and dangerous because
once the yeast stop growing, the protective layer of carbon dioxide is
removed. The door is open for spoilage yeast and bacteria
(BRETTANOMYCES, LACTOBACILLUS AND ACETOBACTOR) to consume the
remaining sugar in turn producing vinegar, earthy, barnyard or
sauerkraut aromas."

(Exerpted from Enology International - Going Wild: Wild Yeast In
Winemaking by Jordan P. Ross, Copyright  2002
http://www.enologyinternational.com/yeast/wildyeast.html )

The air we breathe carries oxygen and other microbes that could ruin
the fermentation process in winemaking, which could result in
unfinished or bad wine. Even worse, one could end up making vinegar
instead of wine. By minimizing the amount of air present during
fermentation, the risk of spoilage is reduced, if not virtually
eliminated.


Additional references:

HowStuffWorks, Inc.
How Winemaking Works
http://people.howstuffworks.com/winemaking7.htm

You can find more references through the last link below.


Search strategy:

Keyword searches at HowStuffWorks.com

yeast winemaking - in Google Web search
://www.google.com/search?num=100&hl=en&lr=&ie=ISO-8859-1&newwindow=1&safe=off&c2coff=1&q=yeast+winemaking&btnG=Google+Search


I hope this helps you. Should you have any comments/questions, please
feel free to post your clarification before rating this and I'll
attend to you as soon as possible. Thanks for asking.

Best regards,
Feilong
Comments  
Subject: Re: biology
From: proteosome-ga on 27 Nov 2003 10:13 PST
 
Yeast only produce alcohol (ethanol) under anaerobic (no oxygen) conditions.

If oxygen is present than yeast, and humans, will use glucose to make
a lot of ATP (energy).  When oxygen is not present, this reaction
cannot proceed and a side reaction is used to make ATP that is not as
efficient and produces bad side effects (lactic acid in humans,
ethanol in yeast).

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