hist-brewing: Different Alcohols

Robert Lowe pngwen at acm.org
Fri Jan 11 14:33:18 PST 2002


There is a slight bit of truth to the "different alchohols" myth.  The
truth is that ethanol is only the most common alcohol produced by yeast
in fermination.  All yeast produce alcohols by breaking down peruvic
acid.  Peruvic acid is what a partially complete breakdown of glucose
produces.  The yeast cell breaks this molecule into Adeninetirphosphate in
order to fuel itself.

Now, depending on the sources of phosphoric acid, the yeast will produce
one of several hundred substances.  One type that can be caused by wild
yeast contamination is a modified ethanol molecule called
methyl-ethanol.  This is kind of modified ethanol is extremely
toxic.  Luckily it's also extremely toxic to the yeast that make it, and
therefore is generally not present in large quantities even if
contamination is really bad.  At any rate, it's possible to have yeast in
strains that will produce a modified ethanol substance.

Also, excessive amounts of any alcohol causes yeast cells to lyse (that
is, burst).  When ferminatation reaches its peak a good number of cells do
lyse.  The number depends on how quickly the toxicity level increases.  As
more cells lyse, it uses up a portion of alcohol and so the extreme toxic
reaction is typically avoided for alot of yeast who go on to become
dormant until priming.  The reason that this is important is because when
a yeast cell lyses, it always has a high build up of peruvic acid.  This
is one of the contributing factors in beer's flavor.  Human consumption of
peruvic acid will cause our cells to produce a bit of alcohol on their
own.  Thus, if there is a high concentration of this precursor to alcohol,
the impact of the alcohol becomes greater.

The type of fermentation used in beer making does produce more peruvic
acid than wine.  However it's extremely small.  Something in the order of
increasing the effective alcohol (consumed + produced) by about 1,000th of
one percent.

Anyway, I doubt they were thinking that when they wrote it.  I just
thought I'd share.  I'm sure I've made some mistakes somewhere in there,
but that is how I understand it to happen.  

-Bob

On Fri, 4 Jan 2002 PBLoomis at aol.com wrote:

>    In an article of beers, my local Friday supplement includes the 
> following statement:
>     "... don't confuse a 10 percent beer with a 10 percent wine -- the 
> alcohols in these drinks are different, and you'll find that a 10 percent 
> beer packs about the same punch as a martini."
>     There are two statements here (1) the alcohol in beer is different
> from the alcohol in wine, and (2) a 10 percent beer packs about the 
> same punch as a martini.  I don't believe either one of them.
>     Any of you knowledgeable people care to comment?
>     Scotti
>     Knowledge is never wasted, nor is the time to acquire it.
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