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From: c-hunt@tesla.UUCP (Charles Hunt)
Newsgroups: net.wines
Subject: Re: Yeast strains and boozology (and headaches)
Message-ID: <538@tesla.UUCP>
Date: Sat, 23-Feb-85 13:28:42 EST
Article-I.D.: tesla.538
Posted: Sat Feb 23 13:28:42 1985
Date-Received: Wed, 27-Feb-85 03:48:59 EST
References: <522@hou5g.UUCP> <1100@opus.UUCP>
Reply-To: c-hunt@tesla.UUCP (Charles Hunt)
Organization: Cornell University, Electrical Engineering Dept.
Lines: 23
Summary: 

Good point on yeasts.  However, no wine yeasts can tolerate above 17% alcohol
before they commit suicide.  Fact is, most American wine-makers intentionally
kill the natural yeasts in their musts before fermentation and then innoculate
the vats with yeast, almost always a strain very similar to what is used by
beer manufacturers.  These yeasts can't survive over 14.5%.  The only yeasts
that can live above that level are some very hardy wild strains (one of which
is used in Campagnia, Italy, and in high sugar years gets an intoxicating
16.8% before giving up the ghost).  Most dry wines were fermented to below
.5% residual sugar (below perceptable levels) and then racked to dispose
of trace yeasts with the lees, or, in the case of the "modern" producer,
centrifuged and filtered (which, arguably, gets other goodies as well).  The
sweet wines we enjoy (especially German) are cut short of finishing ferment-
ation by cooling the must to inactivate the yeasties, at which point they
are filtered or racked off, leaving the residual sugar.  In some rare, and
sometimes special, cases, the sugar is so high in the must that the yeasts
die before leaving the wine dry (eg some BIG Amador Zinfandels at 14.5%)
and the wine is "naturally" sweet.  In some even rarer cases (usually with
expensive rieslings) the must is innoculated with a gentle yeast which
cannot take over 11% or so, and the bugs die leaving residual sugar, even
though the must was not very high in sugar to start: but this trick is the
work of only a clever and talented winemaker.  Arguments as to the merits
of one technique over the other are endless and futile, in my opinion.
Cheers!  Drink a little: live long.                    =Charles Hunt=