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Path: utzoo!watmath!clyde!floyd!harpo!seismo!ut-sally!mordor!wct
From: wct@mordor.UUCP
Newsgroups: net.wines
Subject: crystals in wine
Message-ID: <2100@mordor.UUCP>
Date: Wed, 28-Mar-84 11:46:20 EST
Article-I.D.: mordor.2100
Posted: Wed Mar 28 11:46:20 1984
Date-Received: Fri, 30-Mar-84 00:18:52 EST
Organization: S-1 Project, LLNL
Lines: 69

Well the first version of this was eaten by an errant Vax--sorry
its taken so long to reply.  

A more complete description of the processes producing crystals in wine.

The primary acid found in grapes is tartaric acid.  During fermentation
the tartaric acid is mixed with the other constituents of the grapes 
including compounds which include potassium.  This results in the 
following reaction:

Tartaric acid:
                 H--C(OH)--COOH
                 |
                 H--C(OH)--COOH
 
can combine with potassium to form
 
di potassium tartrate   H--C(OH)--COOK
                        |
                        H--C(OH)--COOK
 
or
potassium hydrogen tartrate
 
                         H--C(OH)--COOH
                         |
                         H--C(OH)--COOK
 
Now although the tartaric acid is soluble, di potassium tartrate is not,
and potassium hydrogen tartrate is only partially soluble--the result
is that most of these compounds precipitate out during the fermentation
producing a crystalline crust on the bottom of the barrel during latter
stages of fermentation.  The precipitation is temperature dependent,
with lower quantities remaining in the wine as the temperature is lowered.
This explains the absence of crystals in some wines and presence in others.
Modern winemaking in California, and this applies to both the jug and
vintage wines, usually employs a cool fermentation (say 50 to 65 deg f.) 
to produce a fresher, fruitier tasting wine.  Wines from Italy and many
other European regions are still made in a more traditional style with
fermentation temperatures above 70 deg.  Despite some aging at cooler 
temperatures, the end result is a wine which has not experienced the cool 
temperatures prevalent in American practices, so more of the tartrates
remain in the wine when it is bottled.  At this point it is stored in
cooler temperatures (45 to 55 deg) where the crystals form slowly with age.
 
I suspect that the total absence of crystals in conventional jug wines (and
I'll discount such abominations as Annie Green Springs ....as wine altogether)
is probably related to their storage at very cool temperatures while
awaiting bottling, waiting to be blended, etc.  In general, they are processed
much the same as other wines except for the extensive blending of high yield
grapes to obtain consistent results.  
 
Finally, do we have any other amateur winemakers out in netland?  A hobby I 
can heartily recommend to all wine drinkers.  
 
			Bill Thompson

To email correspondents:  our modem which was effectively down for three days
is back and email should work, but using 'reply' probably will not work.
The address header through UT-Sally will probably not work for email--try
a route through dual or decwrl as listed below.



-- 
	William C. Thompson III (S-1 Project, Lawrence Livermore National Laboratory)
        U.S. Mail: LLNL, S-1 Project, P.O. Box 5503, L-276, Livermore, Ca., 94550 
        Phone: (415) 422-0758
	MILNET: wct@s1-c or s1-a   UUCP: ...!decvax!decwrl!mordor!wct