Why, and when, was the term "dry" ( fr: Vin sec) selected to mean
lacking sweetness in "dry wine"?

Great question! Unfortunately, there isn't an easy answer to this.
Often, when tracking down word origins, we lose the scent and must
rely upon speculation. "Dry" in the sense of "lacking sweetness" has
been applied to wine for several centuries. The first use in print of
the English word "dry" in this sense comes a dictionary related to
winemaking. From the unabridged Oxford English Dictionary:

"Dry...
8. Of wines, etc.: free of sweetness and fruity flavour.
a 1700 B. E. Dict. Cant. Crew [A new dictionary of the terms ancient
and modern of the canting crew], Dry-wine, a little rough upon, but
very grateful to the Palate."

The Oxford English Dictionary is often a wonderful source of
etymological info, but in this case the OED says nothing about the
possible origin of this usage of "dry." There are various theories,
but no certainties. It is known that "sec," the French word for "dry,"
was applied to wines, and the English word "sack" (meaning sherry) may
have come from the French:

"Sack...  
 NOUN: 

Any of various light, dry, strong wines from Spain and the Canary
Islands, imported to England in the 16th and 17th centuries.

 ETYMOLOGY: 
From French (vin) sec, dry (wine), from Old French, from Latin siccus, dry"

Yahoo Dictionary: Definition of sack
http://education.yahoo.com/reference/dictionary/entry/sack_3

"Sec... 
  
ADJECTIVE: Dry. Used of wines, especially champagne.  
ETYMOLOGY: French, from Old French, from Latin siccus."  

The American Heritage Dictionary: Sec
http://www.bartleby.com/61/94/S0199400.html

The earliest known use in print of "vin sec" ("dry wine") occurred
around 1200, in "Jeu de Saint Nicolas," by Jean Bodel:

"from Trésor de la Langue Française informatisé 
1200 vin sec (JEAN BODEL, Jeu St Nicolas, éd. A. Henry, p. 100)."

Word Origins Discussion Forum: dry wine
http://p098.ezboard.com/fwordoriginsorgfrm1.showMessageRange?topicID=13419.topic&start=21&stop=40

Of course, tracing "dry" to the French "sec" doesn't answer the
question of why dryness, which usually means lack of moisture, should
be associated with lack of sweetness. The most plausible speculation
that I've come across is that "dryness" in this sense refers to the
mouth-feel of the wine, its tendency to desiccate or dry out the
palate.

"In medieval times (and pretty much up to the advent of modern
winemaking), wines were typically drunk young, since it was difficult
to keep them from spoiling. Any aging that was done would have been
done in wooden barrels, since the bottle- and cork-making techniques
of the time weren't good enough to permit long-term storage in the
bottle. (The ancient Romans and Greeks had airtight containers for
long-term storage and aging, but the art of making them was lost
during the dark ages.) So although it's possible to age the
astringency out of modern wines, in medieval times there would have
been a tradeoff between sweetness and astringency. As a general rule,
non-sweet wines would have been more astringent ('dry' in the mouth)
and sweet wines less so. From this, it's not surprising that 'sweet'
and 'dry' would have come to be regarded as opposites in wine, and
that non-sweet wines would continue to be called 'dry' even when
improved methods of winemaking led to the production of non-sweet
wines that weren't particularly astringent. This sort of evolution of
meaning by extension of an opposition into areas where one of the
terms is no longer literally applicable is common: consider 'sweet'
water vs. saltwater, or 'sweet' crude oil (or even coal) as a term
indicating low sulfur content. In short, 'dry' started off as a nearly
literal description of certain wines and changed its meaning somewhat
as wines changed."
 
Word Origins Discussion Forum: dry wine
http://p098.ezboard.com/fwordoriginsorgfrm1.showMessageRange?topicID=13419.topic&start=41&stop=60

"Astringency actually is a tactile sensation as opposed to a taste or
smell. The best way to describe astringency is a dry, puckery
sensation on the surfaces of the tongue and lining of the mouth. If
you have ever cracked open a pecan or a walnut and accidentally got a
piece of the hull in with the meat of the nut, you know what I mean by
dry and puckery. The same group of chemicals in both nuts and grapes
cause this effect, that is, the tannins."

Wine Lovers' Page: Wine Basics 102
http://www.wineloverspage.com/oxford/basics102.shtml 

"Dry 
Opposite of sweet; somewhat subjective in that tasters may perceive
sweetness to varying degrees. Usually a dry wine feels acidic on the
tongue and causes you to salivate, or your mouth puckers from the
astringency of the tannins."

F5: AltFood Glossary
http://www.f5wichita.com/food/index.php?pubdate=2005-02-03&story=2265

My Google search strategy:

Google Web Search: dry wine etymology
://www.google.com/search?hl=en&q=dry+wine+etymology

Google Web Search: dry sweet OR sweetness etymology
://www.google.com/search?hl=en&q=dry+sweet+OR+sweetness+etymology

I hope this is helpful. If anything is unclear or incomplete, please
request clarification; I'll gladly offer further assistance before you
rate my answer.

Best regards,
pinkfreud

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Request for Answer Clarification by cjohnsonmd-ga on 20 Mar 2006 12:36 PST

This is a nice summary of the information I was able to find with
more.  Much of this is covered on the string that I started on the
Wordorigins web site.  You didn't mention my guess that drying is
similar to water evaporating in the process of sugar being depleted
during fermentation.  "My thought was not that the sweetness
evaporates like water but that it gradually disappears. "To disappear;
vanish: Our fears at last evaporated"
It would have been apparent to early winemakers that the sweetness
gradually disappeared till dry, or without sweetness"
Nevertheless, I truly feel that no more objective data will be
available to further elucidate this etymology, and I applaud your
thorough summary.
Do we have any information on the context of the "vin sec" in the 1200
French reference?

---

Clarification of Answer by pinkfreud-ga on 20 Mar 2006 13:00 PST

I believe the French reference is to this excerpt from "Le Jeu de Saint-Nicolas":

"Le vin est nouvellement en perce, à pleins pots et à pleines tonnes,
vin discret, plein, courant comme écureuil en bois, sans nul goût de
pourri ni d?aigre; il court sur lie, sec et vif, clair comme larme de
pêcheur ; vin inséparable de la langue. Voyez comme il mange sa
mousse, comme on le voit sauter, étinceler et frire; tenez-le un peu
sur la langue et vous en sentirez le goût passer au coeur."

Beaujolais.com: LE BEAUJOLAIS NOUVEAU
http://www.beaujolais.com/pages/bpro/espacePresse/pdf/bn2004_fr_dp.pdf

An English translation:

"The wine barrels have just been broached, jars and tuns are brimming.
A discreet, full wine that runs like a squirrel in the woods, with
nary a rotten or sour flavor; it runs on the lees, dry and lively, as
clear as a sinner's tear; a wine inseparable from the tongue. See how
it eats its froth, see it leap, sparkle and gush; hold it a little on
your tongue and the flavor will go right to your heart."

Freelance News: Celebrating the 'Beaujolais Nouveau Fete Populaire'
http://www.freelancenews.com/news/contentview.asp?c=85118

I hope this helps. I have found no earlier use of "sec" in connection
with wine. I'm sorry that you were not fully satisfied by my answer.

~Pink

Thorough summary of available information on this subject.