From: utzoo!decvax!harpo!npoiv!alice!rabbit!sif
Newsgroups: net.wines
Title: Fortified Wines
Article-I.D.: rabbit.1216
Posted: Sun Mar 13 02:04:37 1983
Received: Sun Mar 13 13:27:16 1983

Fortified wines are made by adding alcohol (usually in the form of brandy)
to the fermenting must.  This stops the fermentation and raises
the alcohol level.  If the fermentation was far from complete, the
resulting wine can be both sweet and alcoholic. Thus is port made.

It is true that many wine yeasts die in the 11-13% range, but there are
yeast cultures that are far more tolerant of ethanol. The grape and the
details of fermantation also control the degree of alcohol that the
yeasts can produce.
A number of California Chardonnays from 1981 are in the 15% range (and burn
acordingly).
Late Harvest Zinfandels routinely exceed 15% without fortification.
If memory serves, David Bruce made a Late Harvest Zinfandel in 1970 that
came in at 18.1%, allegedly without fortification! (The wine was wretched
but interesting).