On Food and Cooking

After the Crush In the case of white wines,
the must is left in contact with the skins for a
few hours and removed with gentle pressure
before fermentation. It thus picks up little
tannic material or pigmentation. Rosé musts
and red wine musts are partly fermented in
contact with the red skins. The longer the
must is in contact with skin and seeds, and the
harder it is pressed, the deeper the color
(whether yellow or red) and the more
astringent the taste.
Before beginning the fermentation, the
winemaker usually adds two substances to the
must. One, sulfur dioxide, suppresses the
growth of undesirable wild yeasts and
bacteria, and prevents the oxidation of both
flavor and pigment molecules (the same
treatment is given to many dried fruits, and
for the same reason). Though this treatment
may sound antiseptically modern, it is
centuries old. One of the natural by-products
of fermentation that is increased by sulfuring