How
Wine is made
Fermentation is the natural
process that turns grape juice into wine. Quite simply
fermentation is the chemical change of sugar into alcohol
and carbon dioxide gas brought about by yeast (which
you find on the skins of grapes). Under normal conditions
the yeast will continue to work until all the sugar
is used up or until the alcohol content reaches 15%
and the yeast are immobilised, it is however rare for
the sugar content of grapes to be this high. Without
interference therefore, almost all wine would be dry.
To produce sweet wines it is necessary for either the
alcohol content to be artificially raised, the yeast
to be immobilised by the addition of sulphur or removed
by filtration.
White Wine
Either white or red grapes
can be used to make white wine as the skins
are separated from the juice immediately and
the wine is fermented without them present.
The wine is left to ferment in a vat for differing
times depending on the type of wine being produced.
For sweet wine the fermentation process is stopped
while some sugar remains, whereas dry white
wine is allowed to fully ferment in the vat.
Sparking white wines are bottled before fermentation
is complete and continue to ferment in the bottle
where the wine becomes saturated with carbon
dioxide, which is released on opening in the
form of bubbles.
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Red Wine
Red wine is made solely from
red grapes that are crushed and fed into a
vat where they ferment along with their skins.
Fermentation occurs until all the sugar is
gone then the wine is run off (‘free-run’).
For a light, quick maturing wine the liquid
may be run off a few days before fermentation
is complete and allowed to finish in the barrels.
Passing the liquid and skins through a mesh
to produce a dark, harsh tannic wine produces
Vin de Presse. This can be mixed with free-run
to increase tannin and colour but this is
not common practice.
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Rosé
Again red grapes are fed through
a crusher and the liquid is allowed to ferment
with the skins for a minimal mount of time to
give the wine a pale pink colour. The liquid
is then run-off into another vat where normally
fermentation is completed, resulting in a completely
dry wine.
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