Wine Production : Vine to Bottle - Vinum Vine

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10.2 Must preparation
The juice is drained from the press into settling tanks. If the must
is not cleared of solid matters, then off tastes can result. A simple
settling over a period of 12 to 24 hours, a process known in France
as débourbage, may take place. The must is then racked to another
tank for fermentation. Clarification can also be achieved by using
a centrifuge, which speeds up the process, or by filtration. Very fine
particles can also be removed by treating the must with bentonite.
This is a form of clay earth which acts as a flocculent, attracting and
binding fine particles which then settle out of suspension. If the
must is over clarified, fermentation may proceed slowly and the wine
may not ferment to completion. Yeast nutrients attach to solid matter
within the wine, making them accessible to yeasts. The removal of
solid matter can reduce the availability of nutrients, with detrimental
effects on yeast growth.
The must may then be passed through a heat exchanger to lower
the temperature. This not only prevents a premature onset of fermentation,
but also preserves freshness and flavours. The must is treated
with sulphur dioxide to prevent aerobic yeasts and spoilage bacteria
working. Selected cultured yeasts may then be added.
CHAPTER 10
10.3 Fermentation
The must is then pumped directly to the fermentation vats or barrels.
With careful winery design, this process can be achieved simply
by gravity, for pumping is by nature a harsh process. Selected cultured
yeasts may be introduced and are often used in white wine making.
White wine is usually fermented cooler than red wine, at around 10°
to 18 °C and over a longer period to preserve primary fruit flavours.
Each vat is under temperature control, usually with its own chilling
system. Cool fermentations are desirable for aromatic whites, with
less cool fermentations used when full-bodied wines are desired.
Some white wines are fermented in barrels to give particular characteristics
to the wines and a better integration of oak flavours. Barrels
also give a better supply of oxygen, required by the yeast in the early
stages of fermentation. The choice of new or used oak from particular
origins will have been made. It may be that different lots are fermented,