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Vinification of white
wine
As already mentioned, the substances which give a wine its
colour are mainly in the skin of the grape; in order to make white wine the skins
must therefore be separated out before vinification. This means that it is possible
to obtain white wines from both white and dark-skinned grapes. Only the pulp is
actually used and almost all varieties (and especially the more 'noble' ones)
have white pulp, regardless of the colour of the skin.
Grapes are pressed
in presses which squash the berries softly, so as to obtain the cleanest
possible must (juice). The must is then
clarified by filtration or centrifuging.
The resulting liquid, with the addition of a dose of sulphur dioxide (as an antioxidant
and disinfectant) is transferred to the vessel in which alcoholic
fermentation takes place. This is only filled to four-fifths of its capacity
so that the gas which develops during fermentation can occupy the space left above
the must, protecting it from damage which could result from contact with oxygen.
Using special equipment the temperature of the must is brought to 18-20°C. White
wines are, it may be noted, often fermented at a much lower temperature than that
which is ideal for red wines; too much heat would cause the end product to lose
some of its subtlety. It is important to maintain this temperature, taking action
when the heat developed in fermentation reaches 35-37°C, the point at which the
process would stop and bacteria would gain the upper hand, irreparably damaging
the wine. It is, therefore, essential to ensure controlled fermentation by governing
the temperature of fermentation through systems for cooling the vessels in which
the process is occurring. When the yeasts
have used up all the sugars contained
in the must - between ten and twenty days for white wines - the fermentation is
complete.
Depending on the type of wine which the producer wants to make,
the wine is then moved into wooden barrels or, after proper cleaning by filtration,
centrifuging and racking, into stainless steel containers before it goes on to
be bottled. The low temperatures preserve the aromas and slow down ageing of the
wine. The most modern bottling plants
allow the wine to be transferred while controlling its temperature and, using
microfilters, to get rid of any micro-organisms remaining in the wine which could
cause undesirable fermentation in the bottle.
For the most long-lasting and
important white wines it is advisable to carry out malolactic fermentation, lowering
the overall acidity of the wine. This
is the 'traditional' type of fermentation which may, however, be supplemented
with other techniques, such as cryomaceration.
The skins, as we have seen, hold most of the colorants, but also many aromatic
substances. By cooling the must (and thereby hindering the start of fermentation)
and leaving it in contact with the skins for a few hours it is possible to extract
the aromatic substances without any colour 'pollution'.
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