The majority of white wines are made from green or yellow-
skinned grapes, however if the juice is separated from the skins
gently and quickly, white wines can also be made from black-
skinned grapes. Upon entering the winery, the grapes are crushed
and destemmed, and the skins are then separated from the juice
before fermentation as the colours, flavour compounds, phenolics
and tannins found in the skins are usually not wanted in white
wines. The grape juice, or must, is now ready for fermentation.
The fermentation usually takes place in inert vats, such as
stainless steel, but can sometimes be done in oak barrels of
varying sizes. Barrel fermentation can add additional complexity
to a wine's aromas and flavours, with oaky and toasty aromas
being most apparent. To start the fermentation, yeast is added
to the wine, along with sulphur dioxide to prevent oxidation.
When the alcoholic fermentation is complete, the wine may
undergo a secondary fermentation - the malolactic fermentation -
to convert the harsh malic