Usually, but not always made from white grapes (see Champagne), white wine production differs from red in that the juice is separated from the skins before fermentation. The tannins and phenols contained in the skins are considered undesirable for white wine as they impart bitterness and premature colouring.
On arrival at the winery the grape mass is de-stemmed and lightly crushed to release the juice. Sulphur Dioxide (SO2) is added to prevent oxidisation and to disinfect the wine. The mass is then pressed and the juice is run off into fermentation vessels, normally stainless steel, to preserve freshness and aroma, where it is allowed to settle. In general, the more gentle the pressing, the finer the wine. Temperature control is imperative throughout, as great heat is produced during fermentation, and oxygen must be excluded.
During fermentation the yeast will convert the grape sugars in the juice, now called 'must', into ethanol and release CO2 gas. Cultured yeast may be added to assist where necessary and acidity can be adjusted where permitted. The fermented must is then stabilised, filtered and fined for clarity and sent for analysis prior to bottling to ensure compliance with the laws of the region.
In some areas, notably the cooler regions, the alcoholic content of the wine may be increased by the addition of sugar to the must during fermentation. The process is known as Chaptalisation - named after Napoleon's Minister of the Interior, and also a chemist, who invented the process in 1801.
Some white wines, in particular Chardonnay, can benefit from several months in oak prior to bottling, the determining factors being the cost and the style sought by the winemaker.
