How Wine is Made
What is wine?
Wine is 80% biologically pure water, drawn from the soil by the vine itself. The other 20% is made up of: alcohol (obtained from the fermentation of sugar in the grape), a number of acids: tartaric, malic and citric (from the grape itself), lactic and acetic (from the alcoholic and malolactic fermentations), residual sugar (more or less, depending on whether the wine is dry or sweet), phenolic compounds (red pigment and tannins), volatile aromatic substances, and nutrients (amino-acids, proteins and vitamins).
How is wine made?
Grapes are considered to be ready for harvest when they develop the proper balance of sugar and acidity. After picking, they are put into vats to begin fermentation, the process that changes grape juice into wine. During fermentation, yeast (which is naturally-occuring on the grape but is sometimes also added to the juice) converts the natural sugar of the juice into two products: alcohol (wine) and carbon dioxide (a gas that escapes). Fermentation takes place under strict temperature control, so that it stops automatically when all the sugar has been converted into alcohol. However, if the juice has a particularly high sugar content, fermentation will stop when the alcoholic content of the wine reaches about 14%. In this case, the remaining, or residual, sugar will create a wine that is naturally sweet.
After fermentation, the new wine is put either into wooden barrels or into tanks for ageing. As the wine ages, particles called "lees" settle to the bottom of the container. The wine is "fined" to remove any solids that might still be suspended, then "racked" (drawn off into clean containers), leaving the lees behind. Right before bottling, the wine is filtered, to make sure it is absolutely clear.