Wine is simply an alcoholic grape juice or a more complicated definition - wine is a drink made from the fermented juice of freshly-picked grapes. Fermentation is a natural process caused by wild yeasts (outside of grape skin) or cultured yeasts (from laboratory). During the process, yeasts will convert sugar in grapes to alcohol or wine (main product), carbon dioxide and heat (by-products).

Generally, the more sugar the grapes have, the higher alcohol level the wine will be. However, you will only find wines (excluding fortified wines) with less than or equal to 15% alcohol. This is because yeasts will die when the wine alcohol level reaches 15% even though some sugar may still be left in the wine or the alcoholic juice.

Different yeasts may be more or less efficient at converting sugar to alcohol. Generally, it takes, roughly, about 16.5g/l of sugar to generate 1% alcohol. Interestingly, yeasts consumes less sugar for white wine to generate the same alcohol level of red wine.

Some wine makers will let the wild yeasts to “participate” the fermentation as they believe the yeasts may generate special aromas for the wine that is to be made. However, if a wine maker believes that the wild yeasts will produce some off-flavors to his wine, he may use sulphur dioxide to kill them and use cultivated yeasts alone for the fermentation. Different wines may use different cultivated yeasts to achieve certain wine styles. Generally, the main yeast used for alcoholic fermentation is Saccharomyces cerevisiae.

Wine types or wine styles can be broadly divided into three categories

Click types of wines to have more information. If you are interested to know how wine is made, click wine making process.