The botanical name for the common grapevine is Vitis vinifera and of the thousands of cultivars only around 30 grape varieties are commonly cultivated for wine production. Wine is made by the fermentation of grape juice obtained by crushing the grapes and then adding yeast to convert most of the natural sugars (glucose and fructose) in the grape juice into alcohol and carbon dioxide. The carbon dioxide is then released from the wine mixture into the air and the alcohol remains. After the primary fermentation, the liquid is transferred to vessels for the secondary fermentation or “ageing” process whereby the remaining sugars are slowly converted into alcohol and the wine becomes clear. Fining agents are used during winemaking to remove tannins, reduce astringency and remove microscopic particles that cloud the wines.
Wines are aged in either oak barrels or stainless-steel tanks before bottling. Sometimes oak chips are added to wine that is fermenting in stainless steel in order to enhance the taste. This process is mainly used in cheaper wines.
Red wines are produced by de-stemming and crushing the grapes into a tank and leaving the skins in contact with the juice throughout the fermentation. The presence of grape skin makes the wine red in colour. The most popular red varieties used in Australia include Cabernet Sauvignon, Merlot, Pinot Noir and Shiraz, while Cabernet Franc and Grenache are often used in blends.
White wines are mostly processed without de-stemming or crushing and are transferred from picking bins directly to the press. In contrast to the production of red wine, the juice is not left in contact with the grape skins while fermenting, resulting in a wine that varies in colour from golden yellow to a very pale yellow or light straw colour. The most common types of white wines include Chardonnay, Sauvignon Blanc, Riesling and Semillon.
Rosé-style wines are made by pressing ripe, red grapes but leaving the juice in contact with the skins for just a short time to extract the desired colour, usually a pale pink. The skins of the grapes are removed halfway through fermentation. Consequently, the flavour of rosés falls midway between whites and reds.
Sparkling wines contain carbon dioxide and come in red or white varieties. There are various methods by which those refreshing bubbles make it into your wine. Carbon dioxide may be injected into the wine, but this produces big bubbles that dissipate quickly in the glass. The Metodo Italiano, or the Charmat process, is one in which wine undergoes a secondary fermentation in bulk tanks and is bottled under pressure, producing smaller, longer-lasting bubbles. This is now used widely around the world to produce light, delicate, sparkling wines that are ready to drink. Then there’s the traditional method or méthode champenoise. With this method, the bubbles for more complex wines are produced by secondary fermentation in the bottle. This method is used for the production of Champagne and other quality sparkling wines and is more expensive than the Charmat process.