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Vinification, The Conversion Of Grape Juice Into Red Wine.

© Audra Ligumsky

When a grape is crushed to get the juice the combination of the yeast and sugar make alcohol and carbon dioxide. The carbon dioxide gas is released during the fermentation process.

Yeast comes from the skin of the grape. A grape on the vine has a waxy dull finish that yeast and bacteria in the air attach themselves to. The yeast on the grapes is both wine yeast and wild yeast. When the skins are crushed and the yeast comes in contact with the sugary juice the fermentation begins.

The color comes from the skin of the grape. Depending on how long the juice and the skins are left together is the difference between a rose-colored wine or deep ruby red. This fermentation process is closely controlled at commercial wineries.

Controlled fermentation is when the wild yeast and bacteria is killed off and only the wine yeast is left to ferment. Yeast is killed by adding specific amounts of sulphur dioxide to the grape juice. Yeast only works at a specific temperature so the juice for red wine is kept between 25 and 35' C. To achieve the right level of alcohol Chaptalisation is used. This is the addition of sugar for the yeast to feed on so the fermentation process keeps producing alcohol. It is up to the wine maker when the sugar is added. It may be added to the juice before or during fermentation. When the wine maker is happy with the color and level of tannins the wine is then drawn from the skins into a clean vat.

The remainder of the juice and skins are then pressed one more time to get the remainder of the juice. This juice is held as a Press Wine. It has high levels of tannins and is used to blend in part or hole to the wine achieving certain characteristics depending on the style of wine.

Fermentation ends after the yeast has eaten all the sugar. At this point the yeast dies and becomes sediment, called lees, and sits at the bottom of the vat.

To keep the wine from having a haze like substance in the appearance Bentonite is added to attract the haze particles and pull it down to the bottom of the vat and rests with the lees.

The wine is then drawn out and put in clean vessels before bottling. The next vessel the wine is stored in can be in a stainless steel tank or a wood barrel before bottling. It all depends on the flavors a winemaker is trying to achieve.

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