After the grapes are sorted, they are ready to be de-stemmed and crushed. For many years, men and women did this manually by stomping the grapes with their feet. Nowadays, most winemakers perform this mechanically. Mechanical presses stomp or trod the grapes into what is called must. Must is simply freshly pressed grape juice that contains the skins, seeds, and solids. Mechanical pressing has brought tremendous sanitary gain as well as increased the longevity and quality of the wine.
For white wine, the winemaker will quickly crush and press the grapes in order to separate the juice from the skins, seeds, and solids. This is to prevent unwanted colour and tannins from leaching into the wine. Red wine, on the other hand, is left in contact with the skins to acquire flavour, colour, and additional tannins.
Fermentation
After crushing and pressing, fermentation comes into play. Must (or juice) can begin fermenting naturally within 6-12 hours when aided with wild yeasts in the air. However, many winemakers intervene and add commercially cultured yeast to ensure consistency and predict the end result.
Fermentation continues until all of the sugar is converted into alcohol and dry wine is produced. To create a sweet wine, winemakers will sometimes stop the process before all of the sugar is converted. Fermentation can take anywhere from 10 days to one month or more.
Clarification
Once fermentation is complete, clarification begins. Clarification is the process in which solids such as dead yeast cells, tannins, and proteins are removed. Wine is transferred or “racked” into a different vessel such as an oak barrel or a stainless steel tank. Wine can then be clarified through fining or filtration.
Fining occurs when substances are added to the wine to clarify it. For example, a winemaker might add a substance such as clay that the unwanted particles will adhere to. This will force them to the bottom of the tank. Filtration occurs by using a filter to capture the larger particles in the wine. The clarified wine is then racked into another vessel and prepared for bottling or future ageing.