Preparing for Fermentation
Crushing and Destemming
In this step, the process differs greatly in the production of white and red wines. The first step, whether done mechanically or by foot, is the crushing of the wine grapes. Most winemakers use a mechanical crusher or crusher-destemmer to release the sugar in the juice. This is the point at which stems would be removed, especially in white wine production. Stems can be astringent, a quality that is undesirable in a light white wine. In some full bodied white wine styles and many sparkling and sweet wines, whole bunches of grapes along with the stems are pressed.
The mixture of crushed, unfermented grapes is called must. At this stage, the grape must is either pressed or fermented depending on the type of grape. Red wines depend on skin contact for pigment and tannin, and are pressed after fermentation. White wines, on the other hand, become astringent when the juice is left in contact with the skins for too long. Another variable is the type of press. The harsher the grapes are pressed, the rougher the wine will be. Presses have been developed to squeeze the grapes as gently as possible in order to keep the seeds, or pips, from breaking and to keep from extracting astringency from the skins.
In red wine production, the solids are pressed after the juice has fermented and the wine has been run off. The liquid extracted in this process can be used in the final blend.
Settling and Clarification
Because clear juice ferments better than cloudy juice, it is usually clarified. Once the suspended particles have settled to the bottom of the tank, the clear juice is run off into the fermentation tank. In order to keep the juice from fermenting early, sulphur is often added and temperatures are kept low.