The Role of Pressing in Wine Production
In red wine production, pressing usually occurs during or after alcoholic fermentation to allow skin contact with the must. Although there are exceptions, white grapes and grapes used for sparkling wines are usually pressed right when they arrive at the winery to avoid skin contact.
Vertical basket pressing is commonly used for high quality red wine. The very smallest can press about 10 pounds of grapes at a time; the largest can handle several tons at a time. Smaller vertical basket presses are essentially large screws that are manually turned to exert pressure on the grapes. Larger ones use hydraulic motors to press the grapes.
Pneumatic pressing is usually used for white varietals. This type of press applies gentle, steady pressure to the grapes. A rubber piece is slowly inflated with air and the pressing begins.
Because destemming and crushing grapes inevitably macerates the must for some period of time, many winemakers forgo this step in high quality white wine production. Instead, they use a technique called whole cluster pressing. Pneumatic presses are usually used for this process.
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