Crushing

Modern mechanized wine production crushes and removes the stems at the same time. A crusher-stemmer machine consists of a perforated cylinder containing paddles revolving at 600 to 1,200 revolutions per minute. The grapes are crushed and fall through the cylinder perforations. Most of the stems pass out of the end of the cylinder. A roller-crusher may also be used. Ancient methods of crushing with the feet or treading with shoes are rare, but still acceptable.

When red grapes are used to produce a white juice, as in the Champagne region of France, crushing is accomplished by pressing.

Red grapes are sometimes introduced whole into tanks, which are then closed. The resulting respiration in the fruit, consuming oxygen and producing carbon dioxide, kills the skin cells, which lose their semi-permeability, allowing easy color extraction. There is also some intracellular respiration of malic acid. This respiration process is slow and in warm regions may result in wines of low color and acidity and distinctive odor.