Vineyards - Calistoga California
Napa Valley, San Francisco North Bay, Ca. USA

Crushing and primary fermentation

Crushing is the process of removing the grapes from the rachis and breaking the skins of the grapes. In smaller-scale wine making, the harvested grapes are sometimes crushed by trampling them bare-footed. However, in larger wineries, a mechanical crusher/destemmer is used. Because the stems of the grapes have a relatively high tannin content, they are usually removed beforehand; otherwise they can give a vegetal aroma to the wine (due to extraction of 2-methoxy-3-isopropylpyrazine which has an aroma reminiscent of green bell peppers.) However the winemaker can decide to leave them in if the grapes themselves contain less tannin than desired. If increased skin extraction is desired, a winemaker might choose to crush the grapes after destemming. In these cases the grapes pass between two rollers which squeeze the grapes enough to separate the skin and pulp, but not so much as to cause excessive shearing or tearing of the skin tissues. In some cases, notably with "delicate" red varietals such as Pinot noir or Syrah, all or part of the grapes might be left uncrushed (called "whole berry") to encourage the retention of fruity aromas through partial carbonic maceration.