Maceration-pressing operations

Crushing—Maceration—Pressing Operations. Fundamental to making any type of wine is the conversion of sugar to ethyl alcohol by the enzymes present in living yeast cells according to the equation established by Gay-Lussac,... 

Nevertheless, the dissolvent effect of sulfiting, with respect to phenolic compounds, is obvious in the case of limited maceration. This operation is not recommended for crushed white grapes before must extraction by pressing. The sulfiting of grapes also has an impact on the color of rose wines. 

For the production of white wine, it is almost universally accepted that a relatively clear juice of 0.5-2.0 percent suspended solids is desired for fermentation. This is achieved by separating the juice from the skins, pulp, and seeds. Many of the small wineries use a horizontal basket press to receive their fresh must. These presses utilize either an inflatable bladder or a movable piston to press the crushed grapes. In many cases, the must is pumped directly to these presses from the crusher-stemmer. An exception to this method of operation in small wineries is the case where skin contact is desired. Several wineries will allow maceration for from four hours to twenty-four hours for V. vinifera cultivars Chardonnay and Gewiirztraimer. 

The important elements are a mechanical digester or macerator and a small press. The digester consists of a horizontal barrel fitted with rotating beater arms and operated by a small diesel engine. This breaks up the fruit flesh into a pulp. The oil is extracted from the pulp either in a curb press, in which a heavy metal plate is forced down on to the charge in a perforated or slotted cylindrical container by means of a screw thread turned manually or in a small hand operated hydraulic press. These two devices enable up to 90% of the oil content to be recovered. The nuts are separated manually from the press residue and processed separately. 

If press capacity permits, crushing and destemming shonld be avoided and the grapes should be hand-harvested and pressed immediately. These operations are only necessary when the grape undergoes skin maceration before pressing. 

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