Influence of Different Pressing Systems on the Composition of Volatile Constituents in Unfermented Grape Musts and Wines

Abstract

The influence of processing conditions on the composition of aroma constituents in unfermented musts and wines was studied. Unfermented musts from grapes of the varieties Morio-Muskat and Müller-Thurgau, harvested in 1978 in Rheinpfalz, West Germany were produced by three methods: A) screw press; B) cylindrical Willmes press; and C) method of B plus a pressing-aid material. Three different fractions were obtained (free-run and two pressing fractions). Quantitative gas chromatography revealed that the amounts of varietally distinct aroma substances, terpene alcohols, and "terpene oxides" in the pressing fractions increased with pressure. The amounts were nearly the same for systems A and B, and 34-45% less for system C. Losses of varietal volatile substances were detected also in wines from musts of system C. Also studied were changes in fermentation by-products of wines produced from the must fractions processed by different methods. An increase of pressure during pressing resulted in increased formation of ethyl esters and acetates in the corresponding wines. The concentrations of these fermentation by-products were highest in wines made from pressing fractions of system C.