Fining treatments are an important step in enology as they allow clarification and are reported to decrease the astringency of wines. Fining ability of a commercial gelatin and of two different molecular weight proteinaceous fractions derived from it (averaging 16,000 and 190,000 daltons, respectively) were studied in four wines with distinct composition of condensed tannins. The non-proanthocyanidin polyphenolic compounds did not precipitate with gelatins. The more polymerized and galloylated tannins were selectively precipitated, but the amount of epigallocatechin units was not significantly different from that of tannins of the corresponding wines. This observation suggests the important role of the number of accessible o-diphenolic and o-triphenolic rings in the precipitation process. The percentages of precipitated tannins were equal for the two fractions of gelatin studied (about 10%), while the tannins precipitated by the lower molecular weight gelatin were more polymerized than those precipitated by the higher molecular weight protein. The percentages of precipitation for the whole gelatin seem to be more dependent on the composition of wines, but in most cases the gelatin precipitated more tannins than the fractions (from 11 to 16%). The supernatants (treated wines) were significantly lower in tannins than the corresponding wines, suggesting that the reduction of astringency may be linked to the decrease of tannin concentration in fined wines.
- Fining treatment
- condensed tannins
- sensory evaluation
Acknowledgments: The authors thank Mrs. G. Guiraud from Suber Oenologie, France, for providing wines, Martin Vialatte for the gelatins, Martine Pradal for amino acid determinations, and Alain Razungles for help with sensory evaluation.
- Copyright 2001 by the American Society for Enology and Viticulture