Composition and Sensory Qualities of Wines Prepared from White Grapes by Fermentation with and without Grape Solids

¹ Department of Viticulture and Enology, University of California, Davis.

Wines were prepared from seven harvests representing six white grape varieties. The must of each harvest was divided into 3 or 5 equivalent lots. Lots were fermented dry at 16 C from juice clarified by settling, from turbid juice with double the normal amount of suspended solids, and from the entire destemmed, crushed grape mass inoculated with yeast and maintained in contact with the pomace for 24, 48, or 120 hours.

The expert panel of tasters judged wines prepared from clarified juice to be much higher in quality and desirable aroma than any of the other wines. Chemical analyses were essentially identical for the wines prepared from clarified juice or turbid juice, but the wines from turbid juice were much lower in quality and considered harsher (higher ratings for astringency and bitterness). The major quality difference between wines from these two treatments was due to the fresh, clean, delicate, fruity, characteristic odor called fermentation bouquet in wines from the clarified samples and its decrease or absence, plus off odors (particularly hydrogen sulfide) in wines from the turbid samples. The wines with increasing pomace contact exhibited increasing total phenol content coupled with increasing astringency rating. Pomace contact sufficient to give additional total phenol (as gallic acid) of about 100 mg/L from grape solids of seeded white grapes gave just recognizably increased astringency in white table wines. The wines with up to 5 days of pomace contact during fermentation at low temperature did not resemble red wines in flavor or odor, but remained similar to normal dry white wines, although with generally lower quality. Bitterness ratings did not parallel astringency or phenol content, and there appeared to be higher bitterness in intermediate levels of pomace contact and phenol content.

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