The Transfer of Polyphenolic Compounds from Grape Seeds into Wines

Abstract

A procedure was developed that appears to estimate the total extractable polyphenolic substances in grape seeds satisfactorily.

The relationship between alcohol content, temperature, time, and the extraction of tannin from grape seeds into model solutions was investigated. The percent of the tannin present which is extracted is expressed as a linear function of the logarithm of the elapsed time for several alcohol-temperature combinations in the range of 0-14% ethanol by volume and 52-86°F (11.2-30°C). In general, the tannin is extracted more completely in the same length of time by high temperatures and by higher alcohol content.

Calculations from these data indicate that grape seeds must contribute important amounts of tannin to red wines. Complete extraction of the tannin of the grape's seeds into the wine would give tannin contents of about 0.2-0.4%. Under the usual conditions of red wine fermentation it is estimated that an amount sufficient for about half of this concentration should be extracted from the seeds and, without other reactions and precipitations, should appear in the wine.