Wine tannins: What place for grape seed?

Abstract

Phenolic compounds are among the most important quality factors of wines. They contribute to the organoleptic characteristics of wine such as colour, astringency, and bitterness. Although tannins found in wine can come from microbial and oak sources, the main sources of polyphenols are skin and seed from grapes. Yet, the link between grape seed phenolic content and wine composition, or even the link between seed maturity stage and wine composition are poorly studied. This work describes and explains the seed tannins kinetics release in wine, but also the impact of seed maturity stage on seed tannins extractability. 

The polyphenol content and composition of seeds at three different grape maturity stages were characterized (fifteen days before harvest, harvest and fifteen days after harvest). After that, an original approach of nanovinification was conducted. At each maturity stages three winemaking modalities have been produced in duplicate: (i) a control modality, (ii) a seed modality made of exclusively with seed and (iii) a skin modality made of exclusively with skin. The evolution of seed tannins release and tannins wine content has been followed during the winemaking, from alcoholic fermentation to maceration. 

Independently from the grape maturity stage, skin tannins are present at the first step of winemaking contrarily to seed tannins presence which is progressive all along the vinification. The results indicated that (+)-catechin is the less extractable free flavan-3-ols compared to (-)-epicatechin and (-)-epicatechin gallate. Furthermore the mean degree of polymerization of seed proanthocyanidins seems to be directly linked to their extractability, raising the question of the impact of tannins interaction and cellular location on tannins extractability.