Skin Particle Size Affects the Phenolic Attributes of Pinot noir Wine: Proof of Concept

Modifying phenolic composition can improve the quality of Pinot noir wines and overcome common challenges associated with deficiencies in color, tannin, and aging potential. During fermentation, extraction of desirable components from the skin takes place primarily through the inner skin surface of the berry and from broken skin edges. Ostensibly, the extraction of phenolic compounds located in the skin may be enhanced by reducing the skin particle size. Theoretical analysis indicated that moderate fragmentation substantially decreased the surface area to perimeter ratio of grape skins. Three experiments showed that cutting grape skins into smaller fragments facilitated egress of color and tannin from the skin into the wine matrix. In each case, the treatment in which grapes were cut was compared with a crushed berry control made using conventional methods. Homogenization of berry tissues increased tannin concentration by 6-fold, stable pigment concentration by 45%, wine color density by 25%, and blue-purple coloration by 20% in wines at six months bottle age. Undifferentiated cutting of grapes increased tannin by 6.5-fold, stable pigment concentration by 70%, wine color density by 60%, and blue-purple coloration by 10%. A cutting technique that reduced grape skins to 6% of their original size without damaging the seeds produced wines that had 3-fold higher tannin concentration, 95% higher stable pigment concentration, 50% greater wine color density, and 20% increase in blue-purple coloration. The effects of reducing skin particle size on phenolic extraction were found to be much greater than those achieved using pectolytic enzymes. This innovative skin fragmentation technique has the potential to increase skin-derived red wine phenolics and is a viable alternative to maceration techniques currently used during winemaking.