Improved Red Wine Color Stability by the Prefermetation Addition of an Innovative Pomegranate Peel-Derived Tannin

Enological tannins are a class of coadjuvants employed in winemaking for their beneficial effects on must clarification, color, and mouthfeel sensations, while preventing oxidation. These polyphenol-rich extracts are regulated by the International Organization of Vine and Wine, which allows using tannins only from nutgalls, wood, and grape seeds and skins. However, growing attention to sustainability in the wine sector has prompted exploration of by-products from the food industry. Pomegranate peels, an important food industry by-product with ~ 0% discarded biomass of the fruit weight, can be valorized by extracting the tannin fraction for application in winemaking. Under the hypothesis that the unique chemical structure of pomegranate peel hydrolysable tannins, characterized by the gallagyl group, could be effective in preventing oxidation and stabilizing wine color, an innovative extraction method has been developed. Vinification of Sangiovese grapes was carried out, in which the addition of pomegranate peel tannin (PPT) was compared to the addition of nutgall tannin (NGT) and oak-derived tannin (ODT) and to a control (CON), with dosages adjusted according to the purity of the extracts. Polyphenol content, antioxidant activity, color indices, CIELab values, and sensory analysis were conducted at racking, after malolactic fermentation, and 6 mo after bottling. The results highlighted a significantly higher polyphenols content in PPT wines compared to the other treatments, resulting in an increased antioxidant activity comparable to NGT wines. The most notable effects were observed in color parameters: PPT wines had the statistically highest color intensity and presence of polymerized anthocyanins. Surprisingly, the addition of PPT led to significant reduction of wine bitterness. The study provided new practical insights on the advantages in using PPT in winemaking, strongly suggesting the possibility of extending the sources for recovery of effective enological tannins, while applying the principles of circular economy.