Enhanced polyphenol extraction during Pinot Noir and Cabernet Sauvignon wine making

Abstract

The quality of red wine depends on the composition of polyphenols influencing wine color and taste. The question is, how much we must fear over extraction, especially of seed tannins, under cool climate conditions. The extraction of polyphenols from grape skins and grape seeds were investigated for the grape varieties Cabernet Sauvignon and Pinot noir. The experimental setup included seed removal, milling the seeds or the cap and returning them back, crushing the whole grapes prior fermentation, acidification of must as well as different techniques for the cap management. In 2018 as well as in 2019 the adaption of the enology in terms of maceration time, chaptalization and deacidification, depending on harvest time had been investigated. Photometric assays were used to determine total phenols, tannins and polymeric pigments. Anthocyanins and monomeric phenols were analyzed by HPLC-DAD/FD. Flavan-3-ol dimers and trimers as well as corresponding gallates were quantified by LC-QToF-MS. After bottling, descriptive sensory analysis was performed. The results showed that after seed removal, total phenolics and color intensity decreased. Crushing the seeds significantly increased total phenols, tannins, gallic acid and, for Pinot noir, also Large Polymeric Pigments. Additionally, a darker wine color was observed, indicating the importance of seed polyphenols for color stability. Acidification of must significantly contributed to wine color due to Small Polymeric Pigments, which were most likely formed by enhanced protonation of acetaldehyde, stimulating the formation of ethylidene-linked structures. Furthermore, catechin-catechin-gallate concentration was significantly increased due to acidification. This dimer may be released by the acid-catalyzed cleavage of interflavan bonds of higher molecular weight procyanidins. The sensory attributes color intensity, astringency, dry tannins and bitterness were the differentiating factors among the treatments. Crushing the seeds or the cap lead to the higher perception of phenol related in mouth modalities. The acidification of must leads to a significantly darker wine color while wines with seed removal lack in color and phenolic structure. Regarding time point of harvesting and technological maturity it seems the classical adjustment by means of sugar concentration is not able to simulate phenolic ripeness.