Influence of grape maturity and prefermentative cluster treatment of the Grenache cultivar on wine composition and quality

摘要

This work studied how different grape maturity levels and cluster treatments affect the color and phenolic composition of Grenache wines. Specifically, five treatments were undertaken at a microvinification scale for three maturity levels : Control (destemmed and crushed grapes), Whole Berry, Whole Cluster, Crushed Cluster and Submerged Cap. The first three treatments were also reproduced with large-scale wine fermentation in oak barrels but only with well-ripened grapes. The results indicated that the total polyphenol index (TPI), anthocyanin and proanthocyanidin concentrations, as well as the mean degree of polymerization were higher in all the treatments when the grapes were riper. Submerged Cap generated maximum color and polyphenolic extraction at the three maturity levels. Whole Berry wines were the most similar to the controls. The presence of stems (Crushed Cluster and Whole Cluster treatments) produced wines with a significantly higher pH at all maturity levels and with lower color intensity when the grapes were less ripe. The presence of stems also significantly increased the TPI in almost all cases. Introduction The quality of red wines is highly determined by the composition of phenolic compounds. Some of their sensory attributes, such as color, body and astringency, are mainly associated with the composition of anthocyanins and proanthocyanidins (Gawel, 1998; Vidal et al., 2003). Anthocyanins are only present in grape skins of most grape cultivars, with the exception of teinturier varieties, whereas proanthocyanidins are present in skins, seeds, and stems (Ribéreau-Gayon et al., 2000). Seed proanthocyanidins are made up of (+)-catechin, (-)-epicatechin, and (-)-epicatechin-3-gallate (Prieur et al., 1994), whereas skin proanthocyanidins also contain (-)-epigallocatechin and a much lower concentration of (-)-epicatechin-3-gallate (Souquet et al., 1996). Consequently, skin proanthocyanidins include procyanidins and prodelphinidins, whereas seed proanthocyanidins only consist of procyanidins. Little is known about stem proanthocyanidins, but it is thought that they are made up of the four monomers: (+)-catechin, (-)-epicatechin, (-)-epicatechin-3-gallate, and (-)-epigallocatechin (Souquet et al., 2000; Del Llaudy et al., 2008). Skin proanthocyanidins have a higher mean degree of polymerization (mDP) than seed proanthocyanidins but the polymerization degree of stem proanthocyanidins is a subject of controversy (Souquet et al., 2000; Vivas et al., 2004; Del Llaudy et al., 2008). It has also been reported that molecular sizes, and especially the monomeric composition of proanthocyanidins, have a considerable influence on the perception of astringency. More specifically, a greater degree of polymerization and a higher percentage of galloylation cause a greater perception of astringency (Vidal et al., 2004).It is well known that the maturity of grapes strongly influences the phenolic composition of red wines (Del Llaudy et al., 2008; Gil et al., 2012). Unripe grapes have lower extractability of anthocyanins and skin proanthocyanidins, but higher extractability of seed proanthocyanidins (Peyrot des Gachons and Kennedy, 2003; Canals et al., 2005). For this reason, immature grapes may produce more astringent wines because their seeds can release a greater quantity of highly galloylated proanthocyanidins (Del Llaudy et al., 2008). It has also been shown that stems can release highly astringent and bitter proanthocyanidins. Moreover, the presence of stems causes significant color loss and contributes to a ‘stemmy flavor’ in the wine (Boulton et al., 1995; Hashizume and Samuta, 1997). For this reason, destemming grapes is a common procedure in red winemaking in order to avoid these negative attributes. Other arguments for removing stems are that they reduce the ethanol content and titratable acidity, increase pH and even take up valuable space in the tank (Sun and Spranger, 2005).On the contrary, some winemakers argue that stems may occasionally have positive effects (Peynaud, 1984; Sun and Spranger, 2005). They claim that retaining stems produces wines with a higher concentration of proanthocyanidins, which helps to stabilize color and improve mouthfeel. Moreover, the presence of stems makes the cap less compact, which favors color extraction. Traditionally, stems have been used in red winemaking in such traditional regions as Chateauneuf-du-Pape (C?tes du Rh?ne), because their presence increased the polyphenolic content of wines and, therefore, improved their aging ability. Moreover, some winemakers in the Médoc region (Bordeaux) used to include a proportion of stems when grey rot was present, with the aim of inhibiting laccase and protecting wine color. Stems have occasionally been partially or fully used for low-tannin varieties such as Pinot Noir in traditional regions (Peynaud, 1981; Blouin, 2000). Nowadays, winemaking using the whole cluster is especially common in biodynamicatural wine production,