Positive infuence of a reductive winemaking on the quality of Lugana wines

Lugana is a traditional white wine from the Garda Lake region (Italy), produced from a native grape variety, Trebbiano di Lugana. The grape composition was studied over two vintages, revealing a peculiar content in hydroxycinnamates and glutathione (GSH). This drew the winemaker’s attention on the possibility to optimise the winemaking procedure to improve the final wine characteristics. An innovative winemaking procedure based on the preliminary cooling of the grape berries followed by the crushing in an inert environment was implemented and explored over two consecutive vintages, at winery scale. The effects of these procedures on catechins, hydroxycinnamic acids, GSH, free and bound thiols content were investigated. The grapes, as well as the juices and the wines produced with the different protocols were examined. Moreover the wines aged for 1, 2 and 3 months after bottling were analysed. Finally, the sensory evaluation of all the wines was carried out. Particularly interesting was the high level of GSH found in the Lugana grape, which can act as a natural antioxidant and can be preserved in must and wines, thus reducing the need of exogenous antioxidants. Moreover, it appeared clearly that the polyphenol concentrations (hydroxycinnamic acids and catechins) were strictly influenced from the winemaking and pressing conditions, which required a fine tuning of the pressing. Above-threshold levels of 3-mercaptohexan-1-ol (3-MH) and 3-mercaptohexyl acetate were found in the wines, and changed differently according to the winemaking procedure applied. Interestingly, also the evolution during the first three months varied in accordance with the adopted procedure. Organic synthesis of the cysteine and glutathione conjugates was carried out and juices and wines were submitted to LC-MS/MS analysis. These two molecules appeared to be strongly affected by the winemaking procedure, but did not show any significant change during the first 3 months of post-bottling aging. This latter evidence supports the theory, already proposed in the literature, of other synthetic pathways for the free thiols formation. When produced under reductive winemaking, this grape variety gave wines with an intense fruity character, reminiscent of Maracuja aroma, with descriptors like “tropical” and “grapefruit”. According to a panel of winemakers and wine experts, wines produced with the reductive winemaking were evaluated positively for assuring a better sensory evolution during the first aging months in respect of those obtained with conventional vinifications.