EFFECT OF DIFFERENT TEMPERATURE AND WATER-LOSS DEHYDRATION CONDITIONS ON THE PATTERN OF FREE AND GLYCOSYLATED VOLATILE METABOLITES OF ITALIAN RED GRAPES

Marselan wines have an unusual high proportion of seed derived tannins from grapes having high proportions of skins, which are rich in tannins. But the causes behind this characteristic have not yet been identified. In vintage 2023 wines were made at experimental scale (9 kg by experimental unit) from Arinarnoa, Marselan and Tannat Vitis vinifera grape cultivars by traditional maceration, and by techniques aimed to increase the wine content in skin derived tannin: addition of extraction enzymes, addition at vatting of grape-skin enological tannins, or by extended maceration, known to increase the seed derived tannin contents of wines. Macerations were of 7 days, except in the extended macerations that were of 15 days.

In 2022, wine production was estimated at around 260 million hl. This high production rate implies to generate a large amount of by-products, which include grape pomace, grape stalks and wine lees. It is estimated that processing 100 tons of grapes leads to ~ 22 tons of by-products from which ~ 6 tons are lees [1]. Wine lees are a sludge-looking material mostly made of dead and living yeast cells, yeast debris and other particles that precipitate at the bottom of wine tanks after alcoholic fermentation. Unlike grape pomace or grape stalks, few strategies have been proposed for the recovery and valorisation of wine less [2].

In a context of climate change and excessive use of agrochemical products, sustainable approaches for environmental and human health such as the use of bio stimulants in viticulture represent a potential option, against abiotic and biotic threats. Bio stimulants are organic compounds, microbes, or a combination of both, that stimulate plant’s vital processes, allowing high yields and good quality products. In vines, may trigger an innate immune response leading to the synthesis of secondary metabolites, key compounds for the organoleptic properties of grapes and wines.

The structural diversity is one of the most remarkable characteristics of proanthocyanidins (PA). Indeed, PA in wines may vary in the B-ring and C-ring substitutes, the C-ring stereochemistry, the degree of polymerization (DP) and the linkage between the monomers. Knowing in detail the structural characteristics of the PA of a wine can help us to understand and modulate several sensorial characteristics of the wine, such as color, antioxidant properties, flavor, and mouthfeel properties. In the last years was discovered and confirmed the presence of sulfonated monomeric and oligomeric flavan-3-ols in wine [1], as well as was pointed out their importance in wine quality [1,2].

Pinking is the emergence of pink tones in white wines exclusively produced from white grape varieties, known as pinking phenomena for many years. Pinking is essentially appeared when white wines are produced under reducing conditions [1,2,3]. Pinking usually occurs after bottling and storage of white wines, but its appearance has also been described after alcoholic fermentation or even as soon as the grape must is extracted [4]. Therefore, the purpose of this work was to investigate the existence of an-thocyanins in white wines made from different white grape varieties and grown locations and critically evaluate the most common method used for predicting pinking appearance in white wines: the Pinking Susceptibility Index (PSI).