Impact of spontaneous versus inoculated fermentation on the colour and phenolic profile of Nebbiolo wines from 32 vineyards

Red wine production relies on the alcoholic fermentation of grape must, conducted either through the inoculation of selected yeast cultures, or spontaneously with a complex microbial ecosystem comprising indigenous Saccharomyces and non-Saccharomyces strains. Crucially, the combined effect of maceration and yeast activity impacts the extraction of phenolic compounds, including anthocyanins, and the formation of derived stable polymeric pigments [1]. This behaviour is particularly important for monovarietal, like Nebbiolo wines, characterized by a low colour intensity. The study aimed to assess the potential impact of spontaneous fermentation on the general parameters, colour traits, and detailed anthocyanin and pigment composition by LC-MS/MS for the wines obtained from Vitis vinifera L. cv. Nebbiolo grapes (vintage 2024) from 32 vineyards. A multi-zone and vineyard approach was designed to minimize the confounding effects of regional variability. Each parcel was separately subjected to micro-scale winemaking, either with spontaneous fermentation or inoculation with Saccharomyces cerevisiae BRL97 strain, and the wines were analysed after 6 months. Partial Least Squares Discriminant Analysis (PLS-DA) was performed to generate Variable Importance in Projection (VIP) scores, identifying the key metabolic drivers distinguishing the fermentation modalities. On general parameters, glycerol was the most significantly affected, showing higher concentrations for spontaneous fermentation with a VIP score of 3.69. Specific monomeric anthocyanins were also found in higher quantities, including delphinidin (VIP 1.87) and cyanidin (VIP 1.76). Derived pigments were present in higher concentrations in spontaneously fermented wines. These included anthocyanin-flavanol adducts like malvidin-catechin (VIP 1.69), peonidin-catechin (VIP 1.35), peonidin-vinylcatechol (VIP 1.59), petunidin-vinylphenol (VIP 1.40), peonidin-vitisin B (VIP 1.28), and malvidin-vitisin A (VIP 1.19). These compounds potentially impacted the resulting colour intensity (VIP 1.56) and total anthocyanins (VIP 1.20). These results help to quantify the impact of spontaneous fermentation on derived pigments and their possible role in stabilizing colour.