Influence of dehydration and maceration conditions on VOCs composition and olfactory profile of Moscato Bianco passito sweet wine

Abstract

Among the Vitis vinifera L. cv. Moscato, Moscato Bianco is the oldest and most cultivated one in Europe (1). According to the OIV Focus 2015, Italy is the country with the largest cultivated area of Moscato Bianco with about 12500 hectares (2), that is used to produce well-known wines (i.e., Moscato Passito in Piedmont, Moscato di Trani in Puglia, and Moscatello di Montalcino in Tuscany), mainly obtained from partially dehydrated grapes (1). Different dehydration techniques can strongly modify the chemical compounds of oenological interest, among which Volatile Organic Compounds (VOCs) (1) that are the main responsible for the varietal sensory character of the final wine.

The aims of the present research were to evaluate the effects of two different dehydration techniques (on vine; post-harvest) on the VOCs composition and odour profile of the corresponding Moscato sweet passito wines. Further, the introduction of a pre-fermentative cryomaceration step was also evaluated.
Moscato Bianco grapes, grown in Puglia (Italy), were used to obtain four wine samples: passito wines from grapes dehydrated on vine (oVD) and in post-harvest on plastic racks (pHD), vinified with skin maceration during the alcoholic fermentation (AF); the same two grapes were vinified with a pre-fermentative cryomaceration phase at 0°C for 4 days (oVD_pM and pHD_pM, respectively). VOCs and sensory profiles of the four wine samples were analysed by LL/GC-MS and descriptive sensory assessment (9 experienced and trained judges, 5 point numerical category scale). 

Results show that the different dehydration and maceration conditions significantly (ANOVA, p<0.05) influenced the volatile composition of the wines, allowing to obtain wines with different olfactory properties. Indeed, higher levels of some important terpenes (i.e., geranic acid, β-linalool, nerol, α-terpineol) as well as more intense floral odours were detected in oVD compared to pHD, showing intense honey and dehydrated fruits notes. This suggest that the on-vine dehydration is more preservative of varietal aromas, preventing the “sensory homologation” towards dehydrated notes. The introduction of the pre-fermentative cryomaceration step mostly affected VOCs related to the AF, namely esters, acids, and alcohols, but the floral character of oVD_pM was preserved. 

VOCs-odour and odour-odour correlations were tested by Person correlation (p<0.05): woody and honey descriptors were correlated (r=1.000) to each other, and to the same VOCs (ethyl vanillate, butyrolactone, furfural, 1-butanol, among others); the fruity character was positively correlated to esters, terpenes, and alcohols; dehydrated apricot and dried fig descriptors resulted strongly correlated (r>0.8) to acetoin.

References

1. Mencarelli & Tonutti (2013), Sweet, Reinforced and Fortified Wines: Grape Biochemistry, Technology and Vinification.
2. OIV (2015). Grapevine varieties’ area by country.