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Withering is a practice traditionally used in various regions to produce sweet or dry wines. During withering there is an increase in sugar content but also a modification in volatile compound profiles. Controlling metabolic changes through the dehydration process to obtain wines with desired characteristics is therefore a challenging opportunity. The effects of two different withering technologies, post-harvest or on-vine with blocked sap vessel flow, on the volatile profile of young and aged Corvina red wines was investigated. The results showed that modulation of wine aroma due to the withering process is associated with fermentative metabolites, such as esters, higher alcohols, and acids, as well as grape-related compounds such as C6 alcohols, terpenes and norisoprenoids. Significant differences were also found by comparing the two withering techniques. Post-harvest in a traditional “fruttaio” warehouse wines showed higher content of ethyl acetate, ethyl butanoate, β-citronellol and 3-oxo-α-ionol, whereas post-harvest withering on-vine increased β-damascenone in wines. The type of withering technique has an influence on the evolution of some aroma compounds during the aging of wine, among them linalool, (E)-1-(2,3,6-trimethylphenyl)buta-1,3-diene (TPB), n-hexyl acetate, ethyl acetate, ethyl 3-methylbutanoate, 3-oxo-α-ionol and β-damascenone.

Terpenes are important contributors to wine aroma. Free and glycosidically bound terpenes are primarily formed in grapes. During fermentation, they undergo important transformation catalyzed by yeast, so that the terpene profile of grape is substantially different from that of the corresponding wine. The present paper assessed the ability of a Saccharomyces cerevisiae strain to transform 17 different terpenes. Biotransformation was performed by placing target compounds in incubation with resting cells. Volatile compounds produced were extracted by solid-phase extraction and analyzed by gas chromatography−mass spectrometry. Geranyl acetate, neryl acetate, citronellyl acetate, and menthyl acetate were formed from the corresponding terpene alcohols. β-Citronellol was the main product of geraniol transformation; geranial, an intermediate of this pathway, has also been detected. Limonene was hydroxylated by yeast to form carveol, trans-2,8-menthadien-1-ol, and cis-2,8-menthadien-1-ol. Moreover, yeast cells were found to be able to adsorb a significant portion of the terpenes present in the reaction batches, with the extent of this phenomenon being linked to terpene hydrophobicity.

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