From varietal and terroir expression to off-odors: chemical background of wine aroma evolution during aging

Abstract

Expression of sensory attributes that reflect the varietal and geographical origin of wines (aka terroir) is central to perceived wine quality and reputation of wine producing regions. In wines from neutral varieties, this expression in the young wines is in part masked by the high content of fermentative aromas reflecting largely the technology of production. Conversely, after a period of aging, the concomitant decline of fermentative aromas such as esters and formation of novel aromas from different precursors can support the expression of terroir attributes. At the same time, during aging, the occurrence of chemical reactions involving specific precursors can also lead to the development of undesirable off-odors.

We have conducted a series of studies using both commercial and experimental wines, aimed at defining, for specific varietal models such as Lugana, Soave, Valpolicella, Amarone, Durello, i) the nature of the precursors supporting expression of both terroir features and off-odors; ii) the chemical factors modulating the extent of the underlying chemical reactions, and iii) key vinification operations suitable for their management.

Expression of terroir features during aging is linked, in these wines, to the presence of certain precursors in the grapes. Among these, glycosidic precursors of monoterpene alcohols determine monoterpene content of young and aged wines. However, other terpenoid precursors play a key role, in particular free forms of cyclic terpenes leading to the formation of the potent odorants 1,4- and 1,8-cineole. For both these compounds, a clear connection with grape geographical origin has been shown, allowing to define specific temperature and soil combinations most suitable for their occurrence, with pH also exerting an influence. Dimethyl sulfide is another compound associated with terroir expression, with grape nitrogen content playing a central role in its development during aging. Surprisingly, a very strong association was observed between vineyard geographical location and fermentation esters, supporting the notion that pure fermentation-derived aromas also contribute to expression of terroir features.

Concerning off-odor, accumulation of compounds with cooked vegetables off-odors such as methane thiol and dimethyl disulfide in white wines is triggered by light and temperature exposure. The chemical background determining the occurrence of these compounds is however strongly shaped by fermentation variables such as yeast strain and available nutrients. These results highlight once again the central role of fermentation in determining the future life of wine.

References

Luzzini, G., Slaghenaufi, D., & Ugliano, M. (2022). Approaches to the classification of wine aroma ageing potential. Applications to the case of terpenoids in Valpolicella red wines: This article is published in cooperation with Macrowine 2021, 23-30 June 2021. OENO One, 56(3), 231–242. https://doi.org/10.20870/oeno-one.2022.56.3.5393

Slaghenaufi, D., Luzzini, G., Avrini, G., Marconcini, S., Vela, E., & Ugliano, M. (2022). Occurrence, biogenesis and sensory impact of methyl salicylate in Lugana wines: This article is published in cooperation with Macrowine 2021, 23-30 June 2021. OENO One, 56(2), 91–100. https://doi.org/10.20870/oeno-one.2022.56.2.5389