Influence of withering on valpolicella docgs grapes volatile composition

Abstract

AIM: The blend of grapes used in the production of the four Valpolicella PDOs red wines, namely Valpolicella, Valpolicella Classico Superiore, Recioto della Valpolicella and Amarone della Valpolicella is quite unique, and includes two main varieties Corvina and Corvinone, and other minor varieties. To a very large extent all these grapes are only grown in the province of Verona. One of the main characteristics of Valpolicella is the use of grapes that are submitted to post-harvest withering. The aim of this study was therefore to evaluate the evolution of the free and glycosidically-bound volatile compounds in Corvina and Corvinone grapes under real production conditions.

METHODS: Corvina and Corvinone grapes from five different vineyards, at harvest and after 90 days of withering, were obtained from local winery during three consecutive vintages. Grape extracts were prepared with 800 grams of hand-crushed destemmed berries to which 141 mL of ethanol, 400 µg of dimethyl dicarbonate and 80 mg of potassium metabisulphite were added. Bottles were closed with screw caps and kept at 22 ± 1 °C for 14 days, during which they were hand stirred two times per day without opening the caps. Free volatile compounds and glycosidic precursors have been analysed by means of SPE- and SPME-GC-MS methods.

RESULTS: Most free and bound volatile increased in concentration with withering, in agreement with the fact that this process involve a significant degree of water loss (typically around 30%). However, for some compounds a decrease was observed with withering, including free cis-3-hexen-1-ol, 3-hydroxy-β-damascone and methyl salicylate. In the case of terpenes, more complex withering varieties interactions were observed. While in Corvinone all free terpenes increased with withering, in Corvina different patterns were observed, since β-citronellol and other terpenes increased while geraniol, linalool and α-terpineol showed similar content after treatment. Likewise, bound terpenes decreased in Corvina with withering, while in Corvinone they increased in two vintages out of three.

CONCLUSIONS:

Withering is a complex process in which, in addition to the simple water loss, a number of complex biochemical transformations occur inside the grape berry. These can affect volatile compounds of potential sensory relevance for Valpolicella wines in particular terpenes and norisoprenoids. Some variety-related differences in the evolution of certain aroma compounds during withering have been observed, with important consequences for the practical management of post-harvest withering.

ACKNOWLEDGMENTS:

Azienda Agricola f.lli Tedeschi is acknowledged for financial support