Impact of Plasmopara viticola infection of Merlot and Cabernet Sauvignon grapes on wine composition and flavor

- New off-flavor reminiscent of herbaceous and cooked fruit nuances was evidenced in red wines.
- Incidence of Plasmopara viticola on theses aromas was demonstrated.
- Lactones, aldehydes and methoxypyrazine were associated with these flavors.
- In the winemaking process, a threshold of 5% infected berries was determined.

This work reports the identification of volatile compounds involved in the particular and atypical flavor detected in Vitis vinifera red Merlot and Cabernet Sauvignon wines made with grapes infected and wilted by brown rot (Plasmopara viticola). Must made from withered grapes had green aromas while red wines were marked by intense odor reminiscent of green, herbaceous notes but also figs and cooked fruit. Thanks to GC-O and GC-MS analysis, cooked fruit notes were identified as 3-methyl-2,4-nonanedione, γ-nonalactone and γ-decalactone, whereas herbaceous and green aromas were identified as (Z)-1,5-octadien-3-one and 3-isobutyl-2-methoxypyrazine. We show that the organoleptic impact of P. viticola is more pronounced in Merlot wines compared to Cabernet Sauvignon ones. The highest levels of 3-methyl-2,4-nonanedione (75.3 ng/L) were found in old Merlot wines made with 20% infected berries, suggesting the incidence of berry quality on the ability of a wine to age.