Carbonic Anaerobiosis of Muscat Grapes. I. Changes in the Profiles of Free and Bound Volatiles

Abstract

Muscat de Frontignan grape berries were kept under carbonic anaerobiosis (CA) conditions at 32°C for nine days. Volatile components, both in their free and bound forms, were quantified in the liquid juice and the solid pomace obtained after pressing the berries. Compounds belonged to six groups: terpenols, alcohols, C₆ compounds, and to a lesser extent, carbonyls, esters, and nitrogenous compounds. The effect of CA on the distribution of these compounds was studied by comparing the four corresponding profiles with those of control samples. This work was carried out in duplicate over two years (1987 and 1988). Even if some differences in the extent of CA occurred, common features in the changes in the contents of the three main chemical classes were observed for both years of experimentation. Free and bound terpenols increased in the juice, so did free and bound alcohols. The ratios of concentration for nine days of CA over that for the control sample equalled 1.75 and 1.92 for the free and bound terpenols and 27.1 and 2.05 for the free and bound alcohols, respectively. CA might, therefore, enhance both the directly discernible aroma (free terpenols) and the aromatic potential (bound terpenols) of the grape, which could be of considerable technological interest. In addition, the free C₆ compounds, which may have unpleasant herbaceous notes, decreased in the juice fraction (ratio 0.55). Changes in the pomace were generally less than in the juice. The decrease in the content of bound terpenols (ratio 0.76) could be explained by their possible migration from the skin to the juice of the berries during CA.