Effect of malolactic fermentation on the aroma properties of Tannat wine

Descriptive sensory profiles of Uruguayan Tannat wines following malolactic fermentation (MLF) with Oenococcus oeni were compared with control wines w here MLF was prevented. MLF led to a significant decrease (P < 0.05) in sec ondary descriptors such as 'berry fruit' and 'fresh vegetative', as well as a decrease in related tertiary descriptors such as 'blackcurrant', 'aprico t', 'cut green grass' and 'green pepper'. The main differences in the chemi cal composition of Tannat wine aromas following MLF were (1) an increase of the lactates (mainly ethyl lactate) over the sensory threshold; (2) a sign ificant decrease in ethyl esters and acetates, depending on the bacteria st rain utilised (the most significant change was found in hexyl acetate), and (3) a small increase of 4-vinylguaiacol and 4-vinylphenol with one of the MLF strains (this change was below the threshold of human perception). We a lso observed an increase of compounds related to alpha -ketoglutarate metab olism, namely: ethyl 4-hidroxibutanoate and gamma -butyrolactone. Differenc es in chemical composition due to MLF are discussed in relation to variatio n in sensory profiles.