Interpreting wine aroma: from aroma volatiles to the aromatic perception

Abstract

Wine contains so many odorants that all its olfaction-related perceptions are, inevitably, the result of the interaction between many odorants. This natural complexity makes that the study of wine aroma has to deal not only with the quantitative determination of a large group of odorants, but has also to understand the basic principles determining the interactions between odorants. The basic mechanisms of odour interactions are not well known and seem to be very complex, but taking as base classical studies did by psychophysicists in the last 50 years, some outcomes of flavour chemistry, and some basic elements of the theory of perception, it has been recently possible to propose a systematic classification of odour interactions into four different categories: competitive, cooperative, destructive and creative. 
Competitive interactions take place when two or more non-blending odours are simultaneously perceived. The perceived intensity of any of them decreases as the odour intensities of other of the components is increased. Cooperative interactions take place when many odorants are present at subthreshold levels and are particularly relevant when similar odorants are present at whatever odour intensities. In these last cases, these interactions lead to the formation of odour vectors, which are groups of odorants of similar aroma acting concertedly and translating to the final product a specific aroma feature.  Destructive interactions take place when one of the odours present in the mixture is able to deconfigure the odour perception of the others, bringing about a decrease in the odour intensity before the deconfiguring odour is perceived. Most wine off-odours belong into this category. Creative interactions are configurational processes and take place when a new odour emerges out of the mixture of odorants. In milder cases, the addition of one odorant boosts the intensity of the others present in the mixture.
With these elements at hand, it is possible to propose a systematic to understand the chemical bases of wine aroma perceptions. Overall, around 80 aroma molecules, seem to be able to explain the different positive aroma nuances of all wines. The major wine volatile components, all of them by-products of alcoholic fermentation, form “the wine aroma buffer”, which is a mixture with vinous aroma and a strong deconfigurational power induced by the destructive interactions elicited by ethanol, isoamyl and isobutyl alcohols and acetic acid. Then, wine odorants are further classified into 35 different aroma vectors, broadly classified into 10 different odour categories. Some creative interactions, leading to relevant wine odours, such as pineapple, strawberry candy, black fruits or raisins have been also identified and will be discussed.