Specificities of red wines without sulfites: which role for acetaldehyde and diacetyl? A compositional and sensory approach.

Abstract

Sulfur dioxide is the most commonly used additive in oenology to protect wine from oxidation and microorganisms. Once added to wine SO2 is able to react with carbonyl compounds to form carbonyl bisulfites what affects their reactivity. All together these carbonyl bisulfites correspond to bound SO2. The affinity of each carbonyl for sulfur dioxide is defined by the dissociation constant Kd of its carbonyl bisulfite. Among wine compounds, acetaldehyde which carbonyl bisulfite Kd is 2.4×10-3 mM is considered as the one with the highest affinity for SO2. Acetaldehyde origins is both an intermediary in alcoholic fermentation pathway but could also be produced from ethanol oxidation. Diacetyl (2,3 butanedione), has also a microbiological origin and an appreciable affinity for sulfur dioxide (carbonyl bisulfite Kd is 0.1 mM). Moreover, diacetyl is able to be produced but also reduced by yeasts and their potential sensory impact on red wines has already been established.
To evaluate if acetaldehyde and diacetyl could be at the origin of sensory specificities in wines without SO2, sensory profiles were classically determined, using sensory descriptors generation and panel training, on different modalities illustrating average levels of diacetyl, acetaldehyde and free SO2 in wines with or without sulfites and prepared from the same commercial without sulfites wine. Such an approach allowed to reveal that acetaldehyde and free SO2 were involved in the perception of “Coolness” depending of their concentrations in wines with and without added SO2. Diacetyl, meanwhile, impacted fruity aroma perception in wines with added SO2 and was responsible for sensory differences between wine with and without added SO2. Thus, the addition of diacetyl and SO2, at average concentrations found in wines with SO2, in a wine without added SO2 led to a decrease of “Fresh Black Fruits”, “Fresh Raspberry” and “Coolness” perception and an increase of “Jammy Black Fruits” perception.  These results are in line with sensory differences already highlighted in studies dealing with global olfactive characterization of reds wines with and without sulfites and help to explain red wines without sulfites sensory specificities