Biological de-sugaring of grape musts to adjust the alcoholic strength of wine

Climate change is having an ever-increasing impact on the physico-chemical composition of grapes, with ever-lower acidity and higher sugar levels. These high sugar levels are not without consequences for the alcoholic and malolactic fermentations, as well as for the physico-chemical and aromatic characteristics of the wines. Reducing the alcoholic strength is part of an approach aimed at meeting consumer expectations for more dietary, lighter or lower-alcohol wines (9 to 13% Vol.). This correction also helps rebalance the mouthfeel of wines by reducing the burning side of ethanol.

The technology presented here involves adding a fraction of the must previously desugared biologically to the must whose alcoholic strength is to be lowered.

Biological desugaring consists in using yeasts classically used in oenology in a fermenter under conditions of temperature, aeration, agitation and nitrogen nutrition defined to consume all the sugar in a minimum of time.  Sacharomyces cerevisiae yeasts are crabtree positive, which means that whatever the aeration conditions, they will always produce alcohol. The ingenuity of the process consists in managing the yeast culture conditions to limit the crabtree effect, with total desugaring and and a very low alcohol concentration production in less than 72 hours.

In all the trials, almost all the sugar in the must was consumed, and the alcohol content of the desugared must was around 1% Vol. During the desugaring phase, yeast metabolism leads to a sharp drop in pH, which must be regulated to avoid blocking yeast activity at too low a pH. In any case, acetic acid production remains limited.

Once the yeast-rich desugared must has been reincorporated into the initial tank, fermentation proceeds more rapidly as the alcoholic strength drops. On finished wines, organically desugared wines have a pH 0.1 to 0.3 pH units lower than the control, thus rebalancing acidity. Apart from a drop in alcoholic strength, no significant changes in physicochemical composition or aromatic compound content were observed in the organically desugared wines. Organoleptic analysis shows significant yeast notes in the dealcoholized wines, and the yeast load should be reduced by centrifugation or sedimentation before reincorporation of the desugared must. No objectionable change in organoleptic quality of organically desugared wines. Optimization of both the desugaring process and vinification is still necessary before this technology can be deployed on a large scale.