Gas–liquid transfer of aroma compounds during winemaking fermentations

Abstract

We precisely monitored the production kinetics of 16 volatile carbon compounds corresponding to the predominant higher alcohols and esters produced during the alcoholic fermentation of wine using an on-line GC system. We studied the gas–liquid partitioning of isobutanol, isoamyl acetate and ethyl hexanoate and showed that CO2 stripping had no impact on the partition coefficient (ki). We formulated a predictive model for ki changes during the fermentation and calculated the gas–liquid balances of these volatile compounds throughout the entire fermentation process. Losses in the off-gas were highly compound-dependent. They were negligible for higher alcohols but very high for esters, with losses of up to 70% for ethyl hexanoate at 30 °C. The rates of volatile compound production, accumulation and loss could also be calculated with high precision. Loss rates were maximal at the end of fermentation, indicating that high final temperatures, although helpful in avoiding sluggish fermentations, can be very detrimental to aroma losses.