Formation and Degradation of Diacetyl in Wine During Alcoholic Fermentation with Saccharomyces cerevisiae Strain EC1118 and Malolactic Fermentation with Leuconostoc oenos Strain MCW

Diacetyl accumulates in wine during alcoholic and malolactic fermentation (MLF). In an effort to understand the factors influencing the final diacetyl content of wine, we followed the changes in diacetyl concentration in Cabernet Sauvignon and Pinot noir wines throughout alcoholic fermentation with the widely used wine yeast Saccharomyces cerevisiae strain EC1118, during MLF with Leuconostoc oenos strain MCW, and during storage. The effect of presence of yeast on the evolution of diacetyl concentration during MLF was investigated using the following treatments: ( 1 ) wine; ( 2 ) wine plus 60 mg/L sulfur dioxide; ( 3 ) sterile filtered wine; ( 4 ) wine plus Leuc. oenos strain MCW; and ( 5 ) sterile filtered wine plus Leuc. oenos strain MCW. Diacetyl concentrations increased linearly during alcoholic fermentation and then declined. No reduction in diacetyl concentration occurred after sterile filtration of wine or addition of 60 mg/L SO 2 to Pinot noir wine. An increase in diacetyl concentrations was observed two days after inoculation with malolactic cultures. Presence of S. cerevisiae EC1118 in wines inoculated with Leuc. oenos strain MCW resulted in lower diacetyl concentration throughout the course of MLF. Final concentration of diacetyl in MLF wines was brought to a concentration below sensory threshold about 20 days after completion of malolactic fermentation, both in the presence and absence of S. cerevisiae . Utilization of diacetyl by Leuc. oenos strain MCW, as well as other strains, was demonstrated.