Effect On The Quality Of ’Cabernet Gernischt’ Dry Red Wine By Oenococcus Oeni OMEGA

Malolactic fermentation（MLF） conducted by Oenococcus oeni is an indispensable step in the production of the finest dry red wine, which can effectively decrease acidity, improve the quality of aroma and increase biological stability. It is difficult to ensure the consistency of wines through spontaneous MLF, while artificial inoculation can not only start fermentation fleetly and steadily, but also ensure the success of MLF effectively. In this research, ’Cabernet Gernischt’ grapes in Hexi corridor of Gansu province were used as raw materials, O.oeni OMEGA was inoculated in the must at the beginning, middle and the end of the alcoholic fermentation to study the effect of different inoculation regimes on MLF. The optimal process conditions of MLF were also determined in the study. Finally, to provide theoretical basis for improving the quality of ’Cabernet Gernischt’ dry red wine, the impact of MLF on wine quality was explored, both the changes of physical-chemical parameters and volatile compounds were compared between wines with MLF conduced at optimal conditions and without MLF. The main results were as follows:1. The results of different inoculation regimes to conduct MLF showed that fermentation can successfully complete in all three MLF inoculation treatments including inoculated at the beginning, middle and the end of the alcoholic fermentation. AF was all completed after 9 days, but the completion time of MLF was different, there were finished at 9、15、18 days respectively in three inoculation regimes and the co-inoculation can significantly reduce the overall vinification time to less than 2 weeks.2. After the end of MLF, the concentrations of volatile acid produced in all three treatments were increased which the content was the co-inoculation>mid-inoculation>post-inoculation, but even in the co-inoculation, the highest value was only 0.70 g/L, within the normal requirements of less than 1.2 g/L in GB/T 15038-2006. After fermentation, the flavor balance index in co-inoculation wine samples were 7.39, higher than the mid-inoculation 6.55 and post-inoculation 6.98.3. The analysis of volatile aroma compounds in three different inoculation regimes showed that there were variations in the concentration of ester compounds after MLF, and the content of ethyl esters was highest in the co-inoculation regimes, which produced more fruity aroma than other inoculation regimes. Principal component analysis showed that wine samples used co-inoculation regimes were obvious distinction from other wine samples. Thus, it is likely proved that the co-inoculation regime is a good choice to conduct MLF.4. The flavor balance index after fermentation was used as evaluation, through the orthogonal experiments, the sequence of factors to conduct co-inoculation MLF in ’Cabernet Gernischt’ wine were SO₂>fermentation temperature>pH>inoculation dosage, and the optimal conditions were SO₂ 30 mg/L, fermentation temperature 20 ℃, pH 3.6 and inoculation dosage 10 mg/L. After completion of the fermentation under these conditions, the flavor balance index was 7.59.5. The total content of esters were significantly increased, while alcohols and acids were decreased in ’Cabernet Gernischt’ wine after MLF. In addition, compounds such as ethyl lactate, decanoic acid-3-methylbutyl ester and 2,3-butanediol were new addition to the total aromas, while compounds such as ethyl hexanoate, 2-methylcaproic acid and 1-tetradecanol were disappeared.6. The results of sensory evaluation showed that the score in wine samples after MLF（87.50） higher than the score in wines without MLF（82.85）, which further indicated that the quality of wine was enhanced after MLF.