MALOLACTIC FERMENTATION– A REVIEW OF RECENT RESEARCH ON TIMING OF INOCULATION AND POSSIBLE YEAST-BACTERIA COMBINATIONS

Despite a considerable research effort, the malolactic fermentation (MLF) process remains an imperfectly controlled process and at times MLF can be difficult to get started. One possible explanation for this difficulty is that the wine may be lacking essential nutrient factors for the lactic acid bacteria. Another possible argument is that inhibitory substances are accumulated in wine. Sulfur dioxide and alcohol concentrations and pH have been included among the most significant parameters influencing the growth of malolactic bacteria in wine. King and Beelman suggested that the growth of Oenococcus oeni during alcoholic fermentation might be retarded by the production of toxic compounds by yeasts other than ethanol and sulfur dioxide. Moreover, the malolactic fermentability of wines produced from the same must differ according the yeast strain used in alcoholic fermentation. Previous studies have shown the inhibition of malolactic starter cultures by active growing yeasts due to the production of high levels of SO2 during the early stage of alcoholic fermentation and the effect of acetic acid formed by Kloeckera yeasts and some lactobacilli on growth of Saccharomyces. The goal of our recent investigations is to better understand these interactions, to quantify the nutrient demand by yeast and the nutrient requirements of wine lactic acid bacteria, and to determine whether there are other synergistic interactions between S. cerevisiae and O. oeni in wine. A better understanding of these aspects of wine microorganism physiology will allow us to better match combinations of yeast and bacteria starter cultures with grape varieties, and select the timing of yeast and bacteria inoculations