A mathematical model of the link between growth and L-malic acid consumption for five strains of Oenococcus oeni

In winemaking, after the alcoholic fermentation of red wines and some white wines, L-malic acid must be converted into L-lactic acid to reduce the acidity. This malolactic fermentation (MLF) is usually carried out by the lactic acid bacteria Oenococcus oeni. Depending on the level of process control, selected O. oeni is inoculated or the natural microbiota of the cellar is used. This study considers the link between growth and MLF for five strains of O. oeni species. The kinetics of growth and L-malic acid consumption were followed in modified MRS medium (20 °C, pH 3.5, and 10 % ethanol) in anaerobic conditions. A large variability was found among the strains for both their growth and their consumption of L-malic acid. There was no direct link between biomass productivities and consumption of L-malic acid among strains but there was a link of proportionality between the specific growth of a strain and its specific consumption of L-malic acid. Experiments with and without malic acid clearly demonstrated that malic acid consumption improved the growth of strains. This link was quantified by a mathematical model comparing the intrinsic malic acid consumption capacity of the strains

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 to be 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 parameter 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

Survey about the microbiological features, the oenological performance and the influence on the character of wine of active dry yeast employed as starters of wine fermentation

In this work we compared the microbiological features and the fermentative aptitude of 29 different ADY available on the Italian market. Each sample was essayed by microbiological analysis and fermentations in 3 different grape musts. Attention was focused on the presence of wine spoilage microorganisms inside ADY, and on the degradation/production of secondary metabolites having a relevant impact on the quality of win

Influence of different yeast/lactic acid bacteria combinations on the aromatic profile of red Bordeaux wine

BACKGROUND The typical fruity aroma of red Bordeaux wines depends on the grape variety but also on microbiological processes, such as alcoholic and malolactic fermentations. These transformations involve respectively the yeast Saccharomyces cerevisiae and the lactic acid bacterium Oenococcus oeni. Both species play a central role in red winemaking but their quantitative and qualitative contribution to the revelation of the organoleptic qualities of wine has not yet been fully described. The aim of this study was to elucidate the influence of sequential inoculation of different yeast and bacteria strains on the aromatic profile of red Bordeaux wine. RESULTS All microorganisms completed fermentations and no significant difference was observed between tanks regarding the main oenological parameters until 3 months' aging. Regardless of the yeast strain, B28 bacteria required the shortest period to completely degrade the malic acid, compared to the other strain. Quantification of 73 major components highlighted a specific volatile profile corresponding to each microorganism combination. However, the yeast strain appeared to have a predominant effect on aromatic compound levels, as well as on fruity aroma perception. CONCLUSION Yeasts had a greater impact on wine quality and have more influence on the aromatic style of red wine than bacteria