Yeast stability tests on dessert wines

California musts were fortified at various stages of fermentation to test the applicability of the DELLE equation, i. e., dependency of inhibition of fermentation on the sum (DELLE units) of the percentage of sugar plus 4.5 times the percentage of alcohol, by volume. For fortification, alcohol was added to fermenting musts to give final concentrations from 11 to 19 percent. The resultant DELLE units, calculated from chemical analyses of lots in which fer,mentation was inhibited, were dependent upon stage of fermentation at which .fortified, variety of must, and strain of wine yeast. Higher DELLE units were required for stabiHty when the fortification was made in the late stages of fermentation, compared to early stages, and Chardonnay must required !higher DELLE units for stability than did Sauvignon blanc or Semillon musts. Montr,achet and Champagne strains of Sacchiaromyces cerevisiae var. ellipsoideus required lower DELLE units to give complete inhibition of fermentation than did Burgundy strain

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

The effect of nitrogen deficiency and sulfur containing amino acids on the control of the reduction of sulfate to hydrogen sulfide by wine yeasts.

The effect of nitrogen deficiency and sulfur containing amino acids on the control of the reduction of sulfate to hydrogen sulfide by wine yeasts

Increased production of n-propanol by yeast strain having an impaired ability to form hydrogen sulfide.

Increased production of n-propanol by yeast strain having an impaired ability to form hydrogen sulfide