Kinetics of sugars, organic acids and acetaldehyde during simultaneous yeast-bacterial fermentations of white wine at different pH values

Abstract

Successfully inducing malolactic fermentation in the production of grape wines can be challenging, especially in wines with multiple inhibitors such as low pH values and high ethanol concentrations. In the present study, the kinetics of several chemicals of enological relevance was studied in Chardonnay vinified by traditional, consecutive alcoholic (AF) and malolactic fermentations (MLF), and simultaneous AF/MLF, where bacteria were co-inoculated with yeast. The Chardonnay must was adjusted to four pH values (3.2, 3.35, 3.5 or 3.65), and the concentrations of sugars, organic acids as well as acetaldehyde were followed throughout the fermentations. The degradation of glucose and fructose was slower at the lowest must pH value (3.2) but independent from the time point of bacterial inoculation. In all cases, malolactic conversion was faster after yeast-bacterial co-inoculation and was completed in simultaneous treatments at pH values of 3.35–3.65, and consecutive treatments at pH 3.5 and 3.65. No statistically significant difference was observed among the final acetic acid concentrations among all inoculation and pH treatments, but there was a trend towards higher acetic acid residues in wines produced by co-inoculation, especially at high pH values. Overall, simultaneous AF/MLF allowed for greatly reduced fermentation times, but the must pH remained a strong factor for fermentation success and determined the final concentration of various wine components. The time point of inoculation influenced formation and degradation kinetics of organic acids and acetaldehyde considerably, and these are of relevance for vinification decisions.