Simultaneous and successive inoculations of yeasts and lactic acid bacteria on the fermentation of an unsulfited Tannat grape must

Abstract

Interactions between yeasts and lactic acid bacteria are strain specific, and their outcome is expected to change in simultaneous alcoholic - malolactic fermentations from the pattern observed in successive fermentations. One Oenococcus oeni strain Lalvin VP41™ was inoculated with two Saccharomyces cerevisiae strains either simultaneously, three days after the yeast inoculation, or when alcoholic fermentation was close to finish. Early bacterial inoculations with each yeast strain allowed for the growth of the bacterial populations, and the length of malolactic fermentation was reduced to six days. Alcoholic fermentation by Lalvin ICV D80® yeast strain left the highest residual sugar, suggesting a negative effect of the bacterial growth and malolactic activity on its performance. In sequential inoculations the bacterial populations did not show actual growth with either yeast strain. In this strategy, both yeast strains finished the alcoholic fermentations, and malolactic fermentations took longer to finish. Lalvin ICV D80® allowed for higher viability and activity of the bacterial strain than Fermicru UY4® under the three inoculation strategies. This was beneficial for the sequential completion of both fermentations, but negatively affected the completion of alcoholic fermentation by Lalvin ICV D80® in the early bacteria additions. Conversely, Fermicru UY4®, which was rather inhibitory towards the bacteria, favored the timely completion of both fermentations simultaneously. As bacteria in early inoculations with low or no SO2 addition can be expected to multiply and interact with fermenting yeasts, not only are the yeast-bacterium strains combination and time point of the inoculation to be considered, but also the amount of bacteria inoculated.

Influence of malolactic bacteria inoculation scenarios on the efficiency of the vinification process and the quality of grape wine from the Central European region

“…This result confirms the observations of other authors who have reported no disturbances to alcoholic fermentation when employing similar bacterial inoculation variants [1,14,19,30,39,43]. Although some authors have pointed to disturbances in alcoholic fermentation attributed to the activity of malolactic bacteria, these have concerned the viability of the yeast-a reduction in their growth dynamics and metabolic activity-with no significant influence on the final ethanol content in wines [7,34]. Besides ethanol and CO 2 , glycerol is also synthesized during alcoholic fermentation.…”

“…However, it must be emphasized that both the total acidity (9.38-12.14 g/L) and the malic acid concentration (6.54-9.5 g/L) were higher than other grapes presented in the literature (Table 2) [1,8,14,18,19,30,34,39,43]. …”

“…Recently, an increasing number of authors have reported small differences in the acetic acid concentrations of wines produced using O. oeni bacteria. Almost always, the level of acetic acid has been below the admissible limit and did not affect the quality and aroma of the wines [5,18,30,34]. In our study, when evaluating the effect of MLF on the final concentration of acetic acid, the worst results were obtained for the spontaneous malolactic fermentation variant.…”

“…The same variant had the greatest reduction in total acidity (from 2.99 to 3.68 g/L) and the greatest increase in pH (from 0.34 to 0.43) (Table 5). Likewise, Munoz et al [34] have reported a greater reduction in the level of malic acid with simultaneous alcoholic and malolactic fermentations than in the case of sequential bacteria inoculation (in the middle and at the end of alcoholic fermentation). Similar observations have also been made by Jussier et al [18] in the production of Chardonnay from grapes grown in cool-climate regions.…”

“…The MLF process was found to have a significant effect on the residual sugar level: Significantly lower concentrations of residual sugars were noted in the wines obtained by applying the inoculated (simultaneous or sequential) MLF; this is a great advantage of these MLF processes. The lower concentration of sugars enhances the microbiological stability of the wine and protects it from microbiological synthesis of undesirable metabolites that can contribute to spoilage [34].…”