Implication of acetic acid in the induction of slow/stuck grape juice fermentations and inhibition of yeast by Lactobacillus sp.

The impact of acetic acid and its suggested role in inducing slow/stuck alc oholic fermentations was studied. The inhibitory effect of acetic acid agai nst Saccharomyces cerevisiae was dependent on the strain as evidenced by th e wide range of minimum inhibitory concentrations observed (4.5 to 7.5 g/L) . Lactobacillus kunkeei, a spoilage bacterium previously determined to caus e slow/stuck alcoholic fermentations, produced 4 to 5 g/L acetic acid when grown in a Chardonnay grape juice. Daily addition of sterile-filtered solut ions of acetic acid to Riesling and Chardonnay fermentations at the same ra te produced by L. kunkeei delayed completion of the fermentations. Although the Riesling fermentations with acetic acid eventually became dry (<2 g/L fermentable carbohydrate), Chardonnay fermentations became stuck. Yeast pop ulations in the Chardonnay grape juices with or without acetic acid exceede d 10(7) cfu/mL and were not different during fermentation. This finding was in contrast to previous inhibition studies between S. cerevisiae and L. ku nkeei where the yeasts studied did not enter logarithmic growth in juices i noculated with the bacterium. Therefore, excessive production of acetic aci d can slow alcoholic fermentations but does not solely account for the bact erial inhibition of yeast.