Implication of Acetic Acid in the Induction of Slow/Stuck Grape Juice Fermentations and Inhibition of Yeast by Lactobacillus sp

Abstract

The impact of acetic acid and its suggested role in inducing slow/stuck alcoholic fermentations was studied. The inhibitory effect of acetic acid against Saccharomyces cerevisiae was dependent on the strain as evidenced by the wide range of minimum inhibitory concentrations observed (4.5 to 7.5 g/L). Lactobacillus kunkeei, a spoilage bacterium previously determined to cause slow/stuck alcoholic fermentations, produced 4 to 5 g/L acetic acid when grown in a Chardonnay grape juice. Daily addition of sterile-filtered solutions of acetic acid to Riesling and Chardonnay fermentations at the same rate 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 populations in the Chardonnay grape juices with or without acetic acid exceeded 10⁷ cfu/mL and were not different during fermentation. This finding was in contrast to previous inhibition studies between S. cerevisiae and L. kunkeei where the yeasts studied did not enter logarithmic growth in juices inoculated with the bacterium. Therefore, excessive production of acetic acid can slow alcoholic fermentations but does not solely account for the bacterial inhibition of yeast.