Malolactic fermentation as a technique for the deacidification of hard apple cider

Malolactic fermentation (MLF), the conversion of malate to lactate, is an important process leading to the deacidification of hard apple cider. MLF is dependent on the levels of inhibitory factors such as sulfur dioxide and ethanol. To assess the effect of these 2 factors on MLF, hard apple cider was produced from pasteurized, unfiltered apple cider (Malus domestica cvs Red Delicious, Golden Delicious, Braeburn, and Fuji). Apple cider was treated with 2 levels of sulfur dioxide (50 and 80 ppm) and then fermented using Saccharomyces cerevisiae montrachet. After the primary fermentation, 1 set of the samples remained unadjusted and 100% ethyl alcohol was used to adjust other sets of samples to 7%, 9%, or 11% (v/v) ethanol. Following the ethanol adjustment, Oenococcus oeni MCW was used to initiate the MLF in half of the samples. Cider parameters monitored throughout the fermentations included organic acid content, titratable acidity, pH, ethanol production, and sugar content. Since samples containing either sulfur dioxide level had similar sugar utilization rates and ethanol production it was concluded that sulfur dioxide had no effect on the primary fermentation. Sulfur dioxide content was shown to have an impact on MLF. There was no difference in the rate of malic acid consumption, but lactic acid production was faster in the 50-ppm sulfur dioxide samples. MLF was not inhibited by ethanol content.