94-5 |
Influence of lactic acid bacteria on malt whisky fermentations |
F. G. PRIEST, International Centre for Brewing & Distilling, Heriot Watt Univ., John Muir Bldg., Edinburgh, EH14 4AS, United Kingdom During the production of Scotch malt whisky the wort is not boiled and consequently the fermentation contains a natural bacterial flora. We have been examining the types of bacteria present, their development during the fermentation and their contributions to the process and product. The bacterial flora in a malt whisky distillery is remarkably stable. Over a 12-month period we generally isolated the same bacteria from late fermentation samples from Glenkinchie Distillery, notably strains of Lactobacillus brevis, Lactobacillus ferintoshensis, Lactobacillus fermentum and Lactobacillus paracasei. In a survey of fermentation samples from 23 distilleries, L. brevis, L. fermentum and L. paracasei were the most common bacteria with L. ferintoshensis, Lactobacillus pentosus and Lactobacillus plantarum more rarely encountered. However, DNA fingerprinting revealed that different strains inhabited different distilleries, supporting the notion that distilleries generate distinct flora. Denaturing gradient gel electrophoresis (DGGE) detects bacteria without prior growth on laboratory media. DGGE revealed that the initial bacterial community in the fermentation is diverse and includes cocci and the thermotolerant bacterium Bacillus coagulans. As the fermentation proceeds the heterogeneity declines and, after 45 h one or two strains dominate, often to be replaced by homofermentative bacteria related to Lactobacillus acidophilus in the late stages. Lactic acid from B. coagulans could improve the extract from the mash by lowering the pH towards the optimum for beta-amylase. In the fermentation some lactobacilli contribute to flavour by decarboxylating cinnamic acids from barley cell walls into vinylphenol and vinylguaiacol. Finally, sensory analysis of new-make spirits derived from mixed fermentations with different lactobacilli attributed positive sensory notes such as “estery”, “leafy” and “fruity” to the presence of the organisms.
Session 94, Challenges of converting carbohydrates into flavors by fermentation
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