In this work we were focused on the influence of lactic acid and propionic acid bacteria with antimicrobial effects on quality of alcohol free beer. In the first part, we optimized cultivation parameters for Lactobacillus amylolyticus and Propionibacterium freudenreichii subsp. freudenreichii in order to maximize the yield of organic acids. With L. amylolyticus we were able to produce up to 25 g/l of lactic acid. We used acidified wort to lower the pH of wort for production of alcohol free beer and test it for antimicrobial properties, but we could not see any inhibition against beer spoiling bacteria Lactobacillus brevis. Next, we used acidified wort in cold contact fermentation for production of alcohol free beer. Our hypothesis was that bacteria could lower Strecker aldehydes in wort. We focused on three flavor active aldehydes 2-methylbutanal, 3-methylbutanal and methional. With propionic acid bacteria, we were able to bind Strecker aldehydes on bacteria surface or their extracellular polymers. When using bacteria, most of Strecker aldehydes were below sensory threshold.
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