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Traditional sour beers are produced by spontaneous fermentations involving numerous yeast and bacterial species. One of the traits that separates sour beers from ales and lagers is the high concentration of organic acids such as lactic acid and acetic acid, which results in reduced pH and increased acidic taste. Several challenges complicate the production of sour beers through traditional methods. These include poor process control, lack of consistency in product quality, and lengthy fermentation times. This review summarizes the methods for traditional sour beer production with a focus on the use of lactobacilli to generate this beverage. In addition, the review describes the use of selected pure cultures of microorganisms with desirable properties in conjunction with careful application of processing steps. Together, this facilitates the production of sour beer with a higher level of process control and more rapid fermentation compared to traditional methods. [ABSTRACT FROM AUTHOR]

Increasing popularity of sour beer urges the development of novel solutions for controlled fermentations both for fast acidification and consistency in product flavor and quality. One possible approach is the use of Saccharomyces cerevisiae in co-fermentation with Lactobacillus species, which produce lactic acid as a major end-product of carbohydrate catabolism. The ability of lactobacilli to ferment beer is determined by their capacity to sustain brewing-related stresses, including hop iso-α acids, low pH and ethanol. Here, we evaluated the tolerance of Lactobacillus brevis BSO464 and Lactobacillus buchneri CD034 to beer conditions and different fermentation strategies as well as their use in the brewing process in mixed fermentation with a brewer's yeast, S. cerevisiae US-05. Results were compared with those obtained with a commercial Lactobacillus plantarum (WildBrewTM Sour Pitch), a strain commonly used for kettle souring. In pure cultures, the three strains showed varying susceptibility to stresses, with L. brevis being the most resistant and L. plantarum displaying the lowest stress tolerance. When in co-fermentation with S. cerevisiae , both L. plantarum and L. brevis were able to generate sour beer in as little as 21 days, and their presence positively influenced the composition of flavor-active compounds. Both sour beers were sensorially different from each other and from a reference beer fermented by S. cerevisiae alone. While the beer produced with L. plantarum had an increased intensity in fruity odor and dried fruit odor, the L. brevis beer had a higher total flavor intensity, acidic taste and astringency. Remarkably, the beer generated with L. brevis was perceived as comparable to a commercial sour beer in multiple sensory attributes. Taken together, this study demonstrates the feasibility of using L. brevis BSO464 and L. plantarum in co-fermentation with S. cerevisiae for controlled sour beer production with shortened production time. [ABSTRACT FROM AUTHOR]

Sour beer is beer with an intentionally sour taste. In traditionally produced sour beer, the acidic character results from spontaneous, mixed fermentation where different bacteria and yeast species participate. These complex fermentations take years to complete and can be difficult to control. Owing to the increasing interest in sour beer and challenges related to commercial sour beer brewing, alternative production methods are being explored. In the current paper, pre‐fermentation with lactic acid bacteria (LAB) was investigated as a timesaving and controllable strategy for the production of sour beer. Four beers were produced with either biological or chemical acidification of wort, and a reference beer was produced with no acidification. Volatile compounds and organic acids were analysed by headspace gas chromatography and high‐performance liquid chromatography to explore any contribution from LAB to the composition of beer. Finally, descriptive sensory analysis was performed to evaluate the sensory contribution from LAB. A significant effect was observed from LAB pre‐fermentation, with respect to both volatile compounds (e.g. reduced production of 2‐methyl‐1‐butanol) and organic acids (e.g. production of acetic acid). Biological acidification by LAB pre‐fermentation had a significant impact on the sensory character of beer. This sensory impact did, however, not surpass that obtained by chemical acidification, as few significant differences were found between biologically and chemically acidified beers. © 2019 The Institute of Brewing & Distilling [ABSTRACT FROM AUTHOR]

Xylooligosaccharides (XOS) from woody biomass were evaluated as a substrate for secondary lactic acid bacteria (LAB) fermentation in sour beer production. XOS were extracted from birch ( Betula pubescens ) and added to beer to promote the growth of Lactobacillus brevis BSO 464. Growth, pH, XOS degradation, and metabolic products were monitored throughout fermentations, and the final beer was evaluated sensorically. XOS were utilized, metabolic compounds were produced (1800 mg/L lactic acid), and pH was reduced from 4.1 to 3.6. Secondary fermentation changed sensory properties significantly, and the resulting sour beer was assessed as similar to a commercial reference in multiple attributes, including acidic taste. Overall, secondary LAB fermentation induced by wood-derived XOS provided a new approach to successfully produce sour beer with reduced fermentation time (from 1-3 years to 4 weeks). The presented results demonstrate how hemicellulosic biomass can be valorized for beverage production and to obtain sour beer with improved process control.