Secondary lactic acid bacteria fermentation with wood-derived xylooligosaccharides as a tool to expedite sour beer production.

Xylooligosaccharides (XOS) from woody biomass were evaluated as 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 valorised for beverage production, and to obtain sour beer with improved control.