Lactic acid bacteria fermentation of wort as a tool to add functionality in malting, brewing and novel beverages
University College Cork
This thesis addresses the investigation of several strains of LAB for biopreservation using in vitro and in situ studies, as well as for acidification of wort to be applied during sour brewing and as novel beverages. The impact of bacterial carboxylic acids, with emphasis on phenolic antifungal compounds, was assessed against Fusarium culmorum, a common fungal spoilage organism in malt. The contribution of phenolic acids to the overall fungal inhibition was found to be limited unless combined with lactate and acetate in a low pH environment, suggesting their contribution in a complex, synergistic mechanism. An antifungal ingredient was produced by fermenting wort with Lactobacillus brevis R2Δ. When this substrate was applied on barley during steeping and germination, it significantly reduced the amount of fusaria infection, detoxified the substrate and increased the extract yields. To enrich even more bacterial metabolites in wort, an extension of acidification could be achieved by promoting the release of free amino nitrogen through a longer proteolytic rest during mashing or the addition of protease. Up to 12.8 g/L LA were achieved in buffered-wort before nutrient-related deficiencies inhibited further acidification. A comparison between acidification methods during production of sour beers showed that, depending on the time point of souring, the beers differed significantly in their processability and flavour profile. Acidification of wort before the boil step was chosen as the preferred technique due to its safer implementation and minimal effect on organoleptic properties. Finally, the sensory profile of fermented, non-alcoholic malt-based beverages revealed that lactic fermentation increased acidity and flavour complexity of these drinks, and reduced compounds that elicit “malty” notes, while increasing the “dairy”, “bready”, and “honey” character. Forced ageing led to an increase in typical beer off-flavours in all samples, but fermented beverages showed a better organoleptic stability than the unfermented control.
Lactic acid bacteria , Fermentation , Malt extract , Malting , Brewing , Novel beverages
Peyer, L. 2017. Lactic acid bacteria fermentation of wort as a tool to add functionality in malting, brewing and novel beverages. PhD Thesis, University College Cork.