Onderzoek naar de rol van prioriteitseffecten bij de samenstelling van microbiële gemeenschappen in vatgerijpte zure bieren

Sour beers obtained through maturation of conventionally fermented beers in wooden barrels are becoming increasingly popular in the (craft) beer community due to their noteworthy balance between sourness, aroma and flavour complexity. However, severe lack of predictability and control of the process often leads to inconsistent results that can lead to substantial financial losses. Recent studies suggest that barrels represent an important factor leading to batch-to-batch variation, particularly as the inner surfaces of barrels can be covered by a diverse microbial community that unfavourably affects the beer chemistry and sensory characteristics. Previous research has shown that differences in species arrival order, also known as "priority effects", can significantly impact both the structure and functioning of ecological communities. However, the underlying mechanisms which could explain complex community dynamics during barrel ageing and how they affect beer chemistry still remain unclear. In this thesis, we addressed this research question using an experimentally tractable model system mimicking the barrel ageing process, which incorporated a synthetic microbial community consisting of four bacterial species (Acetobacter malorum, Gluconobacter oxydans, Levilactobacillus brevis, and Pediococcus damnosus) and four fungal species (Brettanomyces bruxellensis, Candida friedrichii, Pichia membranifaciens, and Saccharomyces cerevisiae). We first developed probe-based qPCR assays for detection and quantification of the eight microbial community members. Next, we evaluated the impact of prior inoculation of Acetobacter malorum and Brettanomyces bruxellensis on microbial community establishment and beer chemistry during 46 weeks of wood maturation which showed strong, albeit transient, priority effects. Although priority effects were transient, they had a long-lasting impact on beer chemistry that persisted throughout wood maturation. Microbial interactions were further evaluated in a pairwise manner, and showed that most, but not all, community level interactions could be explained by the results of the pairwise interactions. Ultimately, the results obtained in this PhD thesis may inform the development of a control strategy to steer microbial community composition in the production of barrel-aged sour beers and accomplish a consistent production, thereby paving the way for the production of a new generation of sour beers.