Jessika De Clippeleer

Hopping technology in relation to beer bitterness consistency and flavor stability

The fate of α-acids, iso-α-acids, and their chemically modified variants was monitored in pilot brews as a function of hopping regime and beer aging. HPLC analysis indicates that α-acids, iso-α-acids, and dihydroiso-α-acids in beer are not stable during forced aging. This is reflected further in the sensory performance of these beers. Beer exclusively bittered with tetrahydroiso-α-acids was completely stable, in terms of hop components, under the experimental conditions employed. In addition, overall flavor stability was significantly improved. These results provide further evidence that hop-derived bitter acids, including the light-stable dihydroiso-α-acids, could play an important role in beer flavor deterioration during storage.

Fermentation assays reveal differences in sugar and (off-) flavor metabolism across different Brettanomyces bruxellensis strains

Abstract Brettanomyces (Dekkera) bruxellensis is an ascomycetous yeast of major importance in the food, beverage and biofuel industry. It has been isolated from various man‐made ecological niches that are typically characterized by harsh environmental conditions such as wine, beer, soft drink, etc. Recent comparative genomics studies revealed an immense intraspecific diversity, but it is still unclear whether this genetic diversity also leads to systematic differences in fermentation performance and (off‐)flavor production, and to what extent strains have evolved to match their ecological niche. Here, we present an evaluation of the fermentation properties of eight genetically diverse B. bruxellensis strains originating from beer, wine and soft drinks. We show that sugar consumption and aroma production during fermentation are determined by both the yeast strain and composition of the medium. Furthermore, our results indicate a strong niche adaptation of B. bruxellensis, most clearly for wine strains. For example, only strains originally isolated from wine were able to thrive well and produce the typical Brettanomyces‐related phenolic off‐flavors 4‐ethylguaiacol and 4‐ethylphenol when inoculated in red wine. Sulfite tolerance was found as a key factor explaining the observed differences in fermentation performance and off‐flavor production. Sequence analysis of genes related to phenolic off‐flavor production, however, revealed only marginal differences between the isolates tested, especially at the amino acid level. Altogether, our study provides novel insights in the Brettanomyces metabolism of flavor production, and is highly relevant for both the wine and beer industry.