The precursor to diacetyl, α-acetolactate, is produced by yeast during fermentation. The long secondary fermentations carried out during lager brewing, for example, are primarily carried out to remove diacetyl from the system. Consequently, the brewing process is carefully managed to minimize diacetyl levels. In lager beers, which are characterized by fresh and clean flavor profiles, diacetyl is almost invariably considered as an off flavor. In fermented beverages, diacetyl notes may be perceived positively or negatively depending on the product and style. Adaptive laboratory evolution appears to be a natural, simple and cost-effective strategy for diacetyl control in brewing.ĭiacetyl (2,3-butanedione) is a vicinal diketone that imparts a distinct butter/butterscotch flavor and is an important component in the flavor profile of many foods. This mutation is known to confer general tolerance to sulfonylurea compounds, and is the most likely cause of the improved tolerance. Whole-genome sequencing revealed a non-synonymous SNP in the ILV2 gene of the adapted isolate. Diacetyl levels were over 60% lower at the end of primary fermentation relative to the non-adapted lager yeast and no significant change in fermentation performance or volatile flavor profile was observed due to the adaptation.

Pilot-scale fermentation was carried out with one isolate and results confirmed the positive effect of chlorsulfuron adaptation. Initial screening of 7 adapted isolates showed a lower level of diacetyl during wort fermentation and no apparent negative influence on fermentation rate or alcohol yield. Cells were exposed repeatedly to a sub-lethal level of chlorsulfuron, which inhibits the acetohydroxy acid synthase responsible for α-acetolactate production. Here, we investigated the possibility of lowering beer diacetyl levels through evolutionary engineering of lager yeast for altered synthesis of α-acetolactate, the precursor of diacetyl.

Its typical buttery flavor is considered as an off flavor in lager-style beers, and its removal has a major impact on time and energy expenditure in breweries.

Diacetyl contributes to the flavor profile of many fermented products.

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