Saccharomyces cerevisiae variety diastaticus friend or foe?—spoilage potential and brewing ability of different Saccharomyces cerevisiae variety diastaticus yeast isolates by genetic, phenotypic and physiological characterization

Abstract

Saccharomyces cerevisiae variety diastaticus is generally considered to be an obligatory spoilage microorganism and spoilage yeast in beer and beer-mixed beverages. Their super-attenuating ability causes increased carbon dioxide concentrations, beer gushing and potential bottle explosion along with changes in flavor, sedimentation and increased turbidity. This research shows clear differences in the super-attenuating properties of S. cerevisiae var. diastaticus yeast strains and their potential for industrial brewing applications. Nineteen unknown spoilage yeast cultures were obtained as isolates and characterized using a broad spectrum of genetic and phenotypic methods. Results indicated that all isolates represent genetically different S. cerevisiae var. diastaticus strains except for strain TUM PI BA 124. Yeast strains were screened for their super-attenuating ability and sporulation. Even if the STA1 gene responsible for super-attenuation by encoding for the enzyme glucoamylase could be verified by real-time polymerase chain reaction, no correlation to the spoilage potential could be demonstrated. Seven strains were further characterized focusing on brewing and sensory properties according to the yeast characterization platform developed by Meier-Dörnberg. Yeast strain TUM 3-H-2 cannot metabolize dextrin and soluble starch and showed no spoilage potential or super-attenuating ability even when the strain belongs to the species S. cerevisiae var. diastaticus. Overall, the beer produced with S. cerevisiae var. diastaticus has a dry and winey body with noticeable phenolic off-flavors desirable in German wheat beers.

A re-evaluation of diastatic Saccharomyces cerevisiae strains and their role in brewing

“…Thanks to the glucoamylolytic activity of diastatic yeast, they have a competitive advantage compared with traditional brewing strains in dextrin-or starch-rich environments where concentrations of fermentable carbon sources are low. Beer is a prime example of such an environment, and most STA1+ strains, in contrast to ale or lager strains, are able to grow and produce carbon dioxide in fermented beer (Meier-Dörnberg et al 2018;Krogerus et al 2019). In addition to longer chain carbohydrates, Sta1p efficiently hydrolyzes maltotriose and other maltooligomers Kleinman et al 1988).…”

“…S2; Peter et al 2018). Media containing starch or maltodextrin as the only fermentable carbon source have also been developed (Meier-Dörnberg et al 2018;Burns et al 2020). Diastatic strains can grow on these media thanks to their glucoamylolytic activity.…”

“…Iodine can also be used to stain residual oligosaccharides in the growth media (Burns et al 2020). However, growth is typically very slow on starch-containing agar, often requiring several weeks, and plates should ideally be incubated anaerobically to reduce the amount of false positives (Meier-Dörnberg et al 2018). Durham tubes containing beer as growth media have also been used successfully to detect diastatic S. cerevisiae (Meier-Dörnberg et al 2018).…”

“…However, growth is typically very slow on starch-containing agar, often requiring several weeks, and plates should ideally be incubated anaerobically to reduce the amount of false positives (Meier-Dörnberg et al 2018). Durham tubes containing beer as growth media have also been used successfully to detect diastatic S. cerevisiae (Meier-Dörnberg et al 2018). For these, a sample of yeast is inoculated into sterilized beer inside a Durham tube, and carbon dioxide production is monitored by the buildup of gas in the inverted inner tube.…”

“…Hence, a combination of a growth-based and PCR-based method is therefore recommended to accurately differentiate spoilage and non-spoilage STA1+ strains at the expense of time. Realtime or quantitative PCR systems have also been developed for the detection of the STA1 gene, and the further advantage of these is that lower detection levels can be achieved and the level of contamination can also be quantified (Brandl 2006;Meier-Dörnberg et al 2018;Schönling et al 2019). To improve (i.e., decrease) the detection limit of these methods, a pre-enrichment in selective growth media can also be applied to the yeast sample.…”