Saccharomyces cerevisiae var. diastaticus
Saccharomyces cerevisiae var. diastaticus is a widely known contaminant in the brewing industry that can have devastating effects on product. The primary issues it causes are off-flavors and super-attenuation. Due to detection limitations, a contamination of this type can be immensely harmful. Diastaticus causes refermentation in the package by continuing to breakdown longer chain sugars that were left untouched by the primary yeast. This means that it can cause major problems for packaged product months after it has already left the brewhouse.
Diastaticus’ mode of action for breaking down longer chain sugars lies in its ability to produce and excrete an enzyme called glucoamylase (Yamauchi, Yamamoto, Shibano, Amaya, & Saeki, 1998). This enzyme is encoded for by three homologous genes, STA1/2/3. In addition to these genes the upstream promoter region plays an important role in regulating them. Until now the main detection for diastaticus has simply been the presence or absence of the STA genes (Meier-Dörnberg, Kory, Jacob, Michel, & Hutzler, 2018). However, it has been found that many strains may contain the STA genes but do not exhibit degradation of longer chain sugars. This is due to a 1162 base pair deletion in the promoter region. This promoter region is crucial for expression of these genes and when it is not functioning properly the yeast does not exhibit a high degree of diastatic ability. Work is being done to include this base pair deletion in molecular detection methods and will give a better understanding as to which strains are truly diastatic (Krogerus, Magalhães, Kuivanen, & Gibson, 2019).
Current molecular detection methods available on the market do not take this base pair deletion into account. So, while the current molecular method of testing for diastaticus is useful, it does not give a correct identification of diastaticus. This can be both helpful and harmful. It can tell you an organism is in your beer that should not be there but may also raise a false alarm as to the severity of the contamination. Another false assumption when utilizing molecular based methods is characterizing a positive as a living organism. While there is no currently available molecular method on the market for differentiation of live vs. dead organisms, there is extensive research being done.
For any consultation regarding a possible diastaticus contamination please contact BSI through our technical support line, 719-482-4895 ext. 3, or send in a sample by following the directions listed on our website at https://brewingscience.com/contamination-testing/
-Blog by Kory Davis – QC & Propagation Specialist
Meier-Dörnberg, Tim, et al. “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.” FEMS Yeast Research, vol. 18, no. 4, 2018, doi:10.1093/femsyr/foy023.
Krogerus, K., Magalhães, F., Kuivanen, J., & Gibson, B. (2019). A deletion in the STA1 promoter determines maltotriose and starch utilization in STA1 Saccharomyces cerevisiae strains. Applied Microbiology and Biotechnology, 103(18), 7597–7615. doi: 10.1007/s00253-019-10021-y\
Yamauchi, H., Yamamoto, H., Shibano, Y., Amaya, N., & Saeki, T. (1998). Rapid Methods for Detecting Saccharomyces Diastaticus, a Beer Spoilage Yeast, Using the Polymerase Chain Reaction. Journal of the American Society of Brewing Chemists, 56(2), 58–63. doi: 10.1094/asbcj-56-0058