Diastaticus strains are found naturally as wild strains and are also sold by many culture banks for brewing, with identification of more confirmed species coming to light.

Yeast strains are classified as Saccharomyces cerevisiae var. diastaticus if they carry the STA1 gene. STA1 is the “signature” gene of diastaticus, meaning it will be found in all diastaticus strains. Genes are units of DNA that act as instructions and gene expression refers to how active a particular piece of DNA is. When a gene or sets of genes are present, they are not always being expressed, but it is possible for expression to occur due to a change in environmental conditions. When this happens to diastaticus, the yeast becomes capable of fermenting residual carbohydrates that are unfermentable to most Saccharomyces strains. This gene expression in turn can cause changes in taste, over-attenuation, and bottle bursting, among other consequence from a pitched strain or a single contaminant cell. The precise environmental conditions that influence diastaticus-specific gene expression have not been quantified.

A recent study in Europe investigated suspected diastaticus contaminations in breweries through the detection of the STA1 gene with PCR tests (Meier-Dӧrnberg, Jakob, Michel & Hutzler, 2017)1. It revealed that just 49% of suspected contaminations were diastaticus and only one involved a yeast supplier. Moreover, among the 52 breweries with one or more positive diastaticus contaminations, ninety-two percent of diastaticus contaminations came from within the breweries themselves. Further investigation showed that 71% of these cases came from the bottling/filling area and were traced back to contaminants in the filler environment and/or biofilms in the pipework system of the filler. Twenty-nine percent of cases came from the brewhouse, fermentation cellar, and storage cellar.

A list of commercially available Saccharomyces cerevisiae strains that are either confirmed or suspected to have the STA1 gene (i.e. STA1+) and are subsequently classified as Saccharomyces cerevisiae var. diastaticus. A caveat is that the presence of the STA1 gene does not confirm they are consistently expressing the extracellular glucoamylase. Further research is required (and is being performed in several labs), with greater attention paid to the expression of the enzyme.

Prepared by Joshua Mayers. Updated: 07-01-19 © 2018 by Craft Labs HB - Gothenburg, Sweden