Abstract
Saccharomyces cerevisiae sub-species diastaticus (S. diastaticus) is the main fungal cause of spoilage of carbonated fermented beverages in the brewing industry. Here, prevalence of S. diastaticus in nature and breweries was assessed as well as the spoilage capacity of its vegetative cells and spores. S. diastaticus could only be enriched from 1 out of 136 bark and soil samples from the Netherlands, being the first described natural isolate of this yeast outside South America. On the other hand, it was identified by PCR and selective enrichment in 25 and 21 out of 54 biofilm samples from beer filling halls in Asia, Africa, Europe and North America. ITS sequencing revealed that S. cerevisiae (including S. diastaticus) represented <0.05% of fungal DNA in 17 out of 20 samples, while it represented 0.1, 2 and 32% in samples VH6, VH1 and VH3 respectively. Next, vegetative cells and ascospores of the natural S. diastaticus isolate MB523 were inoculated in a variety of beer products containing 0.0–5.0% alcohol (v/v). Ascospores spoiled all beer products, while vegetative cells did not grow in Radler lemon 0.0, Radler lime mint 0.0 and Radler lemon lime 0.0. Notably, vegetative cells could spoil these Radlers when they first had been grown in alcohol free beer either or not mixed with Radler lemon lime 0.0. Conversely, vegetative cells that had been grown in Radler lemon lime lost their spoilage potential of this beer product when they had grown in YPD medium for more than 24 h. In addition, it was shown that cells grown in alcohol free beer were more heat resistant than cells grown in YPD (D52 40 min and ≤ 10.3 min, respectively). Together, these data show that S. diastaticus is a less prevalent variant of S. cerevisiae in nature, while it accumulates in breweries in mixed biofilms. Data also show that both vegetative cells and spores can spoil all tested beer products, the latter cell type irrespective of its environmental history.
Highlights
Several yeast genera can spoil beer but Saccharomyces cerevisiae subsp. diastaticus is the most dangerous spoilage yeast in breweries (Hutzler et al, 2012)
PALL PCR showed the presence of Candida and/or Pichia in all samples that were positive for S. diastaticus and/or S. cerevisiae, as well as in 5 other samples. 17% of the samples that were positive for S. diastaticus and/or S. cerevisiae was positive for Brettanomyces bruxellensis
21 S. diastaticus strains were isolated from 54 biofilm samples from 6 breweries located in Europe, Asia, North America and Africa
Summary
Several yeast genera can spoil beer but Saccharomyces cerevisiae subsp. diastaticus (in short S. diastaticus) is the most dangerous spoilage yeast in breweries (Hutzler et al, 2012). S. diastaticus produces phenolic off-flavor and causes haze formation and super-attenuation. The latter leads to increased alcohol content and over‐carbonation of beer (Andrews and Gilliland, 1952; Priest and Campbell, 2003). It is assumed that costs associated with spoilage incidences due to S. diastaticus contamination range from millions to billions of euros annually in Europe alone (Hut zler et al, 2012; Stratford, 2006). The reported incidence of S. diastaticus spoilage in the brewing industry has increased from 1 to 19 cases each year between 2008 and 2016 (Meier-Dornberg et al, 2017). S. diastaticus contamination had occurred during filling of the beer in about two-third of these cases, most likely originating from biofilms in the brewery (Timke et al, 2008). Cells in biofilms are known to have increased stress resistance (Quain and Storgards, 2009) and are not removed; some locations were recolonized in 2–12 h (Storgards et al, 2006)
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