FORMULATION AND TESTING OF CUPRIC SULPHATE MEDIUM FOR WILD YEAST DETECTION

Methods for detection and identification of beer-spoilage microbes

It is critical that breweries of all sizes routinely monitor the microbiome of their process to limit financial losses due to microbial contamination. Contamination by beer-spoiling microbes (BSMs) at any point during the brewing process may lead to significant losses for breweries if gone undetected and allowed to spread. Testing and detection of BSMs must be routine and rapid, and because even small breweries need the capability of BSM detection and identification, the method also needs to be affordable. Lactic acid bacteria (LAB) are responsible for most spoilage incidents, many of which have been shown to enter the viable but nonculturable (VBNC) state under conditions present in beer such as cold or oxidative stress. These bacteria are invisible to traditional methods of detection using selective media. This article describes several methods of BSM detection and identification that may be useful in the majority of craft breweries. While there are several genomic methods that meet some or many qualifications of being useful in craft breweries, real-time quantitative polymerase chain reaction (qPCR) currently best meets the desired method characteristics and holds the most utility in this industry, specifically SYBR Green qPCR. qPCR is a targeted method of detection and identification of microbes that is affordable, rapid, specific, sensitive, quantitative, and reliable, and when paired with valid DNA extraction techniques can be used to detect BSMs, including those in the VBNC state.

[Microbial contaminants in bottled craft beer of Andean Patagonia, Argentina]

The brewing activity in Andean Patagonia plays a very important role in the region's economy, being microbial contamination one of the main problems in terms of quality. The presence of contaminant bacteria and wild yeasts in beer generate microbiological, physical and chemical changes that impact on its sensory attributes. However, few breweries establish criteria and policies to guarantee the quality of their products in a microbiological sense. The purpose of this work was to study for the first time the incidence of microbial contaminants in bottled craft beers from Andean Patagonia, identify the main microorganisms involved and establish relationships between contamination and the physicochemical variables of beer. We analyzed 75 beers from 37 breweries from 12 different Patagonian cities. Our results showed that 69.3% of the analyzed beer exhibited contaminant microorganism growth. Bacteria Levilactobacillus brevis and wild yeasts of Saccharomyces were the main microorganisms responsible for these contaminations. In addition, we found that microbial contamination had an impact on beer sensory profile and also that pH was correlated with the presence of lactic acid bacteria in beer, being an indicator of contamination for these bacteria. In conclusion, we observed that 8 out of 10 breweries studied showed contamination problems, highlighting the need to design prevention and control strategies in microbreweries.

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

Abstract

Diastatic strains of Saccharomyces cerevisiae possess the unique ability to hydrolyze and ferment long-chain oligosaccharides like dextrin and starch. They have long been regarded as important spoilage microbes in beer, but recent studies have inspired a re-evaluation of the significance of the group. Rather than being merely wild-yeast contaminants, they are highly specialized, domesticated yeasts belonging to a major brewing yeast lineage. In fact, many diastatic strains have unknowingly been used as production strains for decades. These yeasts are used in the production of traditional beer styles, like saison, but also show potential for creation of new beers with novel chemical and physical properties. Herein, we review results of the most recent studies and provide a detailed account of the structure, regulation, and functional role of the glucoamylase-encoding STA1 gene in relation to brewing and other fermentation industries. The state of the art in detecting diastatic yeast in the brewery is also summarized. In summary, these latest results highlight that having diastatic S. cerevisiae in your brewery is not necessarily a bad thing.

Key Points

•Diastatic S. cerevisiae strains are important spoilage microbes in brewery fermentations.

•These strains belong to the ‘Beer 2’ or ‘Mosaic beer’ brewing yeast lineage.

•Diastatic strains have unknowingly been used as production strains in breweries.

•The STA1-encoded glucoamylase enables efficient maltotriose use.

Electronic supplementary material

The online version of this article (10.1007/s00253-020-10531-0) contains supplementary material, which is available to authorized users.

Identity, beer spoiling and biofilm forming potential of yeasts from beer bottling plant associated biofilms

Wild yeasts were isolated from process surfaces of two breweries. In total, 41 strains were obtained and differentiated by cultivation on CuSO(4) or crystal violet containing selective media, by fatty acid profiling and by a restriction analysis of the region spanning the internal transcribed spacers (ITS1 and ITS2) and the 5.8S rRNA gene. The restriction analysis showed the highest differentiating capacity and resulted in eleven groups. These groups were identified by the API ID 32 C kit or by sequencing the D1/D2 region of the 26S rRNA gene. Most of the wild yeasts were identified as Saccharomyces cerevisiae (46% of all isolates) and Candida pelliculosa (anamorph: Pichia anomala) (24%). No obvious differences were detected between the two breweries. While all of the S. cerevisiae isolates were able to grow in beer, only six out of 10 C. pelliculosa strains were able to tolerate this substrate. However, most of the C. pelliculosa strains showed biofilm formation in a microplate assay, but none of the S. cerevisiae isolates. Therefore, it is assumed that the former species is involved in attachment and primary biofilm formation on beer bottling plants, while S. cerevisiae is a late colonizer of a preformed biofilm but increased the beer spoiling potential of the biofilm.

Specific spoilage organisms in breweries and laboratory media for their detection

The Gram positive bacteria are generally regarded as the most hazardous beer spoilage organisms in modern breweries, especially the lactobacilli: L. brevis, L. lindneri, L. curvatus, L. casei, L. buchneri, L. coryneformis, L. plantarum, L. brevisimilis, L. malefermentans and L. parabuchneri and the pediococci: P damnosus, P. inopinatus and P. dextrinicus. Micrococcus kristinae is the only species within the micrococci relevant to brewing. The Gram negative strictly anaerobic bacteria are apparently increasing in importance and include Pectinatus cerevisiiphilus, Pectinatus frisingensis and Selenomonas lacticifex, reported as obligate beer spoilage organisms: Zymophilus raffinosivorans as a potential beer spoilage organism; Megasphaera cerevisiae as an obligate spoilage organism of low alcohol beer and Zymomonas mobilis as capable of spoiling primed beer. With improved process technology the importance of aerobic bacteria has decreased and the same applies for the Gram negative aerobic bacteria Hafnia protea and Enterobacter cloacae which are capable of surviving beer fermentation. Beer spoilage organisms include several so-called wild yeasts, of which Saccharomyces species are generally considered the most important. Even though the detection of beer spoilage organisms by cultivation in laboratory media does not always provide the specificity and the sensitivity required, the use of selective media and incubation conditions still appears to be the method preferred by breweries. The media used depend on the type of sample, the specificity required and, for detection of wild yeasts, to some extent, the characteristics of the culture yeast. Among the media reported so far no single medium can be used to detect all members within a group of specific beer spoilage organisms and further work on the development of improved substrates are required both for bacteria and wild yeasts.

Flow cytometric detection of wild yeast in lager breweries

A flow cytometric method for detection of wild yeast infections in breweries is reported. It is based on selective enrichment in Malt extract Yeast extract Glucose Peptone broth (MYGP) at 37 degrees C and in MYGP with 200 ppm CuSO4 at 25 degrees C, staining with a fluorochrome precursor and flow cytometry. In experiments with several types of wild yeast isolated from breweries and two different strains of lager yeast it has been possible to detect one wild yeast per 10(6) culture yeast after 48-72 h of incubation and, in some cases, after 24 h.