Wild yeasts usually grow together with brewer’s yeasts. Their names are Brettanomyces, Pichia, Candida, Hansenula, Saccharomyces cerevisiae var. diastaticus… Especially the super attenuating members of the wild yeasts mostly come in low numbers, so they stay undetected during the production process. Only after brewer’s yeast has done its job – fermenting most of the available sugars – the time for wild yeasts has come: Some yeasts as S. diastaticus further break down the more complex carbohydrates like starches and dextrins by extracellular glucoamylase enzymes, starting a secondary fermentation. When super attenuating yeasts contaminate beer, they can take long time until they start growing, often weeks or even months after bottling. However, once a secondary fermentation is starting in finished beer, the results can be not only off-flavors, haze and often a raise of the alcohol content exceeding governmental regulations, but even more dangerously a considerable pressure formation in the packages due to over carbonation. Concerning these risks, the detection of wild yeasts in beer will usually always lead to a complete recall of all contaminated beer from the market.
The strain description of Saccharomyces cerevisiae var. diastaticus gives the following information: This yeast is facultative anaerobic, can ferment typical sugars similar to Saccharomyces cerevisiae plus starches and dextrins. Its morphology is comparable to the bottom fermenting brewer’s yeast Saccharomyces pastorianus, cells are oval to egg-shaped, mostly single or in pairs. S. diastaticus suspended in water can survive 10 min at 59.5°C, but all cells die when exposed to 60.5°C for 10 min. This is about 8°C higher than culture yeast or many other wild yeasts can survive at similar conditions. Fermenting wort with O.G. 1073 S. cerevisiae var. diastaticus can lead to a limit of attenuation of 1004, which is equivalent to 1°p (ref. 1).
When you face a contamination with S. diastaticus, conventional analysis by microscopy will probably not detect it during the production process, as this wild yeast looks just as your brewer’s yeast. To test for S. cerevisiae var. diastaticus, we are recommending a combination of the following methods covering enrichment, sensory and PCR:
Once you detect growth of wild yeast, you need to collect more information as it helps you not only to find and eliminate the contamination source, but – even more important – prevent the following brews from spoilage!
Wild yeast detection generally can take a long time as these species might grow slowly, but never underestimate their hazard potential!
Include wild yeast testing into your routine quality control!
Take this challenge, especially when also producing sour beers!
References / More information:
We are fast and competent in doing routine analyses as enrichments, determination of colony counts and the differentiation of microorganisms – service and quality are most important for us. Of course we respond to your requirements and always deliver prompt and reliable results – if necessary, even through weekends.
Spoilt product or positive enrichments are further discriminated – fast and specific by PCR analyses the same day as the samples are received. We further identify unknown bacteria, yeasts or molds from product or the production area within 3 to 5 days by DNA sequencing.
Our work does not end at the analysis result, we further advise you how to deal with a contamination and propose the next steps to minimize the risk for further batches in your production line. You can also count on us when optimizing your routine quality control measures.
PIKA FastOrange is a nutrient medium which was developed especially for the detection of beer spoiling microorganisms in beer and through the whole production process. Following the one-for-all principle, it can be used for enrichment of all brewery samples.
PIKA Detection Kits B were developed for routine control of products and the process line. With Screening Kits, groups of different bacteria which can spoil a product are specifically targeted together. And so even the costs stay within limits.
Developed for use in a production laboratory: Optimised for the extraction of genomic DNA from beer, wine and other beverages as well as from malt, grain and cereals – for the detection of bacteria, yeasts and molds. Cost saving thanks to simple and fast handling and a minimum of equipment needs.