Or more basically what is diastaticus? A topic spoken about surreptitiously in brewing circles as if admitting to some embarrassing personal illness.

In fact, diastaticus is no hidden horror but an all too public one when your packages explode violently on opening, on shelves in a warm outlet or tragically in a customer’s hand. Gushing beer is embarrassing and hazardous and equally badly an indication of problems in a brewery’s microbiology.

There are two basic questions we should address at the outset. What exactly is diastaticus and where has it come from all of a sudden?

The first of these is microbiological. Simply put diastaticus is a yeast which can produce glucoamylase enzymes to digest dextrins in beer. This action releases sugars which can then be fermented. Now as we all know starch is digested in the mash to produce fermentable sugars and non-fermentable dextrins. Fermentable sugars are converted to ethanol and carbon dioxide in fermentation while dextrins remain inert to contribute to body and mouthfeel. The rule we typically work to is that dextrins can be safely left in a cask or bottle conditioned beer as they are not fermented by brewing yeasts Saccharomyces cerevisiae and S. pastorianus.

However, this is not universally true for other yeasts. In fact, most non-brewing or wild yeasts are well able to produce enzymes to digest larger sugars into fermentable ones which thus cause problems when carbon dioxide builds to unsafe levels. Any contamination with these yeasts in your beer will cause gushing.

Normally this should be limited to cask and bottle (or canned) conditioned beers as filtration and pasteurisation will remove yeast and thus the hazard. However, there remains the possibility of filtered or pasteurised beers being inoculated during packaging where contaminated environments in the filling area may introduce the yeast either from the environment or nearby biofilm.

Gushing thus suggests a contamination in beers with live yeast (although there are some cases where inert materials from malt may be the cause). A simple solution to diastaticus contamination is to maintain hygiene in the production of these beers particularly throughout fermentation and packaging. Naturally this would be standard practice but there is the complication where the yeast stock itself may be contaminated. In this case using a reliable yeast source is essential – ideally one with the facilities to check for purity. Looking in more depth to the problem it is relevant to note that diastaticus yeast is the normal condition and that brewing yeasts have been selected because they have a mutation in the STA glucoamylase gene rendering it inactive. This selection will have happened over centuries of use to provide the standard beers we generally brew today. However, recent surveys of yeast genomes show that many wild and some brewing yeast carry an active STA gene. This then answers our second question – why is diastaticus suddenly appearing? Aside from hygiene being less attentive during busy production new beer styles such as Saison and sours are using these very yeasts with active STA genes. While these provide the low attenuation associated with such beers once they are introduced to your production environments the possibility of contamination into standard beers is enhanced. These details are both worrying and reassuring. Worrying in that they enhance concern if you are using multiple yeast strains but reassuring in that they point to actions to minimise the hazard.

Hygiene is paramount to prevent cross contamination including not only local environmental cleanliness but also strict separation and management of yeast cultures from pitch to discard. For example, throwing a bucket of Saison yeast slurry into the central drain is sure to create an aerosol you don’t want to mix with your standard pitching. Segregating vessels and pipework for sole use by STA positive yeast is advisable as is double decontamination of any packaging system after use. Finally ensure that your yeast is from a tested source or checked by a competent laboratory.

Reassurance is important in order to be confident of your product’s safety but testing is not simple. Using starch or copper sulphate agar plates are one possible method but do not guarantee that all negatives are true. Alternatively forcing tests will give a predictive indication of problems if samples are kept warm at around 30oC. This though takes time. Molecular biology PCR techniques are more rapid and reliable as they are based on the gene sequence but require investment and laboratory skills.

Diastaticus may be viewed as a consequence of the innovations of contemporary brewing and a cost of diversifying beer portfolios. It is manageable but one further worry is the possibility of standard brewing yeasts incorporating the gene directly from the environment or mutating back to the active form. It is fortunate that we have the techniques to test this but is another indication that brewing is set to become even more technical in future years.

   Return to Brewlab blog

Acquire the skills and knowledge you need to succeed

From a one-day taster session to a nine-week intensive residential course. Whatever your brewing aspirations, Brewlab training is internationally recognised as one of the best ways to acquire the skills and knowledge you need.

Find your course