Affogato is a beer we produced back in May for our Project Barista series. Recently, one of our customers very kindly informed us that they had a highly carbonated bottle that did not taste as they were expecting.

We have carried out our own analysis on our library stock and found that the beer has refermented in the package due to an organism called Saccharomyces cerevisiae var. diastaticus (S Diastaticus).

We set very high standards for our QC at Siren and take it very seriously. Every brew is sampled at 5 individual points during the fermentation process and sent off to an independent and specialist lab. Then prior to packaging beer we also run a very sensitive in-house DNA test, targeting specific spoilage bacteria and brettanomyces. This beer passed all the tests available to us at that time.

So what is S. Diastaticus? It is a member of the same species as standard brewers yeast that produces a glucoamylase enzyme; the same sort of enzymes we use in a Brut IPA or are present naturally in many saison yeasts which produce super dry beers. Diastaticus contamination can result from a very small number of cells, potentially as few as a single cell, which can go undetected in all of the usual tests that a brewery would carry out. These few cells are out-competed by the normal brewing yeast, numbering millions of cells per milliliter, until the beer is 'finished' and they are able to eat and grow using the remaining complex sugars and polysaccharides that our brewing yeast cannot, therefore contamination can only become apparent some weeks or months after a finished beer has been bottled and shipped.

Indeed it is only in the last 3 months that our PCR DNA equipment has had a test screen available to use to identify any potential contaminations. Because of the many issues that were being publicised at the time, naturally we implemented it straight away, and know that none of the beers we have put out since we had the test available had any presence of Diastaticus.

Unfortunately Affogato was produced before this test was available to us. This beer was the first prop of a new yeast and at this stage it looks like that is how the contamination came into our brewery. We are conducting further tests on beers produced around the same time to ensure that this is an isolated incident

Our immediate concern is that Affogato was a beer that had a very high finishing content of sugar left in the beer, a lot to carry on being converted to CO2, so we need to ask anyone who has one in their cupboards, cellars or fridges (although our library stock in our cold room have shown no sign of refermentation), to contact us immediately. We will then respond with what to do, and how we can compensate you.

If you would like to know more about this issue, there are a few links below that show the work currently being done in this field:

https://discussions.probrewer.com/showthread.php?69995-Refermentation-in-Packaged-beer-due-to-Diastaticus

https://precisionfermentation.com/2018/07/23/diastaticus-infected-beer-wolf-in-sheeps-clothing/

https://www.goodbeerhunting.com/sightlines/2017/12/11/its-fairly-widespread-yeast-contamination-in-the-wake-of-left-hands-lawsuit

Thanks for your continued support.

Darron Anley, Founder.