Written by Siren

Midnight Merriment - Product Recall


Thank you to everyone that has received, shared and responded to our notice. We have been able to credit around 50 people and will continue to offer the same compensation going forward. Please see the post below for full details. 

For now, we would like to update you all on our extensive investigations, the findings that have resulted and the improvements we are able to implement as a result. 

The first signs of contamination occurred 4 months after packaging, which made the investigation difficult, so we really had to think outside our normal avenues to get accurate information. We know now that it was Saccharomyces cerevisiae var. diastaticus (S Diastaticus) that caused the issue. 

S. Diastaticus

So what is S. Diastaticus? It is a member of the same species as standard brewers yeast, with an inherent gene that produces a glucoamylase enzyme. This is the same gene present naturally in many saison yeasts, which ultimately produces 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'. They are then 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 packaged and shipped. 

Testing and QC

Tests for Diastaticus are available and they are and were part of our routine for all beer QC. However, the levels involved in Midnight Merriment were too low for us to detect. Working with the help of external labs, we have been able to retrospectively find this problem. 

Our lab now contains a sterile filtration system for micro plating, which increases our threshold of detection of microorganisms by more than 200 times. This means we can sample a bigger volume of beer, which gives us a more accurate reading of microorganisms in our process, if any exist. Frustratingly, this system was on order at the time of the issues we faced, but it is now up and running. 

The external labs also used different methods of detecting contaminations, which helped us in finding the Diastaticus in this beer. This too has allowed us to improve our current processes, as we adopt new techniques to increase our range of testing. 

We have developed a tool for helping us investigate quality issues, which will allow us to investigate faster and capture all the information in a more efficient way. This was our first recall investigation and we learnt a lot from the process. 

As part of the investigation, we reviewed the entire process and found improvements to our sampling, process, hygiene and methods. Even if they were not a root cause in this batch, we have found improvements to prevent future issues occurring, which is very valuable. 
Finally, we have put in place internal audits to review batches of beer using the tools and methods mentioned above.

We will continue in our determination to keep improving and refining all of our quality systems and processes. 
Once again, we would like to apologise for this situation and the inconvenience and disruption it has caused. As always, we’ll continue to be as transparent and upfront as possible, while doing everything we can to rebuild your trust.

Thanks from all the team at Siren. 



It is with regret that we write today to advertise an official recall of MIDNIGHT MERRIMENT 330ml cans.

Key Points 

  • We are immediately recalling 330ml cans of Midnight Merriment

  • The beer was released in December and therefore we expect the majority will have been consumed. Please note that if you’ve already drunk the beer, it was entirely safe. The issue is around pressure build up in the cans, as opposed to any kind of health risk. 

  • We are communicating information on how to safely dispose of the beer cans 

  • There is compensation available, read on for details depending on how and where you purchased the beer 

  • We have included some information regarding our investigations so far, with updates to follow 

  • Read on for more information  


We have now received a few reports of Midnight Merriment cans bursting within the last 2 weeks. We have since instigated a comprehensive quality investigation into the product.  

We have been testing a range of our archive cans from different dates and times in the canning runs, and although we have been unable to confirm a refermentation issue in our retention cans, the photos we have received suggest that it’s a result of excessive pressure building up in the cans, which is in turn likely the result of refermentation in can. 
We’re continuing to force-age cans in an incubator in attempt to recreate the issue. However, given the nature of the images we have seen, we have taken the decision to recall all cans. 


Quality control is incredibly important to us. Last year alone we invested approximately £20,000 in a new laboratory and equipment, as part of a continued philosophy that quality should always take priority above growth. We have a highly skilled team member full time in our lab, and in addition to that, we work with external partners to corroborate results and provide us with additional insight, an ongoing investment of more than £10,000 / month. 

Of course, this only makes it more heartbreaking to witness issues like this with our cans. It’s the first time we have experienced such an issue and we will be doing everything in our power to ensure it’s the last. 

Our investigations so far include, but are not limited to, the following: 

  • We have re-run all of our standard tests to see if anything differs from original results, with no discrepancies. 
  • We have investigated possible over-attenuation caused by Diastaticus gene using in-house PCR and our standard method. Sample have been sent to external labs for further testing and we’re running various different enrichment methods. 
  • We have sent further samples to an external lab to be analysed using a different PCR system, which can identify a wider range of organisms than ours. 
  • We are running numerous stability tests from various times in the canning runs at different temperatures in incubators, in a ‘forced-ageing’ process at a temperature optimised for the yeast. 
  • We have a correlation now of a few reported problem cans within a short period of time, so we are using that timing as a focus for investigation. 


  • We are investigating the combination of yeast used to ferment this beer. We co-pitched two strains within the same attenuation limits, however one of the two strains was not something we had used before in a combination. Although it was thoroughly vetted before use, it was a different strain to our house yeast and it cannot be ruled out yet as a possible cause. 
  • We’re investigating all ingredients used, in particular anything added post-fermentation. This includes consultation with our suppliers. 


  • We have investigated the possibility of seaming issues, but concluded the build up of pressure would not have been possible had this been the case.
  • We have investigated the structural integrity of the cans used across these batches and have ruled it out as a potential cause. 

In short, we will leave no stone unturned to analyse what has happened here, what we could and should have done differently and what new processes we can implement to prevent it from ever happening again. 

Nitrogen Cans 

Cans that are nitrogenated are under higher pressure than those that are carbonated, typically a range of 35psi in comparison to an average of 15psi. This is not any cause for concern in itself, although it does mean that there is less margin for error in any case of refermentation, however slight it may be. This is also why nitro cans are firmer to the touch in general. 

The cans we use are rated to 90psi, so our nitro beers are well within spec. Please rest assured that we have not experienced any issues with any of our other Nitro beers, and they are completely safe to buy and enjoy. 

What Happens Next 

If you have already consumed the beer: 

We hope you enjoyed it, and let us just reiterate that you have nothing to worry about, the beer itself was entirely safe and good to drink. 

If you have can(s) of Midnight Merriment stored in your fridge: 

We have no reason to believe that there will be any concern of refermentation if the beer has been stored in a fridge since receipt. We have been unable thus far to recreate the issue with archive cans stored cold or ambient, but we know that there are examples of over-pressurised cans that were stored ambient in homes. If you would rather not drink the beer, please move onto the next section. 

If you have can(s) of Midnight Merriment stored ambient: 

We are advising that you dispose of the cans, as opposed to attempting to return them to us, or drinking them. We recommend the following procedure, opening the can while submerged underwater: 

  1. Run water into a sink of bucket, use enough cold tap water to be able to fully submerge the can on its side. 
  2. Rotate the can so you have access to the tab to open the can. 
  3. Open the can underwater facing away from you. 
  4. Once the can is open and the pressure has stabilized you can empty the can into the sink/container and then drain. 
  5. Please take a photo of the bottom of the can, showing the best before and canned-on dates.
  6. Prepare to send the photo to us, more details to follow. 

Here is a video showing the full process:  

We of course understand that this is not what you expect from us as a brewery. We would appreciate the opportunity to make things right with everyone who has been caused inconvenience and disappointment. 

If you purchased the beer from our webshop, we have two options: 

  1. We will offer you twice the retail value of each can in online credit, along with free delivery. This can be used towards anything you like from the webshop with no minimum order required, on us. We always advise making the most of the shipping services, but ultimately, it’s up to you. 
  2. We will offer a full refund for any cans you have to dispose of. 

Email [email protected] with your preferred option and we will process each case as quickly as possible. Please remember to attach a photo of the base of your can to this email.

Beer52 Customers 

A significant quantity of this beer went out to Beer52 subscribers. We will offer exactly the same compensation as above, please follow the same procedures listed. 

Learning and Improving 

We are sincerely very sorry that this has happened. It seems as though it’s a very limited issue, but that offers us no consolation. One dangerous can is one dangerous can too many. We will learn and improve from this mistake, and be forensic in our work to ensure it is never repeated. If you have this beer at home, please take us up on the offer to compensate you. Although we understand it will take time to rebuild the trust in our products, earned over many years, we would love to start that process right now. 

Thank you for your continued support.