We recently had a customer who had a cider product that was in kegs and was giving a hotel customer some issues. The keg in question was foaming so much that the publican could not use the product at all and returned the keg to the maker. There were a number of kegs in the batch and so several more were checked. One nicely shot a stream of cider over 10 meters!
The customer had been packaging their product in kegs for some time and had never had this issue before so wasn’t sure what was causing the problem. The packaging was done at a third party bottling company a few months prior to the incident.
The cider was produced in the standard way which included sweetening the product after fermentation was completed. The cider was cross flow filtered at 0.2 µm and then sent to the bottling line in bulk plastic containers. At the bottling plant it was kept at 2 oC then placed in carbonation tanks and carbonated and then put into kegs at the bottling plant. The kegs were then shipped back to the maker’s premises and stored in a non-temperature-controlled area.
Upon discussion with the client it was decided that a full sterility check would be completed initially to see if any microbiological activity was occurring that could have given rise to the extra gas and foaming. The growth on the agar plate very quickly grew a lovely, large and healthy crop of Saccharomyces yeast!
As the cider had been sterile filtered prior to shipping to the bottling plant it appears that either the filtration was faulty or some yeast contamination occurred post filtration.
However, this particular maker has discovered the lesson that Saccharomyces, whilst being a friend of those doing alcoholic fermentations, does not always behave well and can also end up being a false friend and doing a lot of damage. Sterility control post-fermentation is obviously a critical control issue.