Solving the puzzle of an off-spec "musty" taste in canned beer... a partnership approach.

Anderson, S.D., Hastings, D., Rossmore, K. and Bland, J.L.

Abstract
In 1991, one of the Stroh Brewery Company's breweries began to experience a recurring problem of "musty" off flavour in canned beer. As chemical analysis of the rejected product failed to identify the substance responsible, an investigation team of quality assurance staff was set up. Since only canned beer was affected by the problem, the canning line was the main focus of attention. It was found that the off flavour usually appeared in beer canned during the first half hour after starting the canning line (including restarts after any stoppage lasting more than about ten minutes). Because the layout of the canning line concerned was such that the empty can conveyor passed over the pasteurizer, the possibility of contamination from that source was experimentally investigated. It was found that cans suspended over the pasteurizer or placed near the filling machine for ten minutes or more, as well as those placed in other areas of the brewery where ventilation and hygiene were poor, before filling and pasteurization were found to be affected when the beer was tasted. Moreover, cans from one of the two manufacturers supplying the brewery were more frequently and more severely affected than those from the other, despite the absence of identifiable differences between them. Microbiological analysis of water from the pasteurizers and air from their immediate vicinity revealed a wide variety of microorganisms, including several species of mould fungi (members of genera such as Geotrichum, Penicillium and Cladosporium) capable of producing odours similar to the off flavour in the beer. Further tests indicated the likely identity of the compounds responsible. To control the problem, stainless steel covers were fitted both to the pasteurizers and to the empty can conveyors and rinsers so as to reduce the risk of contamination being carried in pasteurizer water vapour, the disinfection of the pasteurizers was intensified, a biocidal conveyor lubricant replaced the product previously used and the ventilation of the canning hall was improved. A further outbreak of the problem was traced to the floor drains near the canning line and was dealt with by commencing a daily disinfection of the floors and drains in the packaging hall. As a further precaution, the supply of empty cans to the line was cut off shortly before each scheduled shutdown, ensuring that all cans already on the line would be filled immediately and not left empty on the conveyor. Further hygienic improvements, including the replacement of the concrete ceiling of the packaging hall by a plastic coated metal one, were under way at the time of writing.
Keywords : beer can canning line contamination mould off flavour pasteuriser vapour water