A note on ethyl acetate formation in canned ‘draught’ beer

Abstract

Beer canned in packs of 16 oz or less is carbonated up to 2.7 volumes and pasteurized in the sealed can.In recent years beer canning has been developed in Great Britain to include the packing of 'draught' beer (which is under 1 -6 volumes of carbon dioxide) in 4 and 7 pint open-top cans. A few packers are producing a sterile filtered beer aseptically filled into 4 pint cans which are hermetically sealed with standard can ends. However, for most canned 'draught' beer aseptic techniques are not followed, and, since the product is not pasteurized 'in can', only a limited shelf life is expected. This beer is filled into 4 and 7 pint cans fitted with either one or two rubber stoppers inserted in one end by means of which headspace pressure is controlled. One of the rubber stoppers is normally pierced to act as a valve allowing the can to vent at a predetermined pressure. After purchase the beer may be dispensed through one of the bung holes by removing the stoppers.Spoilage of this draught beer, characterized by a strong ethyl acetate-like odour, in occasional cans fitted with rubber stoppers, has come to our attention. One such can showed the presence of approximately 1% of ethyl acetate, confirmed by gas chromatography. A thick deposit was present in the can. Large numbers of yeasts and small rods were seen on microscopic examination and a number of strains of yeasts and acetobacter type bacteria were recovered in cultures. Among the yeasts isolated was a species of Hansmula and, using the Lodder & Kreger-van Rij (1952) classification, this was considered to be a strain of Hansenula anomala. All the various organisms isolated, when inoculated into similar 4 pint cans of normally carbonated beer (approximately 1.5 volumes), showed no obvious development and failed to reproduce the 'spoiled' condition even after protracted incubation at room temperature.