The use of Oxygen 18 in appraising the impact of oxidation process during beer storage

To appraise the incidence of oxygen in bottled beer, the stable nonradioactive oxygen isotope 18O2 was injected into the headspace just before ageing and subsequently analysed by proton bombardment and isotopic mass spectroscopy of all the most interesting beer fractions. Although oxygen did cause considerable oxidation of sulphites, polyphenols, and isohumulones, it was not incorporated into the carbonyl fraction, indicating that the cardboard flavour in beer is not due to lipid oxidation but to wort preparation. Nonenal potential measurement was found to be a good indicator of beer flavour staling. The impact of beer stabilisation treatments (addition of polyvinyl pyrolidone powder, potassium metabisulphite, ascorbic acid) was also investigated.