Method analysis of equilibrium-based oxygen determinations in packaged beer.

Kemper, E.A. and Patino, H.

Abstract
A computer program has been devised for use in calculating a equilibrium value for the headspace oxygen content of packaged beer. Measurements of headspace oxygen carried out using analytical devices such as the Hersch Cell Dissolved Oxygen Analyzer are corrected for temperature, pressure, ethanol content, ratio of liquid to vapour etc. Change in liquid to vapour ratio was found to be the most important variable and the error involved was assessed using the Monte Carlo Simulation technique and the Error Propagation Method. This error was proportional to the oxygen level being measured. In an example given the standard deviation was about 11% of the dissolved oxygen level i.e. there is a 33% chance that a can actually containing 1000 ppb will be measured as > 1110 ppb or < 890 ppb. By weighing canned beer the error can be reduced, in the example given from 11% to 4.4%. The effect on total oxygen content of removing a number of consecutive samples from a container can be calculated using the equation given. This is illustrated graphically for a beer with an initial oxygen concentration of 400 ppb where up to 5 samples of 0.5, 1.0, 2.0 and 4.0 ml are removed.
Keywords : analysis beer computer oxygen packaging