Carbon Dioxide Solubility in Beer

The amount of CO2 within a beer is a function of CO2 solubility, which in turn is affected by temperature, containing pressure, and beer composition. Historically, this variable was assessed through empirically derived pressure/temperature charts with the first appearing about 1939. Modern methods often involve empirical or semi-empirical formulas that yield close approximations to the aforementioned charts (at typical storage conditions). Other methods to determine CO2 solubility incorporate additional variables such as extract and alcohol content. Unfortunately, the origin of various pressure-temperature solubility charts contained in ASBC's Methods of Analysis or MBAA's Beer Packaging: A Manual for the Brewing and Beverage Industries, are largely unknown, as are the composition of the beers used to create these charts! This discrepancy results in potentially inaccurate CO2 values for differing beer compositions and is especially problematic when assessing modern methods that incorporate additional parameters. This paper attempts to contrast and compare modern and historical methods while considering the limited CO2 solubility reports in beer and sugar and ethanol solutions. In this paper, the accuracy of CO2 solubility charts and formulas are discussed while considering assumptions reported by the original authors. Finally, modern formulae are used with non-linear optimization techniques to generate the likely composition of the standard beer used to construct the original ASBC solubility chart. It appears that a standard beer of yesteryear is stronger than an average modern beer with an alcohol content of 4.22% (w/w) and a Real Extract of 5.78 degrees P.