Abstract The accurate determination of alcohol content and original gravity of beer is crucial to investigations of adulteration and substitution. Unfortunately, beer samples are unstable with respect to compositional change by evaporation and biological degradation. Recent guidelines recommend freezing suspect samples to preserve them. This technique was compared with other preservation techniques. Samples of live cask beer and pasteurised beer were stored at 4 °C, at 4 °C with the addition of salicylic acid, and frozen at −18 °C. They were analysed at intervals for their alcohol content and original gravity. It was found that the sample’s analytical integrity was maintained for 18 months by degassing and freezing in glass bottles.