The majority of Ossett's casks are stainless steel, but they do have a batch of plastic ones. The plastic casks currently produced do have critical reinforcement around stress points. They also enable a brewery to use its distinctive colours for identification and recovery of stray casks, as well as there being a substantial cost saving if casks go missing . Cask exteriors are given a pre-wash on a machine in the brewery yard before the triple cask washer flushes the interiors.