Slices and blocks of cheese were coloured with aqueous methylene blue solution and vacuum-packed or wrapped in the films to be compared. The extent of bleaching of the dye after 14 days gave a good indication of the extent to which oxygen was excluded by the film. Similar results were obtained with vacuum-packed slices and with wrapped rindless cheeses.

With polythene-coated and wax-coated MSAT cellophane films there was little or no reduction of methylene blue on the cheese surface. Similar films, including a lamination of foil or MXXT cellophane, allowed complete or almost complete bleaching.