Steryl anti-flor tablets consist of an inert pure-paraffin support in which allyl isosulphocyanate, a natural form of mustard oil has been dissolved. Mustard oil is a volatile substance with high antiseptic properties especially with regard to aerobic microorganisms. By floating on the surface of the liquid, Steryl tablets slowly release the allyl isosulphocyanate, which sterilises the air above it. As a result, the development of the film is inhibited together with other oxidation related bacterial and enzymatic surface alterations.