Method of treating closure for food or beverage, typically treated cork

In a first aspect, the present invention provides a method for producing a coating or diffusion layer on a substrate (e.g. a cork) for use in contact with a food product or beverage, said coating or diffusion layer preventing or inhibiting passage through (e.g. from a cork to an alcoholic beverage) of flavour-active or odour-active compounds (commonly known as cork taint), and said method comprising applying to the surface of said substrate an effective amount of a reactive polymer, said reactive polymer being a polymeric material comprising first functional groups which react with at least one flavour-active or odour-active taint compound and second functional groups (which may be the same as or different from said first functional groups) which react with said substrate. In a second aspect, the present invention provides a coated substrate, and in particular a coated natural or synthetic cork, produced according to that method.