Abstract: A container assembly for controlling rate of oxygen transfer from the atmosphere into a liquid stored in the container assembly having, a container with an oxygen permeability of 50 ml to 300 ml of oxygen per square meter of area of walls of the container for each millimeter of the thickness of the walls per 24 hour period at room temperature, a barrier member for providing a barrier to limit oxygen access from head space in the container to a surface of the liquid the barrier member having a construction which causes it to float on the liquid surface, and a peripheral flange surrounding the barrier member arranged so that it makes a slidable peripheral seal with the walls of the container.