cap 10 is attached to the bottle 12 the cap 10 is attached such that there is initially an air tight seal between the membrane 18 and the rim 34 of the bottle 12 the flexible membrane 18 is initially in a flaccid state as shown at 23 in phantom in fig2 as the heated product cools a vacuum is created inside the bottle and the flexible membrane 18 is sucked into the bottle it will be appreciated by those skilled in the art that it is only when the cap is first attached to the bottle that it is important to achieve an air tight seal between the flexible membrane 18 and the rim of the bottle thereafter once the cap has been opened the quality of the seal is less important once the cap is removed from the bottle since the flexible membrane 18 is attached to the cap it is removed with the cap as shown in fig1 a it will be appreciated by those skilled in the art that this is a clear advantage over the prior art that has a seal attached to the rim of the bottle such a prior art seal can often be very difficult to remove as well these prior art seals are relatively unsightly and by moving the seal into the cap this consumer unfriendly appearance is reduced since the flexible membrane is attached to the cap rather than the bottle it is further distanced from.