a process and apparatus for the commercial sterilization of thin - walled , high - profile plastic containers , which are hermetically sealed with an easy - peel aluminum foil / plastic - coated lid stock material . the apparatus is a rack of molds , each mold having a recessed groove to support the lip of the plastic container and a mold lid having a rigid portion covering the lid and a resilient portion inside the rigid portion to permit the lid of the plastic container to expand in a controlled manner during sterilization . the rigid portion of the mold lid can be angled to fit the contour of the expanded container lid .