Abstract: In a pressure vessel of the type used for processing a product with a liquid cryogen such as the impregnation of tobacco with liquid carbon dioxide for expansion thereof, a withdrawal door, pivotally hinged to open to permit gravitational discharge of the processed product, includes a grating to support the product in the vessel when the door is closed. A wire screen mesh is disposed on the grating to permit gaseous and liquid cryogen to pass therethrough while substantially preventing product from passing therethrough. A holding apparatus includes means for securely holding the screen fixed relative to the grating at the periphery and interior surface portions of the screen, the apparatus preferably including a gridded structure for minimizing stretching and tearing of the screen during discharge of the processed product from the vessel.