Trays placed in an autoclave are coupled with microwaves from microwave generators
and move back and forth as they are processed to ensure even heating. The generators
are placed at the side of the autoclave so each generator connects to a wave guide
in the autoclave with upwardly directed decoupling openings immediately below the
tray to be heated. The distance between the decoupling opening and the tray is
maintained at less than one-half wavelength. The foods on the tray are heated first
from below and then the heat rises. When water in the lower food layers is heated,
steam forms and must pass through the cooler upper layers to escape. As it does
so, it loses heat to these layers, warming them and preventing scorching on the
food's surface as well as any bursting of the trays' seal.
