Shielding system for protecting select portions of a food product during processing in a conveyorized microwave oven

A conveyorized microwave oven incorporates a shielding system mounted within an oven cavity of the microwave oven. The shielding system is provided to prevent select portions of a food item traveling through the microwave oven from overheating relative to the remainder of the food item. The present invention is particularly adapted for use in connection with the tempering, cooking or thawing of parallelepiped or rectangular-shaped food items and includes a frame structure fixedly mounted within and traversing substantially the entire length of the oven cavity, with the frame structure having a generally rectangular cross-section defined by both microwave impermeable portions and microwave transmissive portions on each side.