A mould-form fryer uses a top conveyor to transport snack pieces through a constant velocity oil stream without needing a bottom mating conveyor. The fryer housing controls the frying atmosphere, and uncooked snack pieces enter the fryer on a bottom conveyor. A steam shield separates the front-end vestibule from the downstream fryer housing, and manifolds introduce inert gas into the front-end vestibule, thereby providing a sufficiently low-oxygen and condensable gas or steam environment near the product’s submerging point.