A mechanism for molding food patties from a fibrous food product (e.g. poultry breasts, fish fillets, large pieces of pork muscle, etc.) uses a conventional mold plate positioned between a fill plate and a breather plate and cyclically movable between a fill position and a discharge position; the fill plate has fill ports, one for each mold cavity in the mold plate, through which the food product is pumped under pressure, each mold cavity having a substantially larger area than its associated fill port. Each fill port has a transitional rim, past which the food flows with an appreciable change in direction, that is smoothly rounded to avoid damage to the food fibers. Each fill port also has a cutting rim, past which a part of the filled mold cavity moves on its way to a discharge position; the cutting rim shears off any food fibers along part of one face of the patty. Preferably, the breather holes in the breather plate are confined to the periphery of each mold cavity position.