The gold foil bag the smoked salmon is placed in is called a retort. Think of a retort as a "soft can." A retort provides all of the protection of a can while allowing the salmon to be left in a fillet form. Once the salmon is placed in the bag it is sealed and  placed in a pressure cooker and "flash canned" so quickly that none of the delicious flavor or moist texture is lost. Now that the smoked salmon is "canned in the bag" it needs no refrigeration and has a three-year shelf life.