Sausage Casings are the “skin” of the sausage, giving it its shape, appearance, and consistency as well as affecting its shelf life. Natural animal casing were the first casings, made from the sub-mucosa, a layer of the animal intestine that consists mainly of collagen. According to recorded history of man and civilization, for as long as man has been carnivorous, the intestinal tract of meat animals have been used for sausage casings.