Sausages were originally made by stuffing a meat mixture into the intestines of a pig, sheep or other animal. When sausage manufacturers wanted a faster, more reliable way of making a high quantity of sausage - and when the material became widely available a half century ago - they switched to collagen.
A natural protein product, collagen comes from a layer of beef hide, removed and refined. The more refined the processing, the more tender the casing.
Collagen casing sausages are easy to cook, a good value and look great. Most important, they provide a tender bite and a fine "knack" - that familiar snap sound you expect when you bite into the perfect sausage.