Gelatin from Bones and Skins

Gelatin is collagen broken down by hydrolysis. Most is made from by-products of the meat and leather trades: pork skins, pork and cattle bones, and split cattle hides. The same thing happens at home when cartilaginous cuts or bones are boiled and the cooled stock sets to a jelly. Commercially the raw material is cleaned, the collagen is hydrolysed with acid (type A gelatin, suited to pig skin, 10–48 hours) or alkali (type B, suited to cattle hide, several weeks), the gelatin is extracted in hot water in several stages, and the solution is filtered, evaporated, dried, ground and sifted at the lowest temperatures possible to keep its gel strength.