I found on Wikipedia that it is made from animals' skin and bones. The article describes the steps of gelatin production from a technical perspective:
The manufacturing processes of gelatin consists of three main stages:
- Pretreatments to make the raw materials ready for the main extraction step and to remove impurities which may have negative effects on physiochemical properties of the final gelatin product,
- The main extraction step, which is usually done with hot water or dilute acid solutions as a multi-stage extraction to hydrolyze collagen into gelatin, and finally,
- The refining and recovering treatments including filtration, clarification, evaporation, sterilization, drying, rutting, grinding, and sifting to remove the water from the gelatin solution, to blend the gelatin extracted, and to obtain dried, blended and ground final product.
How can you make gelatin from scratch in your own kitchen?