Popular belief has it that gelatin comes from horses' and cows' hooves. Kraft, the maker of JELL-O, asserts that hooves do not contain the necessary collagen and therefore are not used in the production of their JELL-O brand gelatin product.
The production of gelatin starts with the boiling of bones, skins, and hides (not hooves) of cows and pigs, a process that releases the protein-rich collagen from animal tissues. The collagen is boiled and filtered numerous times, dried, and ground to a powder. Because the collagen is processed extensively, the final product is not categorized as a meat or animal product by the federal government. Very strict vegetarians avoid gelatin entirely, but more permissive vegetarians have no problem including JELL-O in their diets.