Dairy cows feed in California

More than meat ... humans are only willing to eat 51 per cent of a cow or bull's body, leaving behind millions of tonnes of hide, hair, hoofs, horns, bones, blood and glands to deal with. Photo: Reuters

WHEN a cow tested positive for mad cow disease in America for the first time since 2006 last week, officials were quick to assure the public its meat was never going to enter the human food supply.

But if you're not going to eat a dead cow's meat, what are you supposed to do with it?

Make pet food, floor wax and explosives, among many other things. A large portion of the liquid fats are sold to refineries that reduce them into chemicals to make crayons, shaving cream, detergent and a long list of other products.

Glycerin, one of the many chemicals derived from cow fat, is an ingredient in dynamite. In recent years, rendered cow fat has been increasingly used to make commercial biofuels, and researchers are experimenting with adding animal byproducts to concrete and plastics.

Americans produce an astonishing quantity of cow leftovers.

Humans are only willing to eat 51 per cent of a cow or bull's body, leaving behind millions of tonnes of hide, hair, hoofs, horns, bones, blood and glands to deal with.

Leftover cow parts such as hooves and hair are not worth very much in their whole form, so renderers grind them into a paste or powder and load that into a cooking vessel at a steady rate using heat, pressure, and steam to break the material down.

The renderer might add other, non-animal waste products into the cauldron, such as used vegetable oil.

About half of the paste is water, which evaporates during this process. The lumpy soup that emerges from the end of the cooker is separated into liquid fats and solid proteins, using either a centrifuge or press.

While many people find the process foul, and some worry about the industry's safety, renderers argue that their processes provide a use for what would otherwise be an enormous amount of waste.

The Slate