Yellow grease is derived from used cooking oil from the fast-food industry. It is used to feed livestock, and to make soap, make-up, clothes, rubber, detergents, and bio-diesel fuel.
It is distinct from brown grease; yellow grease is typically used-frying oils from deep fryers, whereas brown grease is sourced from grease interceptors. Yellow grease can also refer to lower-quality grades of tallow (cow or sheep fat) from animal rendering plants.
Yellow grease is recovered, traded as a marginally valuable commodity, and has traditionally been used to spray on roads as dust control, or as animal feed additive, but has become a feedstock for biodiesel production.
The term has been in use for some time. A source from 1896 describes it as follows: “Yellow grease is made by packers. All the refuse materials of the packing houses go into the yellow grease tank, together with any hogs which may die on the packers’ hands.”