Yellow Grease Definition
Yellow grease is a category of fat that renderers built by collecting used cooking oils and restaurant greases and treating that material as a raw material.
How the category started
Fat collected from restaurants was traditionally of animal origin, tallow and lard. Frying media later shifted toward plant oils. The note records that this shift was made despite a lack of empirical data, and that most taste panels preferred foods cooked in animal fats. The shift changed the tallow and lard markets and produced a category sold as feed-grade animal fat or yellow grease.
How it is specified
Yellow grease is defined here as a fat product that does not meet the definitions for animal fat, vegetable fat or oil, hydrolyzed fat, or fat ester. Like any other grade of fat, it is sold on its specifications: the minimum percentage of total fatty acids, the maximum percentage of unsaponifiable matter, the maximum percentage of insoluble impurities, the maximum percentage of free fatty acids, and the amount of moisture. It also has to meet the Food and Drug Administration’s criteria for pesticides and other toxic chemicals. Those specifications are negotiated between buyer and seller on a contract.
Free fatty acids and feed use
Free fatty acids in fat were once read as a sign of rancidity, and questions remain about high-free-fatty-acid fat as a feeding ingredient. The research cited in this note does not treat free fatty acids, on their own, as a measure of fat quality. Park Waldroup and colleagues at the University of Arkansas (Waldroup et al., 1996) reported no difference in broiler performance when diets were supplemented with fats of low or high free-fatty-acid content, including a fat at 44.7 percent free fatty acids. Richard Zinn at the University of California (Zinn, 1988, 1989) reported similar findings in feedlot cattle. In the growth comparisons of fats at 10 percent and 50 percent free fatty acids, no difference was detected. A higher free-fatty-acid content, without rancid odor, a palatability problem, or a high peroxide value, did not change the feeding value in those studies. High free fatty acids can matter in industrial uses, including the esterification step used to make biodiesel.
Uses named in the source
Yellow grease is one of the fats and oils used as feeding fat. Industrial uses named here include biodiesel and burner fuel. The source line on this definition is H.W. Ockerman and Lopa Basu, Encyclopedia of Meat Sciences (Third Edition), 2024.
