In some industry discussions, the word grease may refer to yellow grease, choice white grease, or combination’s of fat and oil products.


A reference to grease by the general population may refer to yellow grease, choice white grease, edible or inedible tallow, lard, trap grease, poultry fat, hydrogenated vegetable oil or other items. In general terms, all greases and oils are classified as fats. Fats are described in Webster’s Dictionary as energy-rich esters that occur naturally in animal fats and in plants and are soluble in organic solvents (as ether) but not in water. Chemically, fats are classified as triglycerides.

Oils are generally considered to be liquids, while greases are solid. Many animal fats and hydrogenated vegetable oils (Crisco®-type products) tend to be solid at room temperature. Fresh vegetable oils are generally liquid at room temperature and are sometimes referred to as virgin oils. Many consider the consumption of non-hydrogenated vegetable oils more favorably than hydrogenated products. Hydrogenated vegetable oils are more stable at cooking temperatures and last longer in frying equipment. For these reasons, both hydrogenated and non-hydrogenated vegetable oils are used in commercial food cooking (frying) operations. Recycled grease products are sometimes referred to as waste grease, byproduct grease, recycled grease or animal fats. These greases are generally low in cost, well adapted to certain industrial markets and widely used in livestock feed or pet food markets. Greases are generally placed into one of three categories:

1) Animal fats: are primarily derived as byproducts from animal meat processing facilities. The primary animal fats include edible and inedible tallow from processing cattle, lard and choice white grease from swine processing, and poultry fat from the processing of chicken, turkey or other birds. Since the supply source is fairly concentrated and the markets are well established, animal fat may be collected and sold by rendering companies or by the animal processors themselves. Another source of animal fats is the collection and processing of animal mortalities by rendering companies around the country. Collecting these waste byproducts not only provides valuable products for industrial uses, but also reduces the amount of material that might otherwise end up in landfills, posing pollution problems or a threat to the public health through the spread of disease. Livestock producers not serviced by a renderer may have to compost or bury animal mortalities. The increased demand for animal fats used in the production of biodiesel may help to increase the number of animal mortalities processed by renderers. The infrastructure for animal fats collection and distribution is well established. Less expensive animal fat products including inedible tallow, choice white grease and poultry fat are promising candidates for biodiesel production.

2) Yellow grease: is manufactured from spent cooking oil and other fats and oils collected from commercial or industrial cooking operations. Other fats may include grease rendered from hamburger, bacon or cooked meat entrees. For purposes of this discussion we will call this unprocessed mix of oils and grease products restaurant grease. Spent cooking oil may be vegetable oil or animal fat that has been heated and used for cooking a wide variety of meat, fish or vegetable products. After a period of time, the cooking oil is replaced with fresh product. At that time, the spent cooking oil may be collected by a rendering company or discarded. Less is known about the amount of yellow grease collected from low-level grease users or in rural areas where restaurants may be smaller or more remote. If the price of yellow grease were to increase, more small businesses might take advantage of the additional income available through renderers. Yellow grease is a relatively low value byproduct, often half the price of soybean oil. This low cost, well-developed collection system makes yellow grease a prime candidate for biodiesel production. Most of the biodiesel not made from soybean oil in the U.S. is produced from yellow grease.

3) Trap grease, sometimes referred to as brown grease: is collected from grease traps that are installed in commercial, industrial or municipal sewage facilities to separate grease and oil from waste water. Grease traps are sealed containers installed in sewer lines in a manner that allows the lighter grease and oil that is flushed down a drain to float to the top of the trap. These traps allow the water to flow under the grease and through to the main sewer or water treatment area. Grease traps are installed so that the top of the container can be opened, allowing the grease and oil to be removed. If traps are not periodically emptied, they become full, allowing grease and oil to flow directly into sewer systems. Given the potential for contamination from soaps and other chemicals, trap grease is not likely to command a premium for use in animal feed products. The water content of trap grease is also very high, resulting in a low yield-per pound collected. In many locations, water treatment facilities are large enough to process trap grease. In some areas like California, however, policymakers have considered requiring that trap grease be processed in rendering plants.

Uncertainty exists regarding the amount of treatment that would be required to make trap grease suitable for conversion into biodiesel. If it could be collected and processed, however, trap grease’s relatively low market value could make it a strong candidate for biodiesel production. Moreover, the prospect of a new market could raise the price of trap grease, thereby providing an incentive for increased collection and use. It is estimated that in the U.S., 13 pounds of trap grease is produced per capita, but less than one-third of that amount is actually collected. All of these waste or recycled grease products have potential for use in the growing biodiesel market. This general information section was adapted from a report entitled The Feasibility of Biodiesel from Waste/Recycled Greases and Animal Fats prepared for the Legislative Commission on Minnesota Resources.