The fat content of yellow grease is generally 100 percent. Yellow grease is derived from the collection and processing of primarily restaurant grease, but it can contain dark-colored tallow. Because restaurants have been using primarily vegetable oils for frying, yellow grease is primarily vegetable oil. These cooking oils are exposed to higher temperatures and moisture so they have a higher maximum level of free fatty acids (10 to 25%) that can turn rancid. When purchasing supplies of yellow grease, select those that have lower levels of free fatty acids and contain antioxidants. Thus, yellow grease is variable in quality, and you should remain with a reputable supplier.
Mike Hutjens, Extension Dairy Specialist, University of Illinois - Illini DairyNET
