2,339. Permitted Fats

Maachalos Assuros 7:7

Fat that’s covered by meat is permitted. The Torah prohibits the fat on the flanks but not the fat that’s within the flanks. Similarly, the fat on the kidneys is prohibited but not the fat within the kidneys. Regardless, one must remove the white in a kidney before eating it, though one need not pry out every last vestige of it.

Maachalos Assuros 7:8

There are two strands of fat in the main area of the loins, by the top of the thigh. When an animal is alive, this fat is found on the intestines, but when it dies, two pieces of meat stick together and cover this fat so it can’t be seen until the pieces of meat are separated. This fat is prohibited because it’s not fat that’s covered by meat. When you find fat under meat so that the meat completely surrounds it and it can’t be seen until the meat is cut off, then it’s permitted.