If your going to grind in beef fat make sure you use fat and not suet. Suet has very high melting point do to the increased amount of triglyceride, which will make for an unpleasant experience in say a medium rare burger. The absolute best fat to use in grinds is off the outside of the loin or the outside of the hinds, be it beef or pork. Suit ( kidney fat ) is best used in some limited baking applications.