Beef tenderloin is a sub-primal cut of beef that spans two primal cuts, the short loin and the sirloin. In some parts of the world it is known as the eye fillet, fillet, or tenderloin. It consists of the psoas major muscle and is located under the ribs next to the spine. It is known as the most tender of all cuts of beef and is not a very large muscle in relation to the total size of a cow. For these reasons, as well as its fine flavor, it is generally the most expensive cut of beef as well.
Several famous dishes, including filet mignon steak and Chateaubriand, make use of beef tenderloin. Other dishes requiring very tender beef sometimes use this cut as well. It has a very fine texture and is extremely tender. It is also fairly lean, but has a very rich flavor despite a relatively low fat content, although some higher grades can exhibit more marbling.
The distinctive shape of a beef tenderloin makes it easy to recognize. It is usually no more than 18 to 24 inches (45 to 60 cm) long, and is roughly cylindrical in shape with one end, called the tail, tapering to a point, and the other end, called the butt, having a larger thicker profile created by two attached lobes. The center section is used for filet mignon and Chateaubriand. The tail is not usually used for steaks because of its shape. The butt end is suitable for steaks, but they will be thinner than a typical filet mignon and are usually just called tenderloin steaks.
Since it spans two primal cuts, part of the beef tenderloin is sometimes included as part of one of these two sections, the short loin. In this case, it is paired with the strip loin and cut as porterhouse steaks. Porterhouse steaks have a T-shaped bone separating a portion of tenderloin and a portion of strip loin.
Most cuts of beef tend to be suitable for cooking in one particular fashion. Beef tenderloin is one that benefits from a number of cooking techniques. Steaks can be seared or grilled and tenderloin roasts are very fine dishes. Very thinly sliced high-quality beef tenderloin can even be served raw as the dish known as beef carpaccio.
Like other cuts of beef, tenderloin is graded according to quality, but even the lowest grades are highly desirable. Meats are generally graded according to several factors but primarily according to the fine veins of fat that permeate the meat, known as marbling. Steaks that exhibit a high degree of marbling are generally given a higher grade. Certain extremely fine beef tenderloin steaks from specially raised and tended beef cows from the Kobe region of Japan are called wagyu beef can fetch hundreds of US dollars or more per pound (0.45 kg).