Filet mignon comes from the psoas major, a deep postural muscle that runs along the spine of the cow. This muscle does almost no heavy work during the animal’s life, which is exactly why it produces the most tender cut of beef available.
Where the Psoas Major Sits
The psoas major is a long, ribbon-shaped muscle that starts just below the ribs, runs alongside the spine through the lower back, and extends down into the hip area. In a living animal, its main jobs are stabilizing posture and helping flex the hips and upper legs. It’s buried deep inside the body cavity, shielded by the spine and surrounding muscles, so it bears almost none of the mechanical stress that leg and shoulder muscles handle daily.
In beef processing terms, the psoas major is the core of what butchers call the tenderloin, a long, narrow subprimal cut taken from the loin and sirloin sections along the back half of the animal. The entire tenderloin can be roasted whole or sliced into individual steaks. Filet mignon specifically refers to steaks cut from the narrower tip end of the tenderloin, typically one to two and a half inches thick. The French name translates loosely to “small cut.”
Why This Muscle Is So Tender
Tenderness in beef comes down to connective tissue, specifically a protein called collagen that forms a structural web around and within muscle fibers. Muscles that do heavy locomotion work, like those in the legs and shoulders, build up much more collagen to handle the repeated stress. The psoas major, by contrast, is a postural muscle. It holds the lower back stable and assists with subtle hip movements, but it never powers the animal forward or supports its full weight. The result is one of the lowest collagen concentrations of any muscle in the carcass.
That low collagen content means filet mignon stays tender regardless of how you cook it. Most tough cuts need slow, moist cooking methods to break down their connective tissue. Filet mignon doesn’t have that problem, which is why it’s almost always prepared with quick, high-heat methods like pan searing or grilling. The longissimus thoracis (the muscle behind ribeye and strip steaks) shares a similarly low collagen profile for the same reason: it’s a support muscle, not a workhorse.
Tenderloin vs. Filet Mignon
People often use “tenderloin” and “filet mignon” interchangeably, but they’re not quite the same thing. The whole beef tenderloin is a tapered cut roughly 18 to 24 inches long. The thicker center section is sometimes sold as chateaubriand or cut into tournedos. Filet mignon comes from the tapered, narrower end, yielding smaller, more uniformly round steaks. Because this tip portion is the most delicate part of an already tender muscle, it commands the highest price per pound of virtually any beef cut.
Cooking to Match the Cut
Filet mignon’s tenderness is its defining trait, but it carries less intramuscular fat (marbling) than a ribeye or strip steak. That means it delivers a buttery, mild flavor rather than the rich beefiness of fattier cuts. Many cooks compensate by wrapping it in bacon, finishing it with compound butter, or pairing it with a rich sauce.
The USDA recommends cooking beef steaks to an internal temperature of 145°F, followed by a three-minute rest. Many restaurants and home cooks serve filet mignon at lower temperatures for a rarer center, typically around 125°F for rare or 130 to 135°F for medium rare. Because the cut is thick relative to its diameter, it benefits from a reverse sear: starting in a low oven to bring the interior up to temperature evenly, then finishing in a screaming-hot pan for a crust. This approach avoids the gray band of overcooked meat that can form when you sear a thick steak first.