What the Cut?: Flank & Skirt Steak

Flank and skirt steaks are often mistaken for one other when shopping for meat. Equally delicious and sometimes interchangeable, there are some unique characteristics to consider when choosing which is best for your dish.

Flank Steak

The flank steak is the more straightforward of the two cuts. It comes from the flank primal, which is the first primal removed from the hindquarter of a beef carcass (a primal are the section of meat that are broken down into individual cuts). The flank primal is below the loin and in front of the round. It’s the only primal that is considered boneless, with the exception of sometimes including a portion of the 13th rib.

The flank primal is a portion of the abdominal wall and supports a lot of the animal's weight. The musculature is thin but very strong and provides a strong beef flavor with a firm texture. The muscle strands are long and thick, giving the cut a distinct striated look.

Flank steaks are long, flat and relatively fat-free. They have a thick membrane on one side and need little preparation once the membrane is removed — most butchers have or will do this for you. All that's usually left to do is remove a small, oval shaped piece of silver skin from the thicker end of the steak. A knife slides easily under the silver skin and can be discarded.  Trim and square-up any tapered or hanging edges. Score the steak with a shallow cross-hatch to prevent curling when cooked.

Flank steaks can be grilled or seared whole, or sliced thin and cooked in stir-fry or fajitas. They usually benefit from tenderization and marinades, especially citrus based. To insure that your flank steak is succulent and juicy with a firm but not chewy bite, be sure to cook rare to medium and cut perpendicularly to the grain of the meat.

A 3 ounce serving of cooked flank steak contains:

• 160 calories
• 23g protein
• 2.6g saturated fat
• 1.5mg Iron
• 4.3mg Zinc

 Skirt Steak

Skirt steaks come from the plate primal and are located on the forequarter of the side. Below the rib and behind the brisket, the plate primal is directly in front of the flank primal on a whole side of beef. There are two distinct cuts on a side of beef that are considered skirt steaks, the inside skirt and the outside skirt. Both steaks have a long, ribbon-like shape with large muscle fibers but their misleading names are what makes it difficult to remember which-is-which.

Inside skirt steaks are larger and generally cut from the flank primal but also extends onto the plate primal. They make up a portion of the animal’s core muscles of the abdominal wall. Outside skirt steaks are the animal's diaphragm and are attached to the plate primal only. They have a deep red color due to the constant work needed to control breathing. The more a muscle works, the more oxygen is needed to support it's function. Since blood is the delivery mechanism for oxygen to muscle cells, more myoglobin — a protein found in blood — is left behind in the muscle cells, leaving a deeper red hue. If you recall our flash freezing series, this is the same protein that gives Drip Loss it's blood-like appearance. 

Now for the confusing part. If you are looking at a whole animal, inside skirt steaks are located closer to the outside of the body and outside skirt steaks are located deeper inside the body cavity. Seems a little backwards doesn't it? 

Think about it from the perspective of the butchers who named these cuts. When an animal is processed, it is split in half down the length of the body making two sides. The sides are cut in half again, but this time down the sides of the animal leaving the fore (front) and hind (rear) quarters. When the butcher begins to break down the quarters into primals, the body cavity, or what was the inside of the animal, is facing out and away from the cutting table. 

Where the outside skirt steak was formally located on the inner portion of the animal, it is now on the outside. Hence, outside skirt. Likewise, the inside skirt is located inside the quarter and away from the surface giving us the inside skirt. Make sense? If not, that's okay. Just remember that the names are opposite of their anatomical locations. The name-location relationship of these two skirt steaks is important to understand because due to their location, they have distinctly different flavor profiles.

Outside skirt steaks are ubiquitously labeled as “skirt steak,” getting the honor because it is the more unique of the two skirts. Located inside the body cavity, it has a deeper, beefier flavor than inside skirts, due to their proximity to the organs. Inside skirts have a few layers of fat and other tissues separating them from the organs, so their flavor is less robust compared to the outside skirt. In fact, once cooked and sliced, one would be hard pressed to tell the difference between an inside skirt steak and a flank steak. They are more difficult to access and are usually reserved for flap or ground meat.

Note: From this point forward, because most retail skirt steaks are outside skirt steak, when you see “skirt steak”, it is referring to the outside skirt steak.

Skirt steaks are usually less than a 1/2’ thick and can be as long as 24 inches. They have thick membranes covering both sides that can be easily peeled away once the edges of the steaks are trimmed off. This is usually done before retail sale but if not, trim away about a 1/4 inch off the edge of the steak and slide a knife under one side until there is enough to hold onto, then start to pull away, placing a free hand on the steak to hold in down. Underneath will be a significant amount of intra- and intermuscular fat deposits that should be left for flavor and self-basting while cooking.

Like flanks, skirt steaks take well to marinades and must be cut perpendicularly to the grain, leaving a supple and juicy bite. The ribbons can be cut down to fit any size pan or the entire piece can be laid across a grill. Skirts are best when rare to med-rare so no matter what marinade is used (ahem, chimichurri), the best results come from inferno-hot and fast cooking. Whether you are using cast iron or a grill, you’ll need to get it as hot as possible so that a nice crust can form on the surface with only cooking a minute or two on each side. Cook outside or open all the windows and put a shower cap over the smoke detector.

A 3 ounce serving of unmarinated, cooked skirt steak contains:

• 240 calories
• 23g protein
• 6g saturated fat
• 4.4mg iron
• 6mg zinc 

Flank or Skirt?

Both flank and skirt steaks do really well cooked whole or sliced, so think about the process for the dish to make the best choice. Since most household stoves don’t have the BTUs to get a wok or large pan hot enough to cook stir-fry like the pros, your best bet is a 1/4”-1/2” sliced flank steak because it is more suited for longer cooking. Same goes for fajitas. If you are lucky enough to have a big burner that goes to 11 and a proper wok or comal, then go with skirt steak as it has a deeper, juicer flavor.

If you are grilling or searing whole and serving as the protein on a composed dish (protein+veg+starch/grain), I choose skirt steak every time. It takes no time at all to make a juicy and flavorful meat that has a range of textures. Just be sure to get the grill or pan freakishly hot. On that note, if using cast iron, you will probably still need some sort of high-temp oil to help prevent sticking, It's better to brush the meat with the oil instead of adding a layer to the pan to prevent the oil from burning or igniting immediately.

On a high-fat diet? Go with skirt. Trying to eat leaner? Choose flank.

Finally, skirt steaks are almost the perfect camping steak. You can marinade ahead of time and roll them up to take up less room in the cooler. Plus, when cooking over a campfire, temperature doesn't matter as much... as long as it's screaming hot. They cook quickly and you don’t have to worry about setting off the fire alarm. I have even cooked a skirt steak directly on white hot coals, no pan or nothin’. It was magical.