Skirt steak is one of the most flavorful cuts of beef, and even though it's also one of the tougher cuts with a lot of connective tissue, it's still a great steak for grilling. Skirt steak comes from either of two separate muscles inside the chest and abdominal cavity, below the ribs, in the section of the cow known as the beef plate primal cut. The two muscles are the diaphragm muscle, called the outside skirt, and the transversus abdominis muscle, or inside skirt.
What Is Skirt Steak?
Inside and outside skirt are pretty similar; both are long, flat muscles with very thick grain that runs across the length of the muscle. These narrow pieces of meat can be about 20 to 24 inches long and three to four inches across once they've been trimmed.
Because there are only two skirt steaks per side of beef, one inside and one outside, pretty much every outside skirt from every side of beef ends up in a commercial kitchen of some kind. So when you see skirt steak at the butcher shop, it will almost always be an inside skirt.
Outside skirt is encased in a membrane which needs to be removed before preparing it. If the meat has been dry-aged, that membrane will be like paper and will peel off pretty easily. With wet-aged meat, the membrane will be wet, and it's a little bit trickier to peel it off without tearing the meat. A good butcher will have peeled and trimmed the steak before sale.
How to Cook Skirt Steak
Both outside and inside skirt have a good amount of fat within and between the muscle strands, which helps keep it moist when grilling it. The grain on the inside skirt is a little bit wider, so it might have slightly more fat.
A lot of skirt steak recipes call for marinating the meat before grilling it, and because of its looser structure, skirt steak will absorb the flavors of the marinade quite well. But there's no need to marinate it for more than 30 minutes or so, as marinating does not tenderize meat.
Since skirt steak is tough, the best way to cook it is very quickly over the hottest grill you can get. As a matter of fact, some people will even skip the grill altogether and cook it directly on the coals. This actually works quite well, because you do not want to overcook skirt steak. Cooking it directly on the coals gets the surface of the meat nice and brown very quickly, without cooking the inside of the meat for too long. Ideal doneness is medium-rare to medium.
Most importantly, skirt steak absolutely must be sliced thinly against the grain. Because it's so long, your best bet is to cut it into shorter sections first and then slice those sections across the grain.
What Does Skirt Steak Taste Like?
Skirt steak has an intensely beefy flavor—even more flavor than the flank steak, which is similar in shape and size. Skirt is an ideal steak for marinating and will easily take on those flavors.
Varieties of Skirt Steak
The skirt steak you purchase or eat will either be outside skirt or inside skirt. Outside skirt is attached to the outside of the chest wall (hence the name), running diagonally from the 6th to the 12th rib. It's covered with a thick membrane which is the diaphragm itself (the steak is the muscle that moves the diaphragm).
Inside skirt is situated below and a little bit further back from the outside skirt. It is located within the body wall itself, which is why it's called "inside." The inside skirt muscle lies flat across the lower part of the ribs and extends even beyond the ribs, into the beef flank primal cut, which is part of the hindquarter of the animal. As a result, a wide flap of meat at the rear of the transversus abdominis muscle is usually excluded and ends up part of the flank instead.
Outside skirt is a bit thicker than the inside skirt and it's more uniform in shape. Inside skirt is thinner, with a slightly more irregular shape. A whole inside skirt might weigh two pounds; an outside skirt may be a bit less. But inside skirt will shrink a bit more when you cook it as the muscle fibers tighten up.
Because of its thickness and regular shape, the outside skirt is what restaurants and other foodservice operations prefer to use for making fajitas and other grilled skirt steak dishes.
Recipes for Skirt Steak
Although perfect on a hot grill, you can also cook a skirt steak in a cast-iron skillet or under the broiler—or anything else you can get extremely hot. Just remember, you need to cook this cut very hot and very fast. Under no circumstances should skirt steak be cooked past medium-rare; it will be way too tough.
If you're making fajitas or any other stir-fry dish, slice it up first (against the grain), then marinate and cook it.
Where to Buy Skirt Steak
You should be able to find skirt steak in the meat department of your supermarket, more often the inside skirt versus the outside skirt (but may be labeled simply as "skirt steak.") Most of the surface fat (as opposed to the intramuscular fat) should have been removed by the butcher.
Although skirt steak and flank steak are two different cuts of meat, the two are referred to interchangeably. But they should both be labeled separately as such.
How to Store Skirt Steak
Your package of skirt steak from the grocery store or butcher can be stored in the refrigerator for three to five days and six to 12 months in the freezer when wrapped airtight. If you have cooked the meat already, it will stay fresh in the fridge for around four days and can be kept in the freezer between two and three months.