Cut vs cut
Flank Steak vs Skirt Steak
The short answer
Different muscles doing different jobs. Skirt is the diaphragm — it works with every breath the animal takes, which is why it tastes so strongly of beef — and it is thin, loose-grained and fatty. Flank is the abdominal wall: leaner, thicker, flatter, with one long uniform grain. Both are ruined the same two ways.
Flank Steak
The abdominal wall — rectus abdominis. Flat, lean and fibrous, with a pronounced grain running the length of the steak, which makes it the easier of the two to carve neatly: one direction, straight across. Lean enough that a marinade is doing real work rather than decorating, and lean enough that past medium-rare it eats like rope.
Skirt Steak
The diaphragm, sold as inside and outside skirt. A muscle that contracts constantly for the animal's whole life, which is where the flavor comes from — nothing else this cheap tastes this strongly of beef. Loose-grained enough to take a marinade in under an hour, thin enough to be done before the interior knows it is on the fire.
Side by side
| Flank Steak | Skirt Steak | |
|---|---|---|
| Primal | Beef flank | Beef plate |
| Muscle | Rectus abdominis — abdominal wall | Diaphragm (inside and outside skirt) |
| Fat | Lean | Moderate — noticeably fattier |
| Flavor | Beefy and straightforward | Much stronger — the most intense of the cheap steaks |
| Thickness | Thicker, even across the steak | Thin and uneven |
| Grain | Runs the length — slice straight across the width | Runs the short way — cut into 4–6 inch sections first, then slice each |
| Cook time | A few minutes a side | Two minutes a side over high heat |
| Best for | Slicing onto a platter, stir-fry, salads | Fajitas, tacos, arrachera |
| Also sold as | London broil, jiffy steak | Arrachera, fajita meat, inside or outside skirt |
The verdict
Which one to buy
Skirt for anything going into a tortilla, or anything cooked over a fire hot enough to be uncomfortable to stand next to — it has more fat, more flavor, and it is done in two minutes a side. Flank for neat slices on a platter, a stir-fry, or a cold salad the next day, and when you need one piece to feed more people. If you are buying blind and don't yet know what you'll do with it, buy flank: it is more forgiving to carve and it stretches further.
Two thin steaks from the underside of the animal, both fibrous, both cheap once and expensive now, and
both ruined by the same two mistakes: cooking them past medium-rare, and carving them the wrong way.
Why skirt tastes like that
The diaphragm never stops working. Muscles that work hard build myoglobin and connective tissue and,
with them, flavor — which is why skirt, hanger and other working muscles taste more intensely of beef than
the loin cuts that cost four times as much. Skirt is thin and loose-grained enough to get away with it.
Flank sits further back and lower down, in the abdominal wall. It works, but not like that. Leaner,
flatter, thicker, and cleaner tasting.
Cooking
Get the fire as hot as it goes. Skirt needs about two minutes a side; flank a little more. Pull both at
medium-rare. Neither has enough fat to survive being held past that.
Carving
Rest, then find the grain before the knife goes anywhere. Flank's runs the length of the steak, so cut
straight across the width. Skirt's runs the short way, so cut the long band into 4–6 inch sections first,
then slice each section across its fibers. Thin either way — the thinner the slice, the shorter the fiber,
and fiber length is what your teeth are actually fighting.
Common questions
Which one is the real fajita steak?
Skirt. The word comes from *faja*, a belt or sash, which is the shape of the cut. Flank became the common substitute once skirt stopped being cheap, and it works. It just isn't the original.
What is the difference between inside and outside skirt?
Two different parts of the diaphragm. Outside skirt is thicker and more even, and is generally the better piece; inside skirt is wider, thinner and far more common at retail. They cook the same way, but the thin inside skirt overcooks faster — give it less time, not the same.
Do I have to marinate them?
No — salt and a hot fire is enough for either. Marinade helps more here than it would on a ribeye because the loose grain absorbs it quickly, and because salt and acid do measurable work on a fibrous muscle. What no marinade can fix is cooking either one past medium-rare.
Why does everyone insist on slicing across the grain?
Because on these two the grain is coarse, long and strong enough to be the difference between tender and inedible. It also runs differently on each: flank's fibers run the length of the steak, so you slice straight across the width. Skirt's run the short way across a long band, which is why you cut it into 4–6 inch sections first and then slice each one. Thin, in both cases.
Buy Flank Steak or Skirt Steak
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Flank Steak
The abdominal wall — rectus abdominis. Flat, lean and fibrous, with a pronounced grain ...
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Skirt Steak
The diaphragm, sold as inside and outside skirt. A muscle that contracts constantly for...
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