Natural form

Raw flank steak showing its wide, flat shape and pronounced coarse grain running lengthwise.

Establishes the cut's distinctive flat, broad shape, coarse muscle grain, and deep red lean beef color so readers can recognize it at a butcher counter.

Proteins

Flank Steak (Vacío)

Lean, broad beef cut with bold flavor, grilled and sliced thin against the grain.

Flank steak is a lean, flat cut from the beef belly with a coarse, pronounced grain and robust beefy flavor. It is marinated and grilled or seared hot, then sliced thinly across the grain for tenderness, common in fajitas, stir-fries, and Argentine vacío. Overcooking toughens it, so it shines cooked to medium-rare.

Flank steak — known as vacío throughout the Southern Cone — comes from the belly of the cow, specifically the flat abdominal muscles below the loin. It is a single, broad, rectangular cut with a thin fat cap that is usually removed, leaving a very lean piece of meat with long, coarse muscle fibers running lengthwise along the entire steak. What defines vacío is not its marbling but its bold, beefy flavor and its ability to absorb marinades deeply, making it a prized cut across Argentine asado, Mexican fajitas, and Chinese stir-fry alike. In the United States it appears on labels as flank steak; in markets with South American populations it may be labeled vacío. The cut is lean enough to dry out quickly, and its fibers are unforgiving if sliced incorrectly — this is not a cut you can cook and rely on tenderness from fat. The trade-off is reward for care: a properly cooked vacío sliced against the grain yields tender, yielding bites from an otherwise tough muscle. It is not a premium steakhouse cut — it is a cook's cut, one that rewards technique over quality grade, though USDA Choice or better will offer the best balance of flavor and moisture.

A 1.5–3 lb vacío is typically sold as a single whole steak, 1–1.5 inches thick at the center. Its yield is roughly 80% after cooking and slicing, dropping sharply if overcooked, because the lean meat loses moisture rapidly past medium-rare. The best vacío — the tapa de vacío — comes from the outer edge of the flank and carries slightly more intramuscular fat, making it more forgiving. The bone-in variant (vacío con hueso) retains the small rib section and is the traditional form for Argentine asado, where the bone adds flavor and helps anchor the cut on a wood-fired grill.

In Argentine and Uruguayan cooking, vacío is the cornerstone of asado culture. Seasoned with nothing more than coarse salt (sal gruesa) and grilled over hardwood embers, it is the cut that defines a simple, communal asado. The flavors — the char, the beef, the herbaceous punch of chimichurri — are inseparable from the identity of the dish. Understanding vacío means understanding that it is built for bold, bright accompaniments: acidic sauces, fresh herbs, fermented condiments. Used as fajita meat or in a steak salad, the vacío adapts to different cuisines while retaining its essential character: lean, broad, and intensely flavored when treated with respect.

Measured in: g
Storage: Fridge

Types & varieties

Vacío con hueso

With small rib bone attached; more flavor and traditional for Argentine asado; the bone helps anchor the cut on a wood-fired grill.

Vacío sin hueso

Boneless; easier to slice and serve; identical in flavor and texture to the bone-in version.

Tapa de vacío

Thin, more marbled variant from the outer edge of the flank; more forgiving on the grill and slightly more tender.

Skirt steak

Different cut (from the diaphragm, not the flank); functionally similar for many preparations; often confused with flank in English-language markets; cook identically.

The Grain: The Single Most Important Thing About Vacío

Before you cook this steak, understand that its long, coarse fibers run from one end of the cut to the other, parallel to the long edge. These fibers are what make flank steak tough when sliced with them, and tender when sliced across them. The mistake most home cooks make is slicing with the grain because the whole steak is easier to cut that way. The fix is simple: after the steak rests, pick it up and look at the surface. You will see lines running in one direction. Turn the steak 90 degrees and cut perpendicular to those lines. For a 1.5-lb vacío, this produces thin strips, about 1/4 inch or less. The difference between correct and incorrect slicing is the difference between a steak that melts in your mouth and one that requires heavy chewing. There is no workaround — the grain is non-negotiable.

Run your fingers across the cooked steak surface to feel the grain direction before slicing
Cut 1/4-inch slices or thinner at a 90° angle to the grain
Do not slice the whole steak in one direction without checking the grain first — the fibers are easy to see and feel

Marinade Strategy for Lean Meat

Because vacío has virtually no intramuscular fat, it benefits from a well-designed marinade more than a typical steak. The goals are two: add moisture and break down surface fibers to improve penetration of flavor. Acidic ingredients — lime juice, vinegar, buttermilk, or wine — chemically tenderize the outer surface. Oil seals in what moisture the meat already has. Aromatics (garlic, cumin, herbs) contribute flavor. A minimum of 2–4 hours in the refrigerator is necessary for the acid to do meaningful work; overnight is better. Do not exceed 24 hours, as the acid will eventually turn the surface mushy rather than tender. If you skip marinade, score the surface in a crosshatch pattern with a sharp knife to allow oil and salt to penetrate.

Use 2–4 tablespoons of acid (lime or red wine vinegar) per 1.5 lbs of vacío
Add oil at roughly 1 part acid to 2 parts oil — enough to coat the meat without drowning it
Include salt in the marinade — it helps the meat retain moisture and improves flavor penetration

Common uses

Grilled whole and sliced thin for fajitas, tacos, and burrito bowlsSliced thin for stir-fries and lo mein fillingsGrilled and sliced for steak salads with robust dressings (blue cheese, vinaigrette)Thinly sliced raw for carpaccio-style applications with olive oil and shaved ParmigianoAguapanela-style ceviche or raw tartare preparations with citrus and herbsTraditional Argentine asado, grilled over wood or charcoal fire with sal gruesaBroiled or pan-seared and finished with compound butterStuffed and rolled (paupiettes) with herbs, cheese, or bacon before grillingSliced for grain bowls with roasted vegetables, chimichurri, and pickled onions

Tips & pitfalls

Slice against the grain — this single step determines whether the steak is tender or chewy. Identify grain direction before cooking, and confirm it after the steak rests.
Marinate 2–4 hours minimum; the lean meat benefits from acidic tenderizers (lime juice, vinegar, buttermilk) and oil to retain moisture.
Bring to room temperature 30–45 minutes before cooking for even doneness throughout the steak.
Use high heat and cook quickly — 4–6 minutes per side for a 1.5-lb steak yields medium-rare; do not exceed this.
Rest 5–10 minutes after cooking before slicing; this allows juices to redistribute and prevents moisture loss.
Score the surface in a crosshatch pattern if skipping marinade to help salt and oil penetrate the lean meat.
Remove the silver skin (thin, chewy membrane) if present — it will not break down with cooking and will be unpleasant to eat.
For the most tender results, pound lightly with a meat mallet to slightly flatten and break fibers before marinating.
Common mistake: slicing with the grain because the steak is easier to cut whole — always rotate the steak 90° after cooking to find the grain, then slice perpendicular to it.
Overcooking past medium-rare is the other primary error; use a probe thermometer and remove from heat at 140°F (60°C) for carryover cooking to 145°F (63°C).
For Argentine-style asado, season only with coarse salt (sal gruesa) and grill over hardwood embers — the simplicity of the preparation honors the cut's bold beefy flavor.

Nutrition

No USDA FoodData Central match for Flank Steak (Vacío) yet. We surface a per-100 g profile once a generic whole-food entry is matched and verified.

In the shops

Matched grocery products

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Good to know

Cut location: Belly (flank) of the cow, from the abdominal muscles below the loin
Alternative names: Vacío (Argentina, Uruguay, Chile, Paraguay), sobretapa, sobrecostilla, picaña (Brazil)
Typical weight: 1.5–3 lbs (700g–1.4kg) per steak
Fat content: Very lean; thin fat cap optional, usually removed
Fiber structure: Long, coarse muscle fibers running lengthwise along the steak
Best doneness: Medium-rare (145°F / 63°C); overcooking causes toughness and dryness
Fridge storage: 1–2 days raw; 3–4 days cooked, tightly wrapped
Freezer storage: Up to 3 months, well-wrapped
Cooking yield: ~80% after cooking and slicing; shrinks noticeably if overcooked
Key preparation: Must be sliced AGAINST the grain after cooking to break fibers and achieve tenderness
USDA grade: Typically Choice or Select; Prime for best marbling and moisture retention

Substitutes

Skirt steak — Slightly more marbled; from the diaphragm rather than the flank; cook identically to vacío; the closest substitute in most markets.
Hanger steak — Butcher's cut with intense, beefy flavor; shares the same slicing and doneness rules as vacío; slightly more robust texture.
Flat iron steak — From the top blade of the shoulder; more tender but thinner; reduce cooking time accordingly to avoid overcooking.
Tri-tip — Different grain structure (fibers radiate from a central point in a triangular shape); requires careful slicing to cut across all grain directions; works well for grilling whole.

Pairs with

ChimichurriAji amarillo or fresh ají peppersLime, garlic, cuminWorcestershire sauce and soy sauceCaramelized onions and peppersProvoletaSalsa verde / mojo verdeBlue cheese or aged cheddarGrilled corn and potato

Also called

Vacío