Flat Iron Steak
Flat iron steak is a beef cut from the infraspinatus muscle in the chuck primal, specifically, the half of that muscle on either side of a connective-tissue seam that has been removed by modern butchery. Research from the Beef Innovations Group identified the serratus ventralis (Denver) and the deseamed infraspinatus (flat iron) as the second-most tender beef cut after tenderloin, despite being from the shoulder.
Flat iron steak is a beef cut from the infraspinatus muscle in the chuck primal, specifically, the half of that muscle on either side of a connective-tissue seam that has been removed by modern butchery. Research from the Beef Innovations Group identified the serratus ventralis (Denver) and the deseamed infraspinatus (flat iron) as the second-most tender beef cut after tenderloin, despite being from the shoulder.
The infraspinatus is a flat, fan-shaped muscle that sits on the outside of the shoulder blade. Until the early 2000s, it was generally ground or stewed because of a thick, tough connective-tissue seam running through its middle, anyone who tried to cook it as a steak got an inedible band of gristle through every bite. The "flat iron" innovation was figuring out how to butcher the muscle cleanly along that seam, leaving two long, flat, seam-free cuts that grill beautifully.
A flat iron steak is typically 1.5 cm thick, weighing 200-300 g per portion, oblong in shape (resembling a clothes iron, hence the name). It marbles well for a chuck cut, moderate to strong, comparable to a strip steak, and has a clean, fine grain running predictably along its long axis. Like all chuck-region cuts, the price is well below loin cuts despite the eating quality being competitive. The Australian name "oyster blade" reflects the muscle's shape; the French name "paleron" is the traditional braising name (used pre-deseaming).
Also known as: Top blade steak, Butler steak, Oyster blade (Australia), Paleron (France).
What good quality looks like
- An oblong, flat shape, 1.5 cm thick, 200-300 g per portion
- A clean cut surface with no visible connective-tissue seam, improperly-deseamed flat irons have a tough white seam through the middle and should be avoided
- Strong marbling for a chuck cut, comparable to strip-steak marbling on the same carcass
- Fine grain running along the long axis of the cut
- Bright red lean color, white firm fat
How to cook it
- High direct heat: cast iron or grill, 3-4 minutes per side. Pull at medium-rare (54-58°C / 130-136°F)
- Rest 5 minutes, slice across the grain at a 45-degree diagonal, flat iron grain runs lengthwise, so slicing direction is essential
- No marinade needed, flat iron's marbling carries the flavor naturally
- Best applications: weeknight steak dinner, steak salad, fajitas, steak sandwiches
Frequently asked
What is the flat iron steak?
Flat iron is one of two halves of the infraspinatus muscle (chuck primal, top of shoulder blade) after a thick connective-tissue seam through its middle has been butchered out. Identified in 2002 by Beef Innovations Group research as the second-most tender beef cut after tenderloin. Now widely available at US butcher counters and supermarkets.
Why was flat iron unknown before the 2000s?
The infraspinatus has a thick connective-tissue seam running through its middle. Cooked as a whole muscle, the seam stays tough and chewy, ruining the eating experience. Until research identified the muscle's tenderness potential and developed a butchery technique to remove the seam cleanly, the muscle was generally ground or stewed. Modern flat iron is the deseamed half-muscle, ready to grill.
How does flat iron compare to Denver?
Both are chuck-region cuts that grill like loin cuts. Flat iron is from the top of the shoulder blade (infraspinatus); Denver is from underneath the shoulder blade (serratus ventralis). Tenderness is comparable. Marbling is comparable on the same carcass. Pricing is similar. Flat iron has a more pronounced grain; Denver has a finer grain. Both are excellent value picks.
How thick should a flat iron be?
1.5 cm (0.5-0.75 inch) is the most common thickness, perfect for fast high-heat cooking. Thicker portions (2.5 cm) are sometimes available and benefit from a brief reverse-sear. Thin-sliced flat iron (under 1 cm) can be used for stir-fry or sandwich beef.
How does MeatGrader score flat iron?
MeatGrader scores flat iron on marbling, color, grain quality, and the absence of residual connective-tissue seams. Score expectations are calibrated against typical chuck-region marbling rather than loin-region marbling, a Choice-tier flat iron from a Prime carcass is the realistic upper bound.