The beef industry has invested a significant amount of time and money over recent years in finding new ways to break down a steer. Many previously unregarded portions of the carcase have been pushed into the limelight as a result. Some, like the flatiron steak or Santa Fe steak, were developed by isolating tender muscles in otherwise tough regions. Others, like flank, hanger, flap or skirt steak, were popular in other cuisines but previously unknown to most Americans. Many of these are fairly similar cuts, and it is difficult for a layperson to recognise the difference between flap and skirt.
The Flap Steak
The flap steak, or flap meat as it is also called, is a small cut found in the short loin. Technically known as the obliquus internus abdominis muscle, it is a flat layer of muscle found on top of the tri-tip. It is cut from the tri-tip by slicing horizontally through the layer of fat and connective tissue that binds them together. Once trimmed, the flap is a thin piece of relatively tender beef, with long muscle fibres similar to those of the beef flank.
The Skirt Steak
There are two types of skirt steak, the inside and the outside portions, both cut from the "plate" portion of the steer's abdomen. The outside portion is slightly larger. There are a total of four skirt steaks on a carcase, but they are relatively small and in an average steer they will only total 3.63kg. of trimmed beef. Like the flank and flap steaks, skirt steaks have long, chewy fibres, but can be tender if prepared correctly.
The Differences Between Skirt and Flap
Although skirt and flap are similar in some respects, they are easily distinguished in their uncooked form. Skirt steaks are long but narrow strips of meat, resembling a rack of ribs but without the bone. They have also been likened to a belt, or "faja" in Spanish, which is the root of the word fajita and the origin of the food term. The flap is much smaller, and is an irregular square or polygon in shape.
The skirt steak is primarily known as the original and authentic cut of beef for fajitas. Some is used for other purposes, primarily as bistro steaks, but the popularity of fajitas and the limited supply of skirt steak makes this rare. Beef flap can also be used as fajita meat, but is more commonly prepared as a bistro steak. This is a class of thin, fibrous cuts that yield a chewy and flavourful steak when grilled or broiled, then sliced across the grain. Flatiron steak and hanger steak, or onglet, are also popular for this purpose.