With beef and other meats, the various retail cuts belong in two categories. One group consists of little-used muscles, which produce correspondingly tender meat particularly suited to grilling. The other group contains the heavily used muscles, which yield flavorful but tough meat filled with connective tissue. For many cooks, the sirloin makes an excellent compromise between tenderness and flavor.
About the Sirloin
The sirloin occupies the area near the rear of the steer between the tender cuts of the loin and the chewier cuts of the round and flank. The upper portion of the sirloin, closest to the loin physically, seems more like the loin in its tender texture. The lower portion of the sirloin contains several muscles with varying degrees of tenderness; on the whole, it's less tender than the upper portion.
The upper, or top sirloin, generally appears in supermarkets as steaks or roasts, and can be purchased either on the bone or boneless. The bone-in steaks are referred to as pin-bone, flat-bone, round-bone or wedge-bone steaks, depending on which portion of the bone remains. The pin-bone steak, the most tender one, comes from the area directly behind the porterhouse. Deboned, the same steaks get sold as boneless top sirloin. Top sirloin roast, sometimes called baron of beef, comes in second only to prime rib for tenderness and flavor.
The lower, or bottom sirloin can also be purchased as a roast, but more commonly gets broken into smaller sections. For example, the relatively tender tri-tip, a triangular muscle located within the bottom sirloin, can be cut out and sold for roasts, bistro steaks, kebabs and similar uses. Other bottom sirloin cuts include the ball-tip roast and flap steak, which are chewier than top sirloin but enjoyable when they're thinly sliced.
Choosing Top or Bottom Sirloin
It's difficult to say that top or bottom sirloin is inherently better. The cut you favor should reflect your planned use of it. Tender top sirloin is better suited to use as a steak for grilling or broiling, or as a roast for quick cooking to rare. Though not suited for use as a grill steak, most bottom sirloin cuts make excellent roasts, stew meats or bistro steaks, which are grilled or broiled whole and then thinly sliced into strips. Bottom sirloin generally costs less than top sirloin, and therefore presents better value when used.