What's the best prime rib to buy, and is prime rib really "prime"?
Butchers tend to cut a rib roast, which consists of ribs 6 through 12 if left whole, into two distinct cuts. The more desirable of the two cuts consists of ribs 10 through 12. Since this portion of the roast is closer to the loin end, it is sometimes called the “loin end.” Other butchers call it the “small end” or the “first cut.” Whatever it is called, it is more desirable because it contains the large, single rib-eye muscle and is less fatty. A less desirable cut, which is still an excellent roast, consists of ribs 6 to 9, closer to the chuck end, and sometimes called the second cut. The closer to the chuck, the more multimuscled the roast becomes. Since muscles are surrounded by fat, this means a fattier roast. While some cooks may prefer this cut because the fat adds flavor, the more tender and more regularly formed loin end is considered the best.
"Prime" rib is something of a misnomer. Originally used to refer to the most desirable portions of the rib section, the term became somewhat confusing once the U.S. Department of Agriculture began using the label "Prime" as one of its beef-grading classifications. The grades classify the meat according to fat marbling and age--as well as by price. Prime is the best, followed by Choice and Select. Prime-grade prime rib costs about $17 a pound, while Choice-grade prime rib goes for about $13 a pound. Additionally, some butchers offer dry-aged prime rib--Prime-grade rib roasts that have been aged for up to a month to tenderize the meat and concentrate its flavors. Dry-aging adds another $2 to $3 to per pound.
To find out if Prime-grade prime rib is worth the premium, we cooked about $1,500 worth of beef, including several Prime-grade, Choice-grade, and dry-aged rib roasts. In the entire lot, there were no outright losers, but the experiment was telling. First, we don't recommend spending the extra cash on dry-aging. Given the intense flavors imparted by the grill, any distinguishing nuances were lost. On the other hand, in most cases the Prime cuts beat out the Choice cuts in terms of superior marbling and, thus, superior flavor and texture. Given that this meal will be a splurge no matter how you slice it, springing for Prime beef makes sense, although a Choice roast will be almost as good.