Before it's divided into primal cuts, and then into subprimals and individual retail cuts, beef starts out as something called a side of beef.
After removing the hide, viscera, head and legs, the beef carcass is split down the middle, right down the backbone, into two symmetrical halves. Each half is a side of beef.
A side of beef can weigh anywhere from 200 to 400 pounds, and it basically features one of everything: one chuck, one loin, one tenderloin, and so on.
Exceptions include items like the tongue, heart, liver and tail (oxtail), of which there are obviously only one each per steer. Hanger steak is another example of this.
Aging Beef: Wet or Dry?
A side of beef needs to be aged before it can be sold at the supermarket or butcher shop, and there are two ways of doing this.
The most common way is called wet-aging. With wet-aging, the side of beef is divided into primals, sub-primals and/or retail cuts, which are vacuum-packed in plastic bags, then boxed and shipped to the retailer. The meat ages in the plastic bags.
Dry-aging involves hanging the side of beef in a climate-controlled refrigerator case where it ages while exposed to the air. In dry-aging, there is considerable moisture loss as the meat's natural juices (i.e. water) drain away.
In both cases, the beef needs to age for anywhere from 14 to 21 days.
Also see: Why You Need to Find a Great Butcher
Dry-aged beef is overall more tender and flavorful, but it's also more expensive. Most of the beef you buy is going to be wet-aged.
Forequarter and Hindquarter of Beef
The side of beef is further divided into two sections, between the 12th and 13th rib. The front section is called the forequarter, and the rear one is the hindquarter.
The forequarter is where we get the chuck, rib, plate and brisket primal cuts. The round, flank and loin primal cuts come from the hindquarter. (The loin is sometimes considered to be two separate primals, the short loin and the sirloin.)
Side of Beef Yield
The yield on a typical side of beef is probably somewhere between 55 and 75 percent. Meaning that anywhere from 25 to 45 percent of it is lost in the form of trim, bone, and fat.
Note that the most desirable steaks, like ones from the short loin, rib and sirloin, make up only about 15 percent of a side of beef. Chuck roasts and round roasts, which are best suited for braising, make up around 35 percent. Another 10 percent goes into things like short ribs, brisket, skirt steak and so on. And the rest ends up as ground beef or stew meat. These yield percentages, as much as anything else, explain why some cuts of beef are so expensive.