One of the best cuts of beef for making beef stew is chuck, and a cut of beef labeled "pot roast" in the grocery store is likely to be chuck. Chuck comes from the well-exercised shoulder and upper foreleg of the steer, so it has lots of tough connective tissue and sinew, a quality that makes it unsuitable for dry-heat, short-cooking methods like grilling and sautéing. But slow, moist, gentle cooking (stewing or braising) transforms the toughness into delectable fork-tenderness and rich flavor.
Not all cuts of chuck are exactly the same. A single chuck contains a complicated network of muscles that can weigh as much as 100 pounds, so it's no surprise that smaller cuts from the chuck will vary greatly. Ground chuck has the maximum fat content allowed by government standards, which makes it especially delicious in burgers.
Choose a cut with the fewest muscles (distinguished by their slightly different grains and dividing lines of fat or gristle). Different muscles cook at different rates, so the fewer the muscles, the more evenly your stew will cook. The best cuts to look for are top blade, chuck eye, and arm pot roast. Also look for thin streaks and small specks of fat—called marbling—running throughout the meat. The fat melts during cooking and bastes the meat internally so it becomes moist and tender. Don't confuse marbling with the thicker strips of fat that separate distinct muscles.