Starches, like the flour, cornstarch and potatoes, thicken beef stew. Sometimes, beef cubes are coated in flour, then browned, leaving flour in the pan while sealing flour to the meat. When the meat is later simmered, that flour thickens the liquid as do potatoes, which release their starches as they cook. Cornstarch is often stirred with cold water into a slurry that’s then simmered in the cooking liquid to thicken it.
