Many supermarkets have started adding numbered ratio codes to the different grades of ground beef. Along with the titles "Ground Chuck" or "Ground Sirloin" you may see a number like "80/20" or "90/10." This is simply a "lean/fat" ratio (for example 80/20 means the meat is produced using 80% lean and 20% fat). This is actually more accurate because Ground Chuck is seldom produced using only Chuck roasts. Keep in mind that leaner is not always better for all recipes. A burger made with 90/10-ground chuck can be dry and flavorless.