With cooked fruits and vegetables, undercooked is a matter of taste. With meat, fish and poultry, on the other hand, cooking food until it is completely done has health and safety implications -- about 3,000 Americans die each year from food-related illness, according to Foodsafety.gov, a U.S. Department of Health and Human Services website. Although visual and other sensory clues help determine whether or not foods are cooked thoroughly, those methods only work for some foods.

An instant-read thermometer tells you when food is not yet fully cooked. Some meats, such as pork or chicken, can still look pink and be thoroughly cooked, while others, such as hamburger, may look cooked but not have reached a safe internal temperature. Keep a chart of safe temperatures handy in your kitchen to check that casseroles, ground meat, roasts, chops, steaks and all poultry reach 165 degrees Fahrenheit, and pork, ham and fish reach 145 F.

Two schools of thought exist on vegetables -- some people prefer vegetables crisp-tender, meaning that they've been heated through but are only slightly tender and still have a crunch; others call crisp-tender vegetables undercooked and prefer vegetables roasted or braised in liquid until they are very soft. Crisp-tender vegetables take only 2 to 3 minutes of sauteing or steaming to be done, while vegetables braised in stock or water take 20 to 40 minutes to reach a mellow and sweet stage.

If your baked goods come out gummy in the center and have an unattractive pale appearance instead of a golden brown shade, they are undercooked. Because ovens don't all heat uniformly and because certain spots in your oven may be hotter than other spots, simply following a recipe for time doesn't guarantee that food is completely cooked. Check your oven temperature with an oven thermometer, rotate cookie sheets and cake pans for even cooking and look for an evenly browned exterior to help prevent undercooking.

An oozing and runny egg white clearly indicates that your fried egg is undercooked, but that's not the only thing you need to consider. Unless you're using pasteurized eggs that are completely safe when undercooked, a fried egg is undercooked if the yolk is overly runny. Fried eggs need cooking for 2 to 3 minutes until the yolks have slightly thickened to help ensure that any bacteria dies, according to P.H. Schmutz, a food safety specialist with Clemson Cooperative Extension.