Even though it may appear and smell perfectly fine, cooked food can begin to cultivate dangerous bacteria within as little as an hour if not refrigerated [Food Safety]. Correct reheating is essential for destroying these bacteria. Cooks need to exercise caution not only when reheating foods, but also when heating any dish that contains leftover ingredients, such as soups and casseroles.
The FDA [Food Safety and Inspection Service] (http://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/safe-food-handling/leftovers-and-food-safety/ct_index) advises that dishes should be reheated to 165 degrees Fahrenheit for at least 15 seconds, so an instant-read cook’s thermometer is an essential piece of equipment. The FDA recommends taking at least two readings, one of which should be from the thickest part of the food. Certain foods are more susceptible to dangerous bacteria than others, in particular meats, dairy, sauces containing dairy, and eggs. Rice, pasta and potato are some of the most commonly overlooked, because the innocuously looking foods harbor the dangerous heat-resistant bacillus cereus spore.
The faster you can reheat food to 165 degrees, the better. According to the [National Food Service Management Institute] (http://www.nfsmi.org/documentlibraryfiles/PDF/20130806032737.pdf), no more than two hours should pass to bring food from 41 degrees Fahrenheit to 165 degrees, and food that has not reached 165 degrees within two hours should be discarded. Likewise, cooked food should be cooled as quickly as possible for storage below 40 degrees. The FDA recommends dividing large soups or stews into smaller containers, and slicing up roasts and poultry into smaller parts. If a pan or dish is too hot to go directly into the refrigerator, place it in an ice-water bath first and leave dishes on a shelf where air can circulate rather than on a flat surface. Minimize the spread of bacteria by wrapping or sealing leftovers before refrigeration; the added benefit is that airtight packages keep odors from affecting other foods.
How to Heat
Food can be safely reheated with direct heat on the stovetop or with indirect heat in the oven or microwave. Safely reheat leftovers from a frozen state as long as the overall reheating time does not exceed two hours. Bring frozen sauces, gravies and soups to a rolling boil in a covered pan on the stovetop. Microwaving is usually the quickest method for reheating leftovers, but can result in an uneven penetration of heat. Ensure that microwaved foods are rotated and turned regularly, and covered to retain moisture and build steam. For dishes with a significant variety in density and texture, such as a stew of chicken legs and vegetables, the slow, penetrating heat of an oven eliminates the need to probe for cold spots. Again, cover the dishes to retain moisture.
Some foods do not lend themselves readily to reheating in the microwave or just taste better using other methods. For example, reheat pizza in a covered skillet to melt the cheese and crisp up the dough. To reheat rice on the stovetop, add a splash of water, cover it while cooking and fluff it up afterward to evenly distribute the heat. To safely revive leftover steak or chicken, you may have to sacrifice structure. Chop the meat into smaller pieces and saute it in a hot skillet, for example. Reheat side-dish roasted potatoes by placing them in a single layer on a sheet pan and cooking them in the oven at 400 degrees covered in foil. Uncover them during the last few minutes of cooking.