Angelia Butler HSCI 345/Dr. Hughes 23 April 2013 Mini Lecture Outline Chapter 7 I. Microwave Cooking A. Food-Related Uses 1. Home: microwave ovens used most frequently in the home to boil water, heat frozen foods, defrost frozen foods, or make popcorn. a) Speed and convenience b) Younger members of family also use microwave ovens. c) Considered safer for older children than oven. 2. Food Service: Heavy duty commercial microwave units primarily used for reheating. 3. Food Industry: Uses microwave processing largely for meat tempering, bacon precooking, and sausage cooking. a) Equipment used to temper 4 billion pounds of meat a year. b) Tempered by being brought to a temperature just below freezing point of water where they are not frozen but still firm II. Action of Microwaves in Heating A. What are Microwaves? High-frequency electromagnetic waves of radiant energy Radio waves of very short wavelengths Microwaves are generated in a magnetron which converts electric current into electromagnetic energy radiation. FCC assigned certain frequencies: 915 and 2,450 megahertz III. How Do Microwaves Work? A. Intro Microwaves interact electrically with polarized molecules in the food. Polarized molecules (dipolar molecules) act like tiny magnets and align themselves in the microwave electromagnetic field. Heat is produced by friction that is created between rapidly moving molecules. Positive and negative ions of dissolved salts in the food also migrate toward oppositely charged regions of the electric field and generate additional heat by their movement. Within a microwave oven, the microwaves reach the food that is to be cooked both directly from the magnetron unit and indirectly by reflection from the metal walls. A. Safety and Regulation Since 1971, FDA has regulated manufacturing of microwave ovens. Limit of 5 milliwatts of microwave radiation per square centimeter at a distance of 5 centimeters from the oven surfaces. B. Microwave Ovens Designed to function as both a microwave oven and ventilation cooking hood above a range, thus conserving space. IV. Advantages of Microwave Cooking A. Speed of Cooking and Reheating Foods Cooking is ten times faster than with conventional methods. Reheats precooked foods more rapidly and avoid reheated or warmed over flavor. B. Reduction in Nutrient Loss Microwave blanching of vegetables compared to blanching in water resulted in less nutrient loss. C. Energy Conservation Can cook up to about six servings at one time. Do not contribute to the warmth in the home during the hot seasons of the year. V. Limitations of Microwave Cooking A. Surface Browning of Foods Foods that require cooking for a relatively long time would be greatly overcooked before browning would occur. Due to cool air temperature inside the microwave oven and to the cooling effects of moisture evaporation at the surface of foods cooked with microwaves. B. Other Quality Limitations Dried pasta and rice do not cooks more quickly in the microwave oven because rehydration must occur. Sauces and meats do not have an opportunity to develop in the short cooking periods. Bread reheated often becomes tougher. Hydrocolloids (such as xanthan gum) These and microcrystalline cellulose which have water binding capabilities help stabilize many microwavable products and prevent dry spots. C. Overcooking Superheated water Slight movement or addition of instant coffee may cause severe burns or violent eruptions. D. Unevenness of Heating and Food Safety Lack of uniformity in heat distribution Hot and cold spots May not destroy Salmonella organisms in chicken or Trichinella spiralis. Check final temperature of food in several locations of the product. Voltage being fed in microwave must be consistent at all times that the oven is operating. VI. Packaging Materials and Cooking Utensils A. Microwave Usable Dishes Use microwave safe plastic, ceramic and glass containers. Metal or glass containers are generally not acceptable for microwave use. In some products packaging is already provided when purchased. Protects the product in storage and distribution, controls heating of product. Functions as a serving dish and helps to sell product. VII. General Cooking Suggestions A. Browning Smaller quantities of food cooked for short periods must be browned using other methods other than microwave oven. Optimum time for cooking should not be extended to increase likelihood of browning. B. Stirring and Turning Power is unevenly distributed so foods must be turned around, stirred, relocated. Most come equipped with rotating turntable that distributes power. C. Standing Time Food continues to cook several minutes after it’s removed from microwave oven. Heat continues to be conducted from hotter parts of food to cooler ones. D. Defrosting Heat produced in food is distributed throughout. Ground meat, stew meat, whole poultry, or whole fish should be turned. Break apart and separate in over while defrosting is completed. E. Combining Microwave and Conventional Cooking Foods can be cooked efficiently if cooked partly by microwave and partly by conventional methods. For example, bread can be toasted conventionally and fillings can be prepared using microwave. F. Heating Meals Dielectric (and thermal) properties Since different foods have properties, uneven heating may occur in meals with several different components. Temperatures at edge of plate or tray of food tend to be higher than in the center. The edge of the food seems to act as an antenna in the microwave field, absorbing energy.