Heating and equipments Dr Fatimah Yousef Heating foods

+ Heating and equipments Dr. Fatimah Yousef

+Heating foods n Heat is the “energy that is produced by the rapid movement of molecules”. n The molecules always have some motion: n Heat speeds up that motion. n Cold temperatures slow it down. n Freezing and boiling are extremes of the range in temperatures encountered in food preparation that owe their effects to changes in this kinetic energy of molecules. n kinetic energy is associated with motion Dr. Fatimah Youaef 12013 Lmia Sindi , MS

+ Measuring heat: n Temperature scales n Thermometers n Calories (Calorie) Dr. Fatimah Youaef 1 Lmia Sindi , MS

+ Measuring heat cont’d n Temperature scales n The three main scales used to measure heat: n Fahrenheit (°F) n Centigrade (°C) n Kelvin (°K) used in scientific research n Freezing point of water: n 32°on °F scales and 0° on °C scales n Boiling point of water: n 212° on °F scales and 100° on °C scales n Other points materials have their own freezing and boiling Dr. Fatimah Youaef 1 Lmia Sindi , MS

+ The three main scales used to measure heat intensity

+ Types of heat transfer n Conduction n Convection n Radiation Dr. Fatimah Youaef 1 Lmia Sindi , MS

+ n. Conduction: n“The direct transfer of heat from one substance to another that it is contacting”. n. The material and size of the pan greatly affect the speed and efficiency of heat transfer n. For instance, the water in a pot boils when the flame from the stovetop heats the pan, and the heat from the pan is transferred to the water via conduction. Dr. Fatimah Youaef Lmia Sindi , MS

+ n. Convection: n “The transfer of heat by moving air or liquid (water/fat) currents through and/or around”. n It is based on the principle that: Heated air or liquid expands, becomes less dense and rises to the surface. The cooler, heavier air or liquid originally on top moves to the bottom, where it is heated thus creating continuous circular currents n The rate of heat flow will depend on the temperature of the moving gas or liquid and on its rate of flow. As fluid motion goes more quickly the convective heat transfer increases. n Baking an oven is an example for convection. Dr. Fatimah Youaef Lmia Sindi , MS

+ Radiation: n “The transfer of heat energy in the form of waves of particles moving outward from their source”. n Heat is transferred by radiation in broiling, grilling, and microwaving. n The short electromagnetic waves that are generated by microwave ovens can pass through glass, paper, and most plastic. Dr. Fatimah Youaef Lmia Sindi , MS