On food and cooking the science and lore of the kitchen ( PDFDrive ) 1467

Forms of Heat Transfer Cooking can be defined in a general way as the transformation of raw foods into something different Most often, we transform foods by heating them — by transferring energy from a heat source into the foods, so that the food molecules move faster and faster, collide harder and harder, and react to form new structures and flavors Our various cooking methods — boiling, broiling, baking, frying, and so on — achieve their various effects by employing very different materials as the medium through which the heat moves, and by drawing on different forms of heat transfer There are three ways to transfer heat, and an acquaintance with them will help us understand how particular cooking techniques affect foods the way they do Conduction: Direct Contact When thermal energy is exchanged from one particle to a nearby one by means of a collision or a movement that induces movement (for example, through electrical attraction or repulsion), the process is called conduction Though it’s the most straightforward means of heat transfer in matter, conduction takes different forms in different materials For example, metals are usually good conductors of heat because, while their atoms are fixed in a lattice-like structure, some of their electrons are very loosely held and tend to form a free-moving “fluid” or “gas” in the solid that can carry energy from one region to another This same electron mobility makes metals good electrical conductors But in nonmetallic solids like ceramics, conduction is more mysterious It seems that heat is propagated not by the movement of energetic electrons — in solids of ionic-or covalent-bonded compounds, the electrons are not free to move ...When thermal energy is exchanged from one particle to a nearby one by means of a collision or a movement that induces movement (for example, through electrical attraction or repulsion), the process is called... attraction or repulsion), the process is called conduction Though it’s the most straightforward means of heat transfer in matter, conduction takes different forms in different materials For example, metals are usually good conductors of heat because,... mysterious It seems that heat is propagated not by the movement of energetic electrons — in solids of ionic-or covalent-bonded compounds, the electrons are not free to move