Information AboutBoiling |
| CATEGORIES ABOUT BOILING | |
| cooking techniques | |
| phase changes | |
|
''Nucleate boiling'' is characterized by the incipience and growth of bubbles on a heated surface, which rise from discrete points on a surface, whose temperature is only slightly above the liquid’s saturation temperature. In general, the number of Nucleation sites are increased by an increasing surface temperature. An irregular surface of the boiling vessel (i.e. increased surface roughness) can create additional nucleation sites, while an exceptionally smooth surface, such as glass, lends itself to Superheating . Under special conditions, a heated liquid may show Boiling Delay when heated over its boiling point, by starting to boil suddenly and violently. When the surface temperature reaches a maximum value, the critical superheat, Vapor begins to form faster than liquid can reach the surface. Thus, the heated surface suddenly becomes covered with a vapor layer. Because of the vapor layer’s lower Thermal Conductivity , this vapor layer insulates the surface. This condition of a vapor film insulating the surface from the liquid characterizes ''film boiling''. ''Transition boiling'' may be defined as the unstable boiling, which occurs at surface temperatures between the maximum attainable in nucleate and the minimum attainable in film boiling. The formation of Bubbles in a heated liquid is a complex physical process which often involves Cavitation and acoustic effects, such as the broad-spectrum hiss one hears in a kettle not yet heated to the point where bubbles roil the surface. BOILING IN COOKERY In cookery, boiling is Cooking food in boiling Water , or other water-based liquid such as Stock or Milk . Simmering is gentle boiling, while in Poaching the cooking liquid moves but scarcely bubbles. In places where the available Water Supply is contaminated with disease-causing Bacteria , boiling water and allowing it to cool before drinking it is a valuable health measure. Boiling water for a few minutes kills most bacteria, Amoeba , and other microbial Pathogen s. It thus can help prevent Cholera , Dysentery , and other diseases caused by Microorganism s. The temperature of a substance is constant as it undergoes a raises the temperature of the contents above the open air boiling point. Adding a water Soluble substance, such as Salt or Sugar also increases the boiling point. This is called Boiling-point Elevation . However, the effect is very small, and the boiling point will be increased by an insignificant amount. On the other hand, salt or Ethylene Glycol can cause significant Freezing Point Depression . Due to variations in composition and pressure, the boiling point of water is almost never exactly 212 F / 100 C, but rather close enough for cooking. Foods suitable for boiling include:
Advantages:
Disadvantages:
Boiling can be done in two ways: The food can be placed into already rapidly boiling water and left to cook, the heat can be turned down and the food can be simmered; or the food can also be placed into the pot, and cold water may be added to the pot. This may then be boiled until the food is satisfactory. Water on the outside of a pot, i.e. a wet pot, actually increases the time it takes the pot of water to boil. The pot will heat at a normal rate once all excess water on the outside of the pot evaporates. BOILING FOR WATER PURIFICATION Boiling is used as a method of Water Purification . Boiling is commonly advocated as an emergency water treatment method, or as a method of Portable Water Purification in rural or wilderness settings without access to a potable water infrastructure. BOILING AS A MEANS OF EXECUTION See Boiling To Death . SEE ALSO |
|
|