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The Unrivaled Practical Guide for Asian Cooking

Why glass shatters when there is a quick temperature change?

The natural brittleness and poor conductivity of glass make it susceptible to cracking when it experiences a rapid change in temperature from cold to hot or vice versa. Contemplate what happens, for instance, when boiling water is poured into a cold glass jar. Because glass has a low heat-flow efficiency, the heat that is transferred from the water to the jar's bottom travels relatively slowly (by conduction) to the top of the jar. Since glass (or any other material) expands when heated, the jar's bottom will quickly swell, and what is most critical without a corresponding expansion in the upper part of the jar. This disparity creates a structural stress that cracks the doomed glass.

Treated glass, such as Pyrex, is much less vulnerable to shattering than is regular glass, though it, too, has its limits. Even less susceptible is Corningware. Standard porcelain, earthenware, and other pottery, however, do indeed have glass's "Achilles' heel," so it is a good idea to preheat a vessel made with one of these materials (with, for instance, hot tap water) before placing it in a preheated oven.

06:53:08 on 02/27/07 by Webmaster - Questions and Answers -

Why aluminum pot can give a red tomato sauce a brownish tinge?

If an unlined aluminum vessel is used to cook a high-alkali food such as potatoes, or if the cooking medium is hard water, or if the pot is washed with high-alkali cleanser, the metal's surface becomes stained. When the pot is subsequently used to cook tomato sauce or any other high-acid ingredient, such as onions, wine, lemon juice, or cabbage, the acid chemically removes some of the stain from the pot and transfers the discoloration to the food. Although the brownish tinge diminishes the aesthetic appeal of the food, it should pose no threat to your health.

Another drawback of aluminum pots is their propensity to warp when subjected to abrupt changes in temperature extremes (more so than, say, stainless steel of identical gauge). And aluminum implements dent easily, especially if they are thin-gauged.

On the plus side, the heat-flow efficiency of a thick-gauge aluminum pot nearly rivals that of a copper pot of similar gauge, which is noticeably heavier and many times more expensive. Unlike cast iron or carbon steel, aluminum doesn't rust (though it does oxidize slowly). If treated with care, aluminum pots will last for decades.

01:49:26 on 02/27/07 by Webmaster - Questions and Answers -