All food materials are poor conductors of heat - it takes time for the heat to penetrate.
The correct time and temperature depends on (1) what is to be accomplished, (2) size to thickness, i. e., the extent of surface exposed to the heat, compared to the bulk.
Foods with a large proportion of eggs require low temperature to prevent toughening.
No food containing much water can be raised to a temperature above the boiling point - 212° F. Water gives off vapor at all temperatures, but at 212° F. steam forms rapidly and in so doing absorbs a large quantity of heat. No brown crust can be formed until the water from the surface is nearly all evaporated. A full oven in which much water vapor is being given off requires the application of more heat than when only one or two dishes are in it.
In baking doughs, the larger the mass the lower must be the temperature in order that the heat may have time to penetrate to the interior and expand the gas and harden the albumen and gluten. If the temperature is too high at first, a crust forms, preventing the proper expansion of the loaf and hindering the penetration of the heat.
Thin loaves, pieces of meat, etc., need much less time for cooking, because the heat pentrates quickly. Higher temperatures may be used, as the food is cooked before the surface begins to be burned.
• Mixtures containing much sugar or molasses burn easily.
Vegetables containing much fiber need long boiling to soften them and separate the cellulose. Young, green vegetables contain less fiber and require less time in cooking.
Bearing all the above in mind, the following tables may serve as a general guide for beginners. When it is possible to do so, TEST.