To scald milk means heating it to just below the boiling point. Use a thick-bottomed saucepan or a double boiler to prevent scorching the milk. Scalding has two primary purposes: to kill pathogenic microorganisms and to destroy certain enzymes that would keep emulsifying agents in the milk from doing their thickening job. Since those two goals are accomplished when milk is pasteurized at the dairy, scalding need only be done when you use raw (unpasteurized) milk. Some cookbook writers do not know this fact and therefore direct their readers to scald the milk even though it is usually unnecessary today.
** Asian Recipes