Why does the frying oil foam up when the food is added to the pan for deep frying?
All foods contain moisture. When even small amounts of moisture on the surface of a food come into contact with hot cooking oil, it foams or boils up somewhat. For safety, never fill deep fryer more than 1/3 full with oil. Make sure food is as dry as possible before adding to hot oil by drying food pieces with paper towels or coating food pieces with flour. Always use tongs or a fry basket to carefully add foods to the oil.