The first operation on this material usually is to dice, slice or separate individual sections into smaller pieces. Tempering should be done without overheating any part of the product. Thus it produces large temperature gradients, with both under tempering and over tempering in the same block. In conventional tempering, cartons of frozen food in solid blocks weighing up to 100 pounds are raised in temperature to just below freezing.
Most plants dunk the blocks into warm water.
Others use hot air. Many use floor tempering alone, without any heat aid, which may take 48 to 72 hours. Microwave tempering is applied on a moving belt to food still in cartons, and generally takes less than five minutes. Microwave energy is a form of electro-magnetic energy. The electrical power is converted to heat.