3. Microwave defrosting and tempering

Large quantities of food are preserved by freezing, after harvest, for use throughout the year. Food is thawed when the temperature of the product is above 0°C and no trace of ice remains. This is a very important unit operation in the food industry. Tempering is a similar operation, completed when the product temperature is close to – 5 or – 2 °C so that, for example, fish or meat can be sliced for further processing. Tempering can be seen as the initial phase in a complete defrosting stage.

• The most common method of thawing is to apply heat to the surface of frozen foods so that it propagates inwards. However, this process is slow, and food is susceptible to damage from chemical or physical changes, or from the appearance of micro-organisms. To limit this microbial development, the food industry is looking to increasingly rapid systems,...