1403 331 Food Processes Engineering

1. 1403 331 Food Processes Engineering Food Freezing by Weera Awikunprasert Food Technology Program Mae Fah Luang University

2. 2 Objectives 1. To understand the principle and method of food freezing. 2. To know the freezing system. 3. To predict the freezing time of food.

3. 3 Studying Topics • Introduction • Freezing System • Frozen-Food Properties • Freezing Time Prediction

4. 4 Introduction Preservation of a food by freezing occurs by several mechanisms. Reduction of the product temperature to levels below 0oC. - reduce growth rate of microorganism - correspond deterioration of the product due to microbial activity

5. 5 Introduction Product temperature, Ti Freezer, Ta Product temperature, TF< 0oC water Product temperature, Tf ice

6. 6 Freezing System The freezing process • Indirect contact freezing system : the product and refrigerant are separated by a barrier throughout the freezing process. F8.1 Fig.1 Schematic diagram of an indirect contact freezing system.

7. 7 Freezing System The freezing process • Direct contact freezing system : the product and refrigerant are direct contacted in freezing process. F8.6 Fig.2 Schematic diagram of a direct contact freezing system.

8. 8 Freezing System Indirect contact freezing system • Plate freezers (Fig.3) • Air-blast freezers (Fig.4) • Freezers for liquid foods

9. 9 Freezing System F8.2 Fig.3 Schematic illustration of a plate freezing system.

10. 10 Freezing System F8.4 Fig.4 Continuous air-blast freezing system.