Fst 151 food freezing food science and technology 151 Special topics: Freeze Drying

Freeze-drying

• Completely remove water from some material, such as food, while leaving the basic structure and composition of the material intact
• Two reasons
• Keeps food from spoiling for a long period of time
• Significantly reduces the total weight of the food
• How?
• Freeze the material
• Lower the pressure (<0.006 atm)
• Increase the temperature slightly

• Normal (right) and freeze-dried (left) spaghetti

Freeze-drying

• How?
• Freeze the material
• Lower the pressure
• Increase the temperature slightly

• Normal (right) and freeze-dried (left) spaghetti

• A commercial freeze dryer

Methods for transferring heat to the sublimation front

• 1 Heat transfer through the frozen layer
• 2 Heat transfer through the dried layer
• 3 Heating by microwave