Freezing Technology

3.5.1.1. Freezing time

Following are the Variables which affect freezing time

1. Freezer type
2. Freezer operating temperature
3. Refrigeration system and operating condition
4. Air speed in an air blast freezer
5. Product temperature
6. Product thickness
7. Product shape
8. Product contact area and density
9. Product packaging
10. Species of fish

Freezer type: The type of freezer will greatly influence the freezing time. For example, due to improved surface heat transfer, a product will normally freeze faster in an immersion freezer than in an air blast freezer operating at the same temperature.

Operating temperature: The colder the freezer, the faster the fish will freeze.

Air speed in blast freezers: Freezing time is reduced as the air speed increased.

Product before freezing: The warmer the product, the longer it will take to freeze. Fish should therefore be kept chilled (+4^oC) before freezing both to maintain quality and reduce freezing time and refrigeration requirement.

Product thickness: The thicker the product, the longer is the freezing time.

Product shape: The shape of a fish or package can have a considerable effect on its freezing time and this is dependent on the ratio of surface area to volume.

Product contact area and density In a plate freezer, poor contact between product and plate results in increased freezing time.

Product packaging: The method of wrapping and the type and thickness of the wrapping material can greatly influence the freezing time of a product. Air trapped between wrapper and product has a greater influence on the freezing time than the resistance of the wrapping material itself.

Species of fish The higher the oil content of the fish the lower is the water content. Most of the heat extracted during freezing is to change the water to ice; therefore, if there is less water, then less heat will require to be extracted to freeze the fish. Correspondingly freezing time will be less.