Food freezing system

FREEZING METHODS

The freezing of food is the most important thing to preserve the food for a longer period. Industry uses several methods for freezing. The following are a few methods.

1. Blast freezing (Convection)
2. Contact freezing (Conduction)
3. Cryogenic freezing (Convection and/or Convection)
4. Cryomechanical freezing (convection and/or conduction)

Blast freezing (convection)

Cod air circulation is done with the help of fans with high velocity. Product heat is taken by air/refrigerant.

Contact freezing (conduction)

In this method, food directly comes in contact with the cold metal surface. Direction conduction extracts heat through the surface.

Cryogenic freezing (convection and/or conduction)

Liquid nitrogen or liquid carbon dioxide is sprayed into the freezer to bring the temperature down below –60°C.

Cryomechanical freezing (convection and/or conduction)

First cryogenic freezing is done on the food and then finish frozen by mechanical refrigeration.

We will cover Blast freezing in this post.

BLAST FREEZERS

Air is the heat transfer medium in the blast freezer. Airflow is controlled using fans.

Blast freezing is done by several methods like a single compartment or freezer, in cold room, batch freezing, process line freezing, Push through trolley, etc.

Stationary Blast Cell Freezing Tunnels

It is like a cold room. The room is well insulated. Refrigeration coil is and axial of centrifugal fan is provided to circulate the air in the chamber. Most of the products can be freezes using this method. As shown if figure trays are used to place the product. These trays are kept on the racks. Racks are placed in a way that air can be circulated properly all over the product. It's an ideal freezer for all kinds of products.

Push-Through Trolley Freezers

Racks are fitted with castor wheels for easy movement of the racks in the freezer. These racks are moved with help electrical or hydraulic pushing mechanism. This freezer is used to save the labor and handling cost else this freezer is the same as a stationary freezer. This freezer is used for quick-chill (Crust-freeze) for poultry and irregularly shaped packages.

Straight Belt Freezers

Straight belt freezers are having belt conveyor with wire mesh in the blast room. These freezers are used for continuous product flow. These freezers are used for vegetables, fruits, cooked meat.

Two-stage belt freezers

The two-stage freezer is the same as straight belt freezer only difference is, two mesh conveyor belts are used in series. The first belt is used for precooling while the second belt is used for final cooling. The first belt is called a crust-freezer which cools the outer layer or crust and the product is transferred to the second conveyor. The first conveyor normally operates at –9 to –4°C temperature and second at –32 to –40°C temperature.

Multipass Straight Belt Freezers

These freezers are used when longer freezing time is needed like up to 1 hour. The length of the straight belt freezer will be long for such a long time. Also, the floor space required will be too long

. To reduce the length and floor space these multipass straight belt is used. Space is reduced by stacking belts above each other as shown in the figure. 

Spiral Belt Freezers

Spiral belt freezer is also used for a product that requires long freezing time up to 3 hours. The spiral belt provides proper handling of the product during freezing.