Hardening and Storage

Hardening is a continuation of freezing process. Only part of water in ice cream mix is converted into small ice crystals in the ice cream freezer. When ice cream is removed from freezer and put in the packaging materials it has a semi fluid consistency not stiff enough to hold its shape. Therefore freezing process is continued without agitation in a very low temperature room until the temperature of ice cream reaches –18 °C or below, preferably –30°C. This process is called hardening of ice cream.

The refrigerated place where the hardening takes place is called hardening room or hardening chamber or cabinet.

Quick freezing of ice cream during hardening is also desirable. Slow hardening will favour large ice crystals formation in ice cream and hence the texture of ice cream will be coarse. Time required to complete hardening process depends on the following

• Initial composition of mix
• Temperature of ice cream drawn from freezer
• Over run in ice cream
• Size and shape of packages
• Temperature of air in hardening room
• Rate of air circulation in hardening room
• Sections of the hardening room where the ice cream containers are stored.

Hardening time of 6- 8 hr may be considered normal for the operation to be completed. However large containers may take more time as compared to small packages.

1. Hardening Methods: The following hardening methods are used for fast hardening of ice cream:
i) Hardening room: This is a low temperature cold store maintained at – 30 °C or lower with large storing space. Also a good air circulation is maintained throughout the room for uniform cooling effect.

ii) Hardening tunnel: This is a hardening room constructed in the form of an insulated tunnel through which large volume of air is discharged. The air circulated in the tunnel may be at –35 to – 40 °C and this helps in fast hardening of ice cream. Small blast tunnel hardeners may also be located in hardening room for faster hardening. Manufacturers of large volume of
ice cream prefer to have this type of system.

iii) Hardening cabinet: This is a small, refrigerated cabinet maintained at –25 °C or below. It may have two or more compartments separated from each other. Ice cream cups are tightly packed and stored in these compartments. This unit serves as hardening and storing cabinet. This type of unit is useful where volume of operation is low.

2. Storage: After ice cream is hardened it is ready for sale. Until such time it is marketed ice cream should be stored at temperature at which it is hardened.

Hardening rooms or cabinet can be used as storage rooms for ice cream. If separate storage room is used the following precautions should be taken:
i) Room temperature should be maintained uniformly (-11 to –15 °C)
ii) Ice cream packages should be piled very closely
iii) Cold air should be circulated uniformly throughout the room
iv) Frequent opening and closing of the room should be avoided.

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