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Cryogenic freezing and chilling systems- Uses and benefits
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Friday, 28 May, 2021, 13 : 00 PM [IST]
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Joshna Joseph
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Cryogenic freezing is a type of food preservation technique which involves liquid nitrogen or liquid carbon dioxide or dichlorodifluoromethane as refrigerants at a very low temperature (about -196 degrees C) which helps in rapid removal of heat from the product and forms small ice crystals.
Cryogenic freezing of foods began in the 1960s and around 6% of the foods in the world are cryo frozen. In normal mechanical freezing the refrigerant cools the air surrounding the product which later freezes the product, while cryogenic freezing involves direct freezing of the product by spraying the cold refrigerant on the product.
Cryo freezing leads to the formation of small ice crystals in the product as compared to mechanical freezers. Cryopreservation of food (plants as well as animals) is the only good method of food preservation of food which preserves the fresh food for a longer period of time without affecting the quality of food.
Traditional food preservation by freezing affects the quality of food such as product shrinkage, toughening or loss of tenderness of food, product shelf life, microbial activity, drip loss and dehydration loss. All these are the major concerns in conventional freezing of food which have been overcome by cryo freezing technique. The fluids used for freezing the food material are called cryogens and require special care while handling along with all the safety measures. If cryogens come in contact with skin, it may burn the skin and if it comes in contact with the eyes there will be loss of vision.
There are four types of cryogenic freezers a) Cabinet freezer- It has a lowest temperature of -150 degree Celsius. b) Tunnel freezer- In this type the product is passed through the conveyor inside a tunnel and the liquid refrigerant is sprayed or poured on the product and its lowest temperature is -100 degree Celsius. c) Spraying freezer- In this type the refrigerant usually liquid nitrogen or liquid carbon dioxide is directly sprayed on the food product. d) Immersion freezer- Food product is taken and immersed in a bath container which is filled with the refrigerant via conveyor belt. The unpackaged food product is immersed in the cryogenic liquid.
Chilling is done quickly on raw materials with cryogenic liquid which helps in the reduction of the food safety concerns by stunting the growth of spoilage causing microorganisms. In the food industry, a tunnel freezer is usually used, as the rate of production is not disturbed and goes on continuously.
There are many applications of cryo freezing of food in the food industry. In the dairy sector, the cryogens are directly inserted into the ice cream mixture or sherbet when it is being churned, inducing the cryogen directly into the mixture has proven to stop the spoilage while in storage. Initially, the food product cools quickly below zero degree celsius and slows down till it reaches the critical temperature, after the critical temperature is passed the temperature starts decreasing rapidly. The faster the process the lesser the damage to the product. Commercial application of cryo freezing has been conducted by the developed countries and they have been successful in it. Cryo freezing is also applied in the marine and the meat sectors where the fish and meat are cleaned and cryo frozen and exported.
Preservation of fruits and vegetables and other perishable foods by cryo freezing increases the shelf life of and maintains the quality of the product, where the droplets of the cryogens are inserted inside the packaging material of the food product which evaporates quickly and displaces the air inside the package while making it impossible for the microorganisms to grow in the food.
Cryogenic freezing has gained importance in grinding of spices. Grinding of spices leads to the loss of volatile flavour components of the spices due to the heat generated during grinding, also, the fat content of the spices was also a problem as the grinding would not produce uniform spice powder.
Cryogenic freezing of spices involves injecting the cryogen directly into the grinding mill which inturn freezes the spices and removes the heat from the spices giving a better flavour retention of the spices and does not let the volatile components of the spices to escape. Thus, cryogenic freezing also improves the grinding quality of the spices. Cryogens can also be used for preserving temperature sensitive food during transportation where conventional chilling of the product may not be efficient.
Following are the benefits of cryo freezing:
? The quick freezing of the food product reduces the time and effort.
? The quality of the product is maintained.
? The shelf life of the product is increased.
? The cost of installation and maintenance is low and requires minimum manpower.
? Improves handling of the product.
? Uniform freezing of the product.
? Formation of small ice crystals which reduces the chances of freezer burns.
? Dehydration of the food product is less as compared to the conventional freezing methods and also reduces the oxidative rancidity.
The use of cryogenic freezing in India is still in the developing stage and requires demonstrations and more awareness for this technique to come up in the Indian market. Use of cryogenic freezing will benefit the Indian market in all terms and will also help India to export better quality food products.
(The author is R&D manager at Soch Foods LLP)
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