Freezing and various kinds of it

Table of Contents

The history of freezing

Freezing is one of the methods to preserve food, which keeps the quality of products and it is done by reducing the temperature of the food.

In the distant past, people used methods such as drying and pickling food to make them last longer. Later, they found out that keeping food items underground and in caves, that have a lower temperature, slows down their decomposition. In the 18th century, following the discovery of natural freezers, a mixture of ice and salt was used to freeze food. Finally, in the 19th century, Jacob Perkins invented the cold production method in an industrial way; then, Carl Von Linde, by using ammonia, introduced the cold production cycle to the food industry. Due to the widespread use of refrigerators and freezers in homes and in restaurants, the demand for frozen foods increased.

Today, freezing methods play an important role in food industries all over the world. Freezing seafood products prevents the breakdown of their compounds and the growth of bacteria; therefore, it destroys disease factors.

Freezing seafood products

Seafood is considered as a luxury product in the world. The quality of the final product is so important for producers of marine products. In the marine product classification, one of the most difficult products for managing is shrimp due to its high perishability. In order to obtain high quality products, the improvement of storage methods is considered as the important section. If the freezing is done in a basic and correct way, the product will last for more than one year.

Different freezing methods

Nowadays, different methods are used to freeze food, which are generally divided into two groups, slow freezing and quick freezing.

1. Slow freezing: In this method, the products are placed in a room whose temperature is between -18 to -40 and they are slowly frozen in still air. In this method, the freezing process may last between 3 hours to 3 days.

2. Quick freezing: Quick freezing is one of the methods of freezing food products, which decreases the temperature of the product and freezes it in a very short period of time. This method causes the formation of small ice crystals and cell damage is significantly reduced. There are three types of quick freezing, which are:

a) Freezing through indirect contact: In this method, the product is frozen through indirect contact with the frozen substance that is flowing inside the hollow metal plates. After the initial packaging, the product is placed in the freezer and in the space between the plates. Then, the plates get close to each other and the frozen substance flows inside the plates and the product is frozen.

b) Immersion freezing: In this method, the product is directly immersed in the freezing substance (sodium chloride). Due to the reduction of resistance, there is more contact between the product and the freezing substance and it causes heat transferring to be done in the best way. It is worth nothing that the temperature reduction of the product and its high speed are the advantages of this method, but it may cause the solution to penetrate inside the package. Freezing shrimp by immersion method is generally used in fishing boats.

c)Air blast freezing: In this method, high-speed air blowing and low temperature is used around the product for freezing. The product is placed in a way that the air flows freely through the product.

Based on blowing cold air, two of the most used and newest methods of freezing are examined:

Freezing tunnel: One of the most used technologies, which is part of the quick freezing category and uses the cold air freezing method, is the freezing tunnel. Freezing tunnels are spaces that freeze products by blowing cold air. The temperature of the freezing tunnels reaches -40 degrees Celsius and the freezing rate is high.

Individual quick freezing or single tray freezing is another method of freezing through cold air, and it is considered the newest methods of quick freezing in the food industry, which is widely used in Iran and other countries. This method is very suitable for products that have small dimensions, such as shrimp. In IQF technology, the working method is based on the circulation of extremely cold air that flows around the product by a fan. The products are frozen separately and individually. In the IQF method, the products reach the freezing temperature of about -40 degrees Celsius in a time interval of 3 to 20 minutes. Therefore, short period of time for freezing causes minimal changes in the texture of the product and preserves its taste and nutritional value.

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