Cold storage is the method of preserving perishable commodities including dairy products in their fresh and wholesome state for extended periods by providing and controlling proper temperature and humidity conditions within the storage compartments. Because normal atmospheric conditions of temperature and humidity are seldom at a level conducive to the safe and prolonged storage of perishable foods, it is necessary that artificial methods be provided to produce such an environment. This safe environment is formed of various favorable conditions of air inside the cold storage given below:
i. Types of Conditions inside a Cold Storage
a) Temperature: The first main condition of air required in a cold storage is ‘Low temperature’. The low temperature retards or arrests most of the spoiling activities like bacterial growth in dairy products.
b) Humidity: It is the moisture content of air in cold room. It is also an important parameter and required to be kept in a certain range. Very low humidity means the product will loose its moisture due to increased evaporation in dry air. Very high humidity means the growth of moulds/ bacteria will take place. However,effect of humidity is lowered down either by packaging the products or by wrapping these with moisture resistant paper.
c) Motion of Air: It means that the cold air should not be stationary but should flow continuously over the products for better heat transfer. It is ensured by suitably designing the cooling coil and blower
d) Purity of Air: It is also an important parameter because impure air may badly affect the quality of food products stored in. Suitable measures are taken to ensure purity of inside air.
In this way the major consideration is made for temperature, humidity, motion and purity of air in a cold storage. But in what range the temperature and humidity should be? That is decided and designed based on some prior considerations as mentioned below:
ii. Prior Considerations in Deciding inside Conditions of a Cold Storage
In actual, cold storage conditions are determined first by the type of food to be stored and second by the length of time such foods are to be stored.
a) Type of Food: In general, types of foods are divided into two groups:
1. Foods in which living process continues, i.e. these absorb oxygen and produce respiration heat. Fruits and vegetables come in this category. The low temperature exposure has only a retarding effect on these foods.
2. Non-living foods such as meat, fish and dairy products that are highly susceptible to the activity of spoilage agents. These products deteriorate rapidly unless the drastic preventive measures of preserving these are taken.
b) Storage Time: Second consideration is the length of time for which dairy products are required to be stored/ preserved. It decides chiefly that the products are to be stored in frozen or unfrozen state. The storage period is less for unfrozen products and longer for frozen products. However, this rule is not so simple because the storage period, even in frozen state, varies considerably from product to product. Freezing temperature also vary for different dairy products.
Thus there is a wide variation of data for storage temperature, relative humidity,freezing point, maximum storage period at different temperature etc. for various types of dairy products. A sampled data is given in Table
i. Types of Conditions inside a Cold Storage
a) Temperature: The first main condition of air required in a cold storage is ‘Low temperature’. The low temperature retards or arrests most of the spoiling activities like bacterial growth in dairy products.
b) Humidity: It is the moisture content of air in cold room. It is also an important parameter and required to be kept in a certain range. Very low humidity means the product will loose its moisture due to increased evaporation in dry air. Very high humidity means the growth of moulds/ bacteria will take place. However,effect of humidity is lowered down either by packaging the products or by wrapping these with moisture resistant paper.
c) Motion of Air: It means that the cold air should not be stationary but should flow continuously over the products for better heat transfer. It is ensured by suitably designing the cooling coil and blower
d) Purity of Air: It is also an important parameter because impure air may badly affect the quality of food products stored in. Suitable measures are taken to ensure purity of inside air.
In this way the major consideration is made for temperature, humidity, motion and purity of air in a cold storage. But in what range the temperature and humidity should be? That is decided and designed based on some prior considerations as mentioned below:
ii. Prior Considerations in Deciding inside Conditions of a Cold Storage
In actual, cold storage conditions are determined first by the type of food to be stored and second by the length of time such foods are to be stored.
a) Type of Food: In general, types of foods are divided into two groups:
1. Foods in which living process continues, i.e. these absorb oxygen and produce respiration heat. Fruits and vegetables come in this category. The low temperature exposure has only a retarding effect on these foods.
2. Non-living foods such as meat, fish and dairy products that are highly susceptible to the activity of spoilage agents. These products deteriorate rapidly unless the drastic preventive measures of preserving these are taken.
b) Storage Time: Second consideration is the length of time for which dairy products are required to be stored/ preserved. It decides chiefly that the products are to be stored in frozen or unfrozen state. The storage period is less for unfrozen products and longer for frozen products. However, this rule is not so simple because the storage period, even in frozen state, varies considerably from product to product. Freezing temperature also vary for different dairy products.
Thus there is a wide variation of data for storage temperature, relative humidity,freezing point, maximum storage period at different temperature etc. for various types of dairy products. A sampled data is given in Table
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| Storage of Dairy Products |
Some dairy products like ice-cream is always stored in frozen condition i.e. at a deep low temperature. Depending upon the available data, the main parameter, i.e.,temperature to be maintained in the cold storage is decided on the basis of type of dairy product and duration of storage.
Depending on the temperature range, the principal refrigeration system employed with cold storage is divided in two groups as ‘chillers’ and ‘freezers’. Chillers maintain a temperature above 0 o C i.e. above the freezing points of products and freezers maintain the temperature below 0 o C, i.e., below the freezing point of products.
Depending on the temperature range, the principal refrigeration system employed with cold storage is divided in two groups as ‘chillers’ and ‘freezers’. Chillers maintain a temperature above 0 o C i.e. above the freezing points of products and freezers maintain the temperature below 0 o C, i.e., below the freezing point of products.
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