Introduction:

Cold storage, a crucial link in the global food and catering industries, provides storage facilities with high refrigeration capabilities. It plays an indispensable role in preserving perishable items, such as meat, fish, vegetables, and fruits, by maintaining low temperatures. The demand for cold storage facilities has surged as the food and catering industries increasingly rely on warehouse logistics. In this article, we will delve into the functions of cold storage, its classification based on operations, the specific items it stores, the machinery required, storage procedures, and the requirements for Controlled Atmosphere (CA) cold stores.

Functions of Cold Storage

1. Protecting Perishable Food:

Perishable food items like fish, meat, and dairy products are prone to decay at room temperature. Modern industries combat this by utilizing blast freezers for the storage of meat and fish. Logistics companies store perishable items in refrigerators with high storage capacity before delivering them to the final consumers.

2. Protecting Perishable Nutrient Products
Certain nutrient items, such as cold-blooded aquatic vertebrates and the flesh of animals, can become radioactive when exposed to room temperature. Cold storage warehouse logistics now provide blast freezers for products like these, ensuring their safety and quality.

3. Storage of Dairy Products
In addition to food items, dairy products also require specialized care in cold storage. The equipment for storing dairy products must have precise temperature control to maintain their quality.

4. Storage of Food & Vegetables
While fruits and vegetables need a certain kind of cold storage, they do not necessarily need to be frozen. They benefit from being kept at cool temperatures to extend their shelf life without compromising quality.

Classification of Cold Storage Based on Operation:

Bulk Cold Stores: Primarily designed for the storage of a single commodity and often operate on a seasonal basis, e.g., for potatoes, chillies, and apples.
Multipurpose Cold Stores: These facilities are designed for the year-round storage of a variety of commodities. Products stored in these types of cold stores include fruits, vegetables, dry fruits, spices, pulses, and milk products. They are strategically located near consumption centres.
Small Cold Stores: Equipped with precooling facilities, these are mainly used for export-oriented items like grapes. Initially concentrated in Maharashtra, these units are now gaining popularity in other states like Karnataka, Andhra, and Gujarat.
Frozen Food Stores: Equipped with or without processing and freezing facilities, these stores cater to fish, meat, poultry, dairy products, and processed fruits and vegetables. They have played a significant role in promoting the growth of the frozen foods sector, both domestically and in export markets.
Mini Units / Walk-in Cold Stores: Conveniently located at hotels, restaurants, malls, and supermarkets to meet immediate storage needs.
Controlled Atmosphere (CA) Cold Storage: Specifically designed for certain fruits and vegetables like apples, pears, and cherries. These stores utilize sensors, refrigeration plants, gas diffusers, humidifiers, and conditioning chambers to maintain optimal storage conditions.
Ripening Chambers: Primarily set up for bananas and mangoes to control the ripening process.
The controlled atmosphere cold storage employs a combination of sensors, refrigeration plants, gas diffusers, humidifiers, and conditioning chambers to maintain the storage environment at optimal conditions, minimizing the decay rate of perishable items.
Storage Items for CA Cold Storage
Cold storage is particularly suitable for items with considerable water content, including:
Fruits: Cherry, pears, orange, sweet lime, apple, etc.
Vegetables: Cauliflower, broccoli, cabbage, beans, etc.
Machinery Required
Multi-Stage Compressor: Devices that increase the pressure of a gaseous fluid through more than one compression cycle.
Condenser: A device transferring heat from the working fluid to the surrounding or coolant to cool the working fluid and condense it to a liquid state.
Expansion Valve: A device used for free expansion processes, often used in refrigeration devices after the condenser unit to convert the sensible heat of refrigerant into latent heat, further reducing the refrigerant's temperature.
Evaporator Unit: A device that extracts heat from the fluid medium of a conditioned space by utilizing cold refrigerant running through it.
Cooling Tower: A device that cools water by allowing it to fall through airflow, achieving evaporative cooling.
Humidifier: A device used to increase the humidity of a confined space by utilizing a fogger arrangement as needed.
Dehumidifier: A device used to decrease the humidity of a confined space by utilizing its cooling coil, condensing and draining water from the air.
Oxygen Scrubber: A device that removes oxygen from a given gaseous mixture.
Carbon Dioxide Scrubber: A device that removes carbon dioxide from a given gaseous mixture.
Nitrogen Scrubber: A device that removes nitrogen from a given gaseous mixture.
Nitrogen Generator: A device that generates gaseous nitrogen using an appropriate chemical reaction.
Oxygen Generator: A device that generates gaseous oxygen using an appropriate chemical reaction.
CA Cold Chamber: An appropriately insulated and isolated chamber designed to minimize heat and mass transfer across its boundaries.
Water Pumping Station: Composed of a large number of water pumps supplying water to various facilities within an installation.

Storage Procedure for CA Cold Storage
CA Cold Storage typically consists of multiple chambers, each with a capacity of 50-250 MT. Economically viable designs of small CA Cold Storage with a single chamber and a storage capacity of around 50 MT are anticipated in the near future. Produce is stored in large bins that are stackable up to 11 high, or in PVC crates that can be stacked in mild steel pallet frames up to 4 levels high. Refrigeration systems are designed to maintain a temperature of -1ºC with a humidity of 90%-95% RH. O2 and CO2 levels are automatically regulated, measured, and corrected during the storage period to ensure the highest quality. Automatic regulation is recommended to minimize the possibility of storage disorders in high-value produce stored in CA Cold Storage.
Requirements for CA Cold Store
Pre-cooling/Rapid Cooling: Controlling the temperature of fresh produce and reducing the time the product spends at less than optimal storage temperature are crucial for preserving quality. Different cooling methods such as room cool, hydro cool, forced air cooling, evaporative forced air cooling, and ice packaging may have varying pre-cooling requirements based on the produce. General recommendations for pre-cooling systems should be followed, with the goal of achieving a 7/8 cool for fruits and vegetables.
For example, apples should be cooled as quickly as possible after harvest. A delay of 1 day at 21°C after harvest takes 7 to 10 days off the potential storage life at 0°C. Adequate refrigeration capacity is essential during room cooling to handle the maximum heat load. Proper refrigeration, air circulation, and stacking of bins are crucial for efficient cooling.
Quality of Produce: The storage life of produce depends on its quality at the time of harvest and its preservation during post-harvest. For example, apples stored in controlled atmosphere cold stores worldwide should be harvested when mature but fully ripe for maximum storage life. Immature apples have poor eating quality and are more susceptible to storage disorders.
Therefore, good keeping quality of fresh produce to be stored must be not only sound at the right stage of maturity but also carefully handled in all operations, including picking, grading, and packaging. Rough handling or delays in pre-cooling to recommended storage conditions are primary causes of rotten fruits in storage.
Commodity Storage Conditions: Designing a cold storage facility requires defining product storage conditions, including critical temperature, relative humidity, presence of CO2, ethylene, air circulation, and light. In the absence of research data for Indian conditions, adopting commodity storage conditions as prescribed by the Commodity Storage Manual of WFLO (World Food Logistics Organization) is recommended.
 

Temperature and Humidity Range:

The temperature in the CA cold store facility should be kept within +10ºC of the recommended temperature of the produce being stored. A narrow temperature range may be needed for storing at temperatures close to the freezing point of the commodity.
Humidity: The Relative Humidity (RH) in a long-term CA cold store facility should be kept at 90% to 95%. The refrigeration system must be specially designed to maintain high RH. Cooling coils with large surface areas and refrigerant controls maintain the highest possible coil temperature, reducing moisture loss from the CA cold store air and the produce. Smaller coils result in unacceptable moisture loss and may require supplementation with humidification equipment.
CO2 and O2 levels: As per WFLO commodity storage recommendations, CO2 and O2 levels should be regulated to ensure optimal storage conditions for the produce.
Loading Rate: To achieve good storage quality, the room should be small enough to be filled in 3 days or sooner, with loading rates varying from 3% to 5% of the total cold store capacity. This is critical for sizing the chamber capacity of the Controlled Atmosphere Cold Store.

Air Circulation: A CA cold store should be designed to provide an airflow of 165 m3/h per MT of product, based on the maximum amount of product that can be stored in each chamber. Rapid cooling of the produce is essential. The system should be designed to reduce airflow after the product has reached the storage temperature, achieved through a variable frequency drive and control system. Once the core temperature is reached, airflow should be minimized automatically.
Stacking: Proper stacking of bins or PVC crates is crucial for effective air circulation and ensuring uniform cooling of the stored produce. Well-ventilated bins/crates with vent alignment speed up the cooling rate by allowing the cooling air to flow uniformly.

Lighting Condition: It is recommended to maintain dark conditions during storage to preserve the quality of the produce.

Conclusion
The cold storage business is an integral and evolving part of the global food supply chain. As the demand for storage facilities continues to rise, especially with the increasing reliance on warehouse logistics, it is essential for businesses to adopt best practices and adhere to recommended standards. The advancements in technology, coupled with a commitment to maintaining optimal storage conditions, will ensure the continued success and efficiency of cold storage facilities. By understanding the functions, classifications, storage procedures, and specific requirements, stakeholders in the cold storage business can contribute to a more reliable and sustainable global food supply.