Introduction
Cold storage is a facility where temperature and humidity are controlled to preserve perishable products such as fruits, vegetables, dairy products, meat, seafood, pharmaceuticals, and other sensitive commodities. The main objective of cold storage is to extend the shelf life, reduce spoilage, and maintain quality of the stored goods.
India, being an agricultural country, produces large quantities of fruits, vegetables, and milk. However, due to inadequate cold storage infrastructure, a significant portion gets wasted. Therefore, cold storages play a vital role in post-harvest management and food security.
Basic Principle of Cold Storage
The fundamental principle of cold storage is based on the concept of heat transfer and refrigeration. It involves the removal of heat from the storage space and maintaining a low temperature to slow down the biochemical and microbial activity of perishable products.
How it Works
- All materials and food items emit heat. To prevent spoilage, this heat must be continuously removed.
- A refrigeration system extracts this heat and releases it outside the storage chamber.
- The temperature inside the cold room is maintained at a desired level, typically between 0°C to 10°C, depending on the product.
- In some cases, freezing temperatures (below 0°C) are maintained for meat or ice cream storage.
Main Components of a Cold Storage
A modern cold storage facility consists of several components designed to work together efficiently:
1. Refrigeration System
This is the heart of the cold storage. It includes:
- Compressor: Compresses the refrigerant gas and circulates it through the system.
- Condenser: Releases the heat extracted from the cold room to the outside air.
- Expansion Valve: Reduces the pressure and temperature of the refrigerant before it enters the evaporator.
- Evaporator Coil: Absorbs heat from the storage area; cool air is circulated using fans.
Refrigerants commonly used include ammonia (NH₃), R-134a, or R-404a.
2. Cold Room Chamber
- Insulated enclosure where goods are stored.
- Constructed using PUF (Polyurethane Foam) insulated panels for thermal efficiency.
- Doors are air-tight and often fitted with automatic closing systems.
3. Insulation
- Prevents heat entry from outside and helps maintain uniform internal temperature.
- Common insulation materials: PUF, EPS (Expanded Polystyrene), XPS.
- Thickness of insulation varies between 60 mm to 150 mm depending on the temperature requirements.
4. Control System
- Includes temperature sensors, thermostats, humidity controllers, and alarm systems.
- Automatic control panels are used to monitor and regulate conditions.
5. Air Circulation System
- Fans are installed to ensure uniform distribution of cool air.
- Prevents formation of hot spots and maintains consistent temperature throughout.
6. Humidification/Dehumidification Unit
- Maintains proper relative humidity (RH), especially for fruits and vegetables.
- For example, apples require 90% to 95% RH while onions need 65% to 70% RH.
7. Power Backup System
- Essential in India due to frequent power cuts.
- Diesel generators and UPS systems ensure uninterrupted cooling.
8. Racking and Material Handling System
- Storage racks and pallets help in organizing materials.
- Forklifts or trolleys are used to move goods efficiently inside the chamber.
Considerations in Deciding Inside Conditions of a Cold Storage
Different products require different temperature and humidity conditions. Below are the key factors to consider:
1. Type of Product to be Stored
Each commodity has specific storage requirements:
| Commodity | Temperature (°C) | Relative Humidity (%) |
|---|---|---|
| Apples | 0 to 2 | 90 to 95 |
| Bananas | 13 to 15 | 85 to 90 |
| Milk & Dairy | 2 to 5 | 85 to 90 |
| Meat & Poultry | -2 to -5 | 85 to 90 |
| Ice Cream | -18 to -20 | Not critical |
| Onions & Garlic | 0 to 2 | 65 to 70 |
| Pharmaceuticals | 2 to 8 | Controlled environment |
2. Storage Duration
- Products like green leafy vegetables are stored for a few days, while apples or potatoes can be stored for several months.
- Longer duration storage may require modified atmosphere packaging (MAP) or controlled atmosphere (CA) chambers.
3. Temperature Sensitivity
- Some fruits like mangoes and bananas are sensitive to chilling and should not be stored below 10°C.
- Conversely, products like ice cream or vaccines require deep freezing below -20°C.
4. Humidity Requirements
- High humidity prevents dehydration in most fruits and vegetables.
- However, for products like onions or garlic, low humidity is essential to avoid fungal growth.
5. Product Load and Volume
- Size of the chamber and refrigeration capacity must be calculated based on volume and turnover of goods.
- Overloading can reduce airflow and affect cooling efficiency.
6. Packaging Material
- Perforated crates or boxes allow better airflow than plastic bags or sealed containers.
- Selection of correct packaging affects cooling and humidity regulation.
7. Hygiene and Sanitation
- Inside conditions should allow for regular cleaning and pest control.
- Drainage, lighting, and anti-bacterial coatings are additional factors.
8. Energy Efficiency
- Better insulation, use of LED lighting, and energy-efficient compressors reduce power costs.
- In India, cold storage operators benefit from schemes and subsidies offered by National Horticulture Board (NHB) and Ministry of Food Processing Industries (MoFPI).
Conclusion
Cold storage plays a crucial role in India’s agricultural and food supply chain by reducing wastage and preserving quality. The basic principle involves heat removal using a refrigeration system and insulated environment. Proper selection of equipment and understanding the requirements of various products help in deciding internal temperature, humidity, and airflow conditions. Well-maintained cold storage ensures better profitability, product safety, and market access, both domestic and international.