Cold Storage for Apples and How Does It Work

Apple Varieties in India

Some of the important varieties cultivated in India include the following.

How to Store Apples: Everything You Need to Know About Cold Storage

Let us understand the step-by-step storage process in brief.

#1 Pre-Cooling

The requirements for pre-cooling or rapid cooling depend on the produce and method of cooling such as room cool, hydro cool, forced air cooling, evaporative forced air cooling and ice packaging. After harvesting, the apples must be immediately placed in a cool and ventilated place to remove field heat before packing. It is important to remove dirt and moisture from the fruit surface before grading and packing in cartons.

Apples are usually not injured by rapid cooling. A delay of 1 day in the orchard at 21°C after harvest may shorten the storage life by 7 to 10 days at 0°C. Whereas, a delay of 3 days in the orchard or in a warm packing shed may shorten the storage by 30 days, even if they are subsequently stored in a controlled atmosphere at -1°C.

#2 Grading

Grading is done on the basis of the size and appearance of the fruit. divided into six grades based on the size. Depending on the fruit’s colour, shape, quality and appearance, apples can be graded in different quality grades such as s AAA, AA and A; A, B, C; or extra fancy, fancy class I and fancy class II.

#3 Prestorage Treatment

In some cases, orchard-run apples are treated with diphenylamine to prevent storage scald. If packed boxes or cartons are used, then they should have this treatment if the variety is susceptible to scald.

Also, some varieties, such as Golden Delicious, are prone to water loss and that is why fruit boxes or bulk bins can be covered with polyethylene film. It is advised that the covers should not be sealed because the apples may develop an off flavour.

#4 Cold Storage

Controlled atmosphere (CA) storage help maintain desired oxygen and carbon dioxide levels which help slow down the ripening process, prevent some storage disorders (scald in apples) and also minimise the growth of decay organisms. This prolongs the shelf-life of the perishables when compared to regular refrigerated stores and that is why CA storage facilities are recommended for the long-term storage of apples, kiwis, pears, cabbages, etc. for up to 10 months.

Storage Conditions

• Temperature: Most varieties of apples are best stored between 30 and 32°F (-1.8 and 0°C). However, some apple varieties are cold-sensitive and prone to internal browning of the skin and are therefore stored at 38 to 40°F (3.3 to 4.4°C).
• Relative humidity (RH): It is also a crucial part of storage conditions post-harvest. At the time of harvest, apples have around 84% moisture content. To maintain this water content and to avoid shrivelling of the skin, humidity levels should be maintained at >90%. With air circulation, higher RH levels (95 to 98%) can be maintained without the formation of mold.
• Freezing point: Different varieties of apples have varying freezing points. For most varieties, it is below 29°F (-1.7°C). Freezing can cause discolouring of the surface and internal browning. That is why it is recommended to not handle apples when frozen to avoid injury.
• Lighting: Dark storage conditions.
• Oxygen and carbon dioxide levels: It varies depending on the recommendations outlined in WLFO.
• Air circulation: CA cold store should provide an airflow of 165 cmh per MT of product based on the maximum amount of product stored.

Storage Duration

During storage, the quality of apples depends on the fruit maturity at the time of harvesting, delay before cold storage, storage temperature, and the presence of other items in the room. For instance, apples can absorb the odour from celery, cabbage, carrots, potatoes and onions and are therefore not stored in the same room. Moreover, meat, egg, and dairy products can absorb odour from apples and should not be stored together.

Storage duration also depends on the variety. McIntosh ripens quickly at 32°F (0°C) and has a short storage life whereas Rome ripens slowly at 32°F (0°C) and can be stored for longer. Susceptibility to diseases and disorders can also shorten the storage duration. Climatic conditions, handling, and even the orchard culture can have an impact on storage life.

Building a Cold Storage

Here are some key features of a typical layout of CA cold stores.

• CA cold stores usually have multiple chambers each with a capacity of 50 MT to 250 MT including anti rooms, docking area, grading/sorting area, grading/sorting line, bins/palletized storage system and material handling system, etc.
• These stores are usually single-storeyed with individual rooms. The height should be enough to allow fruits to be stacked up to 11 bins high.
• Construction is usually done using steel construction or pre-engineered construction conforming to the required BIS Codes.
• The walls ceiling and partition are generally constructed from insulated composite structural panels which have core insulation of polyurethane.
• RCC slabs or truss roofs with G.S or pre-coated G.S. sheet cover can be used for roofing.
• It is important to ensure the sealing of all joints for maintaining gas-tight enclosures.
• Bins, pallets or rack systems should be provided in CA cold stores.
• Strip curtains are commonly used for reducing the infiltration of air during loading and unloading.
• In terms of equipment, vapour compression systems are commonly used for refrigeration. Ammonia seems to be the most suitable refrigerant as it is eco-friendly, energy efficient, and safe. The compressor can be reciprocating or screw type with capacity control. The condenser can be atmospheric, evaporative, water-cooled, or air-cooled in the case of HFC. A humidification system is installed for maintaining humidity levels.

Final Words

Cold storage for apples is an essential part of post-harvest management. With the right storage conditions and CA cold storage facilities, farmers and producers can not only reap maximum profits but also ensure customer satisfaction with quality produce.

Rinac, an industry-leading provider of cold storage solutions has developed world-class cold storage and controlled atmosphere facilities to help small and big businesses reduce wastage and improve profit margins! To know more about our cold storage solutions and how we can help you, get in touch with us today!