Introduction to Specialized Cold Storage for Fruit Storage

Pome fruits have thick peels, moderate water content, gentle respiration and strong storage resistance, but are prone to browning, softening of pulp and fading of flavor. The core of storage is "low temperature and constant temperature, low humidity and moisture retention, and moderate controlled atmosphere" to inhibit respiration and microbial reproduction.

•  Apples (Red Fuji, Gala, etc.)

The optimal storage temperature is -1℃ to 1℃, the relative humidity (RH) is controlled at 85%-90%, and controlled atmosphere (CA) preservation (oxygen concentration 2%-5%, carbon dioxide concentration 3%-5%) can be used for long-term storage of 3-6 months. Before warehousing, pre-cooling treatment is required to quickly reduce the fruit temperature to about 0℃ to avoid condensation and rot caused by temperature fluctuations after warehousing; the warehouse is equipped with a gentle air circulation system to ensure uniform temperature and humidity, avoiding dehydration and browning caused by local high temperature or low humidity; regular ventilation is carried out to discharge ethylene gas accumulated in the warehouse (ethylene will accelerate fruit ripening and rot) and extend the preservation period.

•  Pears (Duck Pears, Snow Pears, etc.)

The suitable storage temperature is 0℃ to 2℃, the relative humidity (RH) is 80%-85%, and during controlled atmosphere (CA) preservation, the oxygen concentration is 3%-6% and the carbon dioxide concentration is 2%-4%, which can be stored for 2-4 months. Pears are sensitive to humidity: excessive humidity is prone to mold growth, and insufficient humidity is prone to dehydration and wrinkling. The humidity in the warehouse needs to be precisely controlled; before warehousing, fruits without damage or pests and diseases should be selected to avoid rot spread caused by damaged fruits; the warehouse needs to be inspected regularly, and rotten fruits should be removed in time to prevent cross-contamination.

Stone fruits have thin peels, high water content, vigorous respiration, fast ripening speed, easy rot and browning, and poor storage resistance. The core of storage is "low temperature preservation, high humidity and moisture retention, and rapid pre-cooling" to inhibit ripening and rot.

•  Peaches and Plums (Honey Peaches, Crisp Plums, etc.)

For short-term turnover (1-7 days), the suitable temperature is 0℃ to 1℃, and the relative humidity (RH) is 90%-95%; for medium and long-term storage (1-2 months), controlled atmosphere (CA) preservation is required, with a temperature of -0.5℃ to 0.5℃, oxygen concentration of 2%-4%, and carbon dioxide concentration of 1%-3%. Before warehousing, rapid pre-cooling is required (reduce the fruit temperature to 0℃ within 2-4 hours) to reduce respiratory consumption; use fresh-keeping boxes or breathable fresh-keeping bags for packaging to avoid extrusion damage and dehydration; the temperature and humidity fluctuation in the warehouse does not exceed ±0.5℃ to prevent fruit freezing or rot; regular ventilation is carried out to discharge ethylene gas and delay ripening.

•  Cherries and Apricots

They have extremely poor storage resistance. For short-term turnover (1-3 days), the suitable temperature is -1℃ to 0℃, and the relative humidity (RH) is 90%-95%; for medium and long-term storage (1-2 weeks), ultra-low temperature preservation is required, with a temperature of -2℃ to -1℃, combined with a controlled atmosphere (CA) system (oxygen concentration 1%-3%, carbon dioxide concentration 2%-4%). Cherries and apricots have fragile peels and are prone to mechanical damage and freezing damage. They should be handled with care during warehousing and packed with shockproof fresh-keeping packaging; the warehouse is equipped with anti-frost equipment to avoid fruit damage caused by frost; regular inspections are carried out to timely handle rotten fruits and reduce losses.

Berry fruits have soft pulp, extremely high water content (85%-95%), thin peels, easy damage, rot and dehydration, and extremely vigorous respiration. They are the most difficult fruits to store. The core of storage is "ultra-low temperature preservation, high humidity and water locking, and sterile protection" to maximize the delay of rot and dehydration.

•  Strawberries and Mulberries

They have extremely poor storage resistance and are only suitable for short-term turnover (1-2 days). The suitable temperature is 0℃ to 1℃, and the relative humidity (RH) is above 95%. They need to be packed in sterile fresh-keeping boxes to avoid extrusion and pollution; rapid pre-cooling is required before warehousing to remove field heat and reduce respiratory consumption; the warehouse needs to be kept clean and disinfected regularly to avoid mold growth; mixing with other fruits with peculiar smells is prohibited to prevent odor contamination.

•  Blueberries and Grapes

For short-term turnover (3-7 days), the suitable temperature is -1℃ to 0℃, and the relative humidity (RH) is 90%-95%; for medium and long-term storage (1-3 months), controlled atmosphere (CA) + ultra-low temperature preservation is required, with a temperature of -2℃ to -1℃, oxygen concentration of 1%-2%, and carbon dioxide concentration of 3%-5%. Blueberries need to be packed in vacuum fresh-keeping packaging to prevent dehydration and oxidation; grapes need to retain their stems and be packed in breathable fresh-keeping bags to avoid fruit drop and rot; the warehouse is equipped with an efficient anti-frost system to avoid fruit damage caused by frost, and at the same time control the ethylene concentration to delay ripening and rot.

Citrus fruits have a waxy layer on the peel, strong storage resistance, moderate water content and gentle respiration, but are prone to peel wrinkling, rot and flavor fading. The core of storage is "low temperature and constant temperature, medium humidity and moisture retention, and ventilation" to inhibit mold reproduction and dehydration.

•  Oranges and Tangerines

The optimal storage temperature is 3℃ to 5℃, the relative humidity (RH) is 80%-85%, and they can be stored for 2-3 months; using controlled atmosphere (CA) preservation (oxygen concentration 5%-8%, carbon dioxide concentration 2%-3%) can extend the storage period to 4-6 months. Before warehousing, they need to be cleaned and dried to remove surface moisture and avoid mold growth; use mesh bags or fresh-keeping boxes for packaging to avoid extrusion damage to the waxy layer of the peel; regular ventilation is carried out in the warehouse to discharge ethylene gas, maintain air circulation, and prevent peel wrinkling and rot.

•  Grapefruits and Lemons

They have stronger storage resistance. The suitable temperature is 2℃ to 4℃, the relative humidity (RH) is 75%-80%, and they can be stored for 3-6 months. Grapefruits have thick peels and can be stored in bulk, but extrusion should be avoided; lemons need to be packed in breathable fresh-keeping bags to prevent dehydration and oxidation; the temperature and humidity in the warehouse need to be stable to avoid peel discoloration and rot caused by temperature fluctuations.

Tropical fruits are thermophilic and afraid of cold, sensitive to temperature, prone to freezing damage, vigorous respiration and fast ripening speed. The core of storage is "medium temperature preservation, moisture retention and ventilation, and temperature control to prevent cold damage" to avoid freezing damage and over-ripening.

•  Bananas and Mangoes

The suitable storage temperature is 12℃ to 15℃, the relative humidity (RH) is 85%-90%, and they can be directly warehoused for short-term turnover (3-7 days); for medium and long-term storage (1-2 weeks), controlled atmosphere (CA) preservation is required (oxygen concentration 5%-7%, carbon dioxide concentration 1%-2%). Bananas and mangoes are extremely sensitive to low temperatures: temperatures below 10℃ are prone to freezing damage (blackened peel, soft and rotten pulp), so the temperature in the warehouse must be strictly controlled; before warehousing, fruits with 70%-80% maturity should be selected to avoid accelerated rot of over-ripe fruits; the warehouse needs to be ventilated to discharge ethylene gas and delay ripening.

•  Durian and Dragon Fruit

The suitable temperature for durian is 15℃ to 18℃, the relative humidity (RH) is 80%-85%, and it can be stored for 1-2 weeks; the suitable temperature for dragon fruit is 10℃ to 12℃, the relative humidity (RH) is 85%-90%, and it can be stored for 2-3 weeks. Durian has a strong odor and needs to be stored in a separate partition to avoid odor contamination with other fruits; dragon fruit has a thick peel and can be stored in bulk or in fresh-keeping bags to avoid extrusion damage; the temperature in the warehouse needs to be kept stable to avoid fruit deterioration caused by fluctuations.

•  Medium Temperature Fresh-Keeping Warehouse (10℃ to 18℃)

Suitable for tropical fruits such as bananas, mangoes and durian, the suitable insulation panel thickness is 100mm. This thickness can effectively block the penetration of external heat, maintain a medium temperature environment in the warehouse, and balance energy saving and economy; if the region is hot in summer (outdoor maximum temperature ≥35℃) or has high humidity (annual average humidity ≥75%), it can be slightly adjusted to 120mm to improve the thermal insulation and moisture-proof effect, reduce the operation load of refrigeration and dehumidification equipment, and avoid condensation in the warehouse; the warehouse is equipped with a gentle air circulation system and a humidity control system to ensure uniform temperature and humidity.

•  Low Temperature Fresh-Keeping Warehouse (0℃ to 5℃)

Suitable for pome fruits and citrus fruits such as apples, pears, oranges and tangerines, the suitable insulation panel thickness is 150mm. This thickness is the conventional standard thickness for fruit cold storage, which can ensure that the temperature fluctuation in the warehouse does not exceed ±0.5℃, the humidity is stable within the specified range, effectively reduce energy consumption, balance the thermal insulation and moisture retention effect and construction cost, and is the most widely used thickness specification in the fruit industry; the joints of the panels need to be sealed and thermally broken, and the gaps are filled with sealant to reduce cold bridge loss and moisture penetration, preventing condensation in the warehouse; at the same time, air-cooled evaporators (ACE) are matched to improve the uniformity of temperature and humidity.

•  Ultra-Low Temperature Fresh-Keeping Warehouse (-2℃ to 0℃)

Suitable for berry fruits such as cherries, blueberries and grapes, the suitable insulation panel thickness is 200mm (if stored below -2℃ for a long time, it can be upgraded to 250mm). This type of cold storage needs to maintain a stable low-temperature environment. Thicker panels can effectively block the penetration of external heat, avoid cold air loss, and reduce the operation load of refrigeration units (RUs), thereby lowering operational energy consumption; the panels need to pass the -30℃ low-temperature shrinkage test with a deformation rate ≤0.5% to ensure stability in low-temperature environments; the warehouse is equipped with efficient frost-proof and defrosting equipment (such as electric defrosters), combined with an AI defrosting system, to prevent frost accumulation from affecting the preservation effect, and control the temperature fluctuation during defrosting ≤0.5℃ to avoid fruit freezing damage.

•  Selection of outer panel material

Adjust according to the use scenario. 304 stainless steel plates (thickness 0.6-1.0mm) are preferred, which have the advantages of corrosion resistance, easy cleaning and no odor, adapting to the humid and fruity environment of fruit cold storage and meeting food hygiene requirements; for coastal or high-salt fog areas, 316L stainless steel plates (thickness 0.8-1.2mm) can be selected, which have stronger corrosion resistance and salt fog resistance to avoid moisture and rust of the panels; for ordinary low-temperature fresh-keeping warehouses, color steel plates (thickness 0.4-0.6mm) can be selected, which have the advantages of rust prevention, decoration and economy. Moisture-proof and anti-corrosion treatment (such as applying anti-corrosion coating) should be done to avoid the panels being eroded by fruit water vapor.

•  Regional adjustment principle

In cold northern regions (outdoor temperature below -20℃ in winter), the thickness of insulation panels in the same temperature range can be increased by 30mm-50mm to improve the thermal insulation effect and reduce energy consumption. At the same time, cold-proof curtains are matched to reduce cold air loss when the cold storage door is opened. In hot and high-humidity southern regions (outdoor maximum temperature ≥35℃, annual average humidity ≥75%), it can be slightly increased by 20mm-30mm, and equipped with efficient dehumidification equipment to balance thermal insulation, moisture-proof and cost, and avoid panel damage and fruit rot caused by condensation in the warehouse. For large-scale fruit cold storage (storage capacity ≥1000㎡), due to the higher difficulty in temperature and humidity control, it is recommended to increase the thickness by 30mm on the basis of the corresponding thickness, and optimize the layout of refrigeration units (RUs) and humidity control systems to improve the uniformity of temperature and humidity.

•  Insulation, moisture retention and frost prevention details

The cold storage door must be equipped with airtight strips, automatic door-closing devices and observation windows, matched with the thickness of the insulation panels, and added with cold-proof insulation layers to avoid cold air loss and external moisture entry. Cold bridge parts must be thermally broken and equipped with cold bridge blockers to prevent condensation and frost in the warehouse. The ground must be equipped with a ventilation elevated layer to prevent foundation moisture, and at the same time facilitate cleaning and disinfection. The ground of the fruit cold storage must be anti-leakage treated (such as laying epoxy resin floor) to avoid erosion by fruit juice. The walls and ground in the warehouse must be smooth, flat and free of cracks, easy to clean and deodorize, and reduce mold growth. The warehouse should be equipped with frost-proof fans and defrosting systems to regularly clean frost and ensure the preservation effect. At the same time, the sealing performance of the panels should be checked regularly, and damaged parts should be repaired in a timely manner.