To achieve optimal results when storing kiwifruit, it's advisable to use a rapid oxygen reduction controlled atmosphere method, and to do so under appropriate low-temperature conditions. Low-temperature controlled atmosphere not only inhibits the respiration of the fruit and the production of ethylene, delaying its ripening, but also, in a sealed environment, maintains a higher relative humidity, reaching above 90%, keeping the fruit fresh and plump.

The specific operation of low-temperature controlled atmosphere storage is as follows: After the fruits are pre-cooled and graded, they are packed into fruit boxes with a capacity of 10-15 kilograms per box. Then, a plastic bag with a thickness of 0.06-0.08 millimeters is placed over the box. Ventilation holes are provided on top, covered with rubber tubes, and the bag is sealed or the ventilation holes are clamped shut to form a closed system. Each fruit box is placed on a rack inside the cold storage. The temperature in the cold storage is maintained at 0-2°C. All operations must be conducted within the cold storage. If oxygen-depleting machines and nitrogen are available, the rapid oxygen depletion method is used. First, the air inside the bag is extracted using a vacuum pump, followed by nitrogen inflation, repeated 2-3 times to reduce the oxygen level inside the bag to the desired level. In the absence of nitrogen, the natural oxygen depletion method can be used, where the fruits are sealed in the bag, attempting to expel as much air as possible. No nitrogen is added; instead, the oxygen is consumed by the fruit's respiration to increase the carbon dioxide content, thereby inhibiting ethylene production. Whether rapid or natural oxygen depletion, gas measurements must be taken daily. Oxygen levels below 2% and carbon dioxide levels above 5% require oxygen supplementation and carbon dioxide removal to prevent damage from hypoxia and high carbon dioxide levels. Carbon dioxide removal is typically done using a carbon dioxide removal machine in controlled atmosphere storage facilities, while in regular plastic bags, it is usually achieved with slaked lime. For large storage volumes, large tent controlled atmosphere storage is used. Suitable gas standards for kiwifruit storage are oxygen levels of 2%-3% and carbon dioxide levels of 3%-5%. Kiwifruit, native to southern China, is renowned as the "King of Fruits" for its rich nutrients like vitamin C. With the expansion of kiwifruit plantations and the improvement of people's living standards in recent years, kiwifruit has shed its noble aura and become a common sight on people's dining tables. However, kiwifruit is a typical respiration climacteric berry, with thin skin, juicy flesh, and a high susceptibility to rot. There's a saying, "Soft in seven days, rotten in ten, half rotten in two weeks." It is difficult to store kiwifruit long-term under normal conditions, which hinders further development of kiwifruit production.

One: Hardware equipment and standards required for low-ethylene gas-tight storage and preservation of kiwifruit

Our airtight cold storage facilities are crucial for the low-ethylene controlled atmosphere storage and preservation of kiwifruit. The airtightness of the cold storage must meet the following standard: after applying a pressure of 30mm water column, the pressure inside the storage should reach above 4.4mm water column within 30 minutes; otherwise, it will be impossible to create a low-ethylene controlled atmosphere environment. Our airtight cold storage achieves an internal pressure of 12mm water column under the same conditions. Additionally, to avoid affecting the internal environment and facilitate entry inspections, a small door capable of accommodating a person should be excavated slightly below the door.

Refrigeration system equipment should be compatible with the storage capacity.

(Air Control and Monitoring System Equipment, including CO2 (carbon dioxide) removal units, C2H4 (ethylene) removal units, N2 (nitrogen) generators and storage tanks, O2 and CO2 gas composition monitors, and ethylene analyzers.)

Key Technical Indicators for Low-Ethylene Gas Tension Storage and Preservation of Kiwifruit

Kiwifruit is a typical climacteric berry that is highly sensitive to the ripening effect of ethylene (C2H4). When storing and preserving kiwifruit, it is crucial to grasp three key points: first, weaken and maintain its vitality; second, reduce the ethylene concentration in the environment where the kiwifruit is stored; third, prevent kiwifruit from losing moisture. Therefore, the key technical indicators for low-ethylene controlled atmosphere storage and preservation of kiwifruit should be categorized into three types:

(1) Indicators for reducing and maintaining vitality:

1. Temperature Indicator: -0.5 to 0.50°C. Experimental results indicate that the optimal storage and preservation temperature for kiwifruit should be between -0.5 to 0.50°C. Above 0.50°C, the respiration of kiwifruit becomes active, shortening its shelf life. Below -0.50°C, during uneven cooling in storage facilities, kiwifruit near evaporators and air ducts may suffer frost damage.

2. Oxygen Concentration Indicator: 2-3%, which maintains the respiration of kiwifruit at a low level. When O2 > 3%, nitrogen (N2) should be injected to reduce the oxygen concentration.

3. CO2 concentration indicator: 3-5%. Its function is to suppress the respiration of kiwifruit. When CO2 is less than 3%, no special treatment is required under normal circumstances, as the CO2 concentration will automatically increase through the respiration of the kiwifruit. When CO2 exceeds 5%, it should be removed immediately; otherwise, the kiwifruit may suffer from CO2 poisoning.

We have reduced the ethylene concentration to below 0.02ppm. During the experiment, we used an automatic interval-type ethylene removal unit, achieving an excellent ethylene removal effect, keeping the concentration under 0.01ppm.

(3) Humidity (RH) Indicator: The humidity should be maintained above 90%. Kiwifruit will exhibit dehydration and wrinkling when the RH is below 90%. If the humidification equipment is insufficient, water should be sprinkled on the floor to increase its humidity.

III. Selecting the Appropriate Kiwifruit Variety

There are many varieties of kiwifruit, with significant differences in their storage durability. Our comparative experiments on the four kiwifruit varieties currently cultivated on our farm—Hayward, Qinmei, Yat, and Qin Cui—show that in terms of storage durability: Hayward > Qinmei > Yat > Qin Cui. After 6 months of storage, Hayward's flesh and core remain normal; Qinmei shows a hard core; Yat's core is harder, with some flesh turning white and a poorer flavor; Qin Cui's flesh has become softer. Based on these experimental results, Hayward and Qinmei are recommended for storage if kiwifruit is to be kept.

Four: Selectively store kiwifruit with good quality.

(1) Kiwifruit intended for storage must be free from any damage or blemishes, and the fuzzy coating should be well-preserved.

(W) Kiwifruit intended for storage should reach the harvest stage. The normal color of kiwifruit is yellowish-brown, with slight variations in depth due to different varieties. Kiwifruit at the harvest stage has a deeper color and better fruit quality, making it suitable for storage. Those not yet fully ripe have a lighter color and a bluish tinge, with poorer quality and a shorter storage life. Experiments show that harvesting the same variety of kiwifruit too early will significantly reduce the storage duration.

Five, ensure the thorough execution of inventory management.

Kiwi fruits ripen quickly at room temperature, thus, when storing, the following points should be taken into consideration:

Prior to storage, the cold storage has been cooled to the appropriate temperature, with excellent airtightness.

（2）The harvesting, transportation, sorting, cooling, and storage of kiwifruit are continuous and timely. Kiwifruit should be harvested and transported immediately. During harvesting and transportation, they should be transported in separate boxes to avoid damage and maintain ventilation. For long-distance transportation, cooling facilities should be available or opt for night transport. During sorting, they should be handled quickly and gently, with the sorting environment kept at a lower temperature. After sorting, they should be stored immediately, and the time from harvesting to storage should generally not exceed two days.

Six: Storage and Piling Principles

Kiwi storage and stacking should adhere to the following general principles: avoid the kiwis from pressing against each other, ensure good ventilation between boxes for easy access, and stack securely. These principles are primarily to protect the kiwis from being damaged by pressure, to maintain good air circulation for even cooling, inhibit mold growth, and keep O2, CO2, C2H4 concentrations and humidity balanced, to prevent collapse of the stacks and avoid injuries to personnel and unnecessary losses. During the kiwi storage process, we use plastic周转箱 as containers, with dimensions of 48cm x 32cm x 27cm, which are not only convenient but also effectively protect the kiwis from damage, achieving good results. When stacking, the size of each stack should be reasonably divided based on factors such as convenience, storage capacity, wind direction, etc. The bottom of the stack should be elevated 20cm off the ground, and attention should be paid to maintaining a distance of at least 40 cm between the stack and the surrounding walls to facilitate air circulation and protect the airtight layer of the storage. Then, stack upwards, adding a layer of wood every ten layers or so to make the boxes form a solid unit. After stacking, to maintain the humidity of the kiwis on top, and reduce the impact of dripping from the roof on individual kiwis, a layer of wet jute bags should be placed on top of the kiwis.

Section 7: Daily Operation Requirements

After kiwifruit is stored, the storage facility should be quickly sealed and adjusted according to the preservation and storage technical specifications. During operation, necessary inspections should be conducted as needed by entering the facility through the small door. However, note that there is severe oxygen deficiency inside the storage; oxygen supply equipment must be carried when entering.

Chapter 8: Kiwifruit Inventory Shipment

Kiwi fruit should be stored according to the principle of centralized dispatch, with the more concentrated the better, as successive dispatches can cause frequent changes in the storage environment. Through our commercial operation experiments, under suitable temperature and humidity conditions, with oxygen content in the storage room at 2-3%, carbon dioxide content at 3-5%, and ethylene concentration <0.02 ppm, the storage life of kiwi (Qinmei) can reach over 6 months, with a shelf life of not less than half a month, a good fruit rate of 98.03%, flesh hardness of 6.82 kg/0.5 cm², and a rotting rate of 0.77%. The storage life of Hayward kiwi is even longer. Compared to kiwi stored in a reference ordinary cold storage, the flesh hardness of kiwi stored in a controlled atmosphere storage room is 3.4 times higher, the proportion of normal fruit increases by 1.3 times, the number of lost fruits decreases by 61.9%, and the rate of diseased fruit decreases by 40%.