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Grape Mini Energy-saving Cold Storage Technology
Grape berries are highly perishable and more than 70% of them are consumed fresh. However, fresh grapes tend to dehydrate, shrivel, rot, or change quality quickly at room temperature after harvest. To extend their shelf life and ensure a longer supply period, mechanical refrigeration is an effective solution. In this article, we will introduce the energy-saving storage technology used in two grape-growing bases in Zhangguanying and Zhuziying Townships, Lushan County, Henan Province. This method is simple to operate, easy to manage, and can keep grapes fresh for up to six months with a good fruit rate of 98.5%.
**I. Variety Selection**
There are many types of table grapes, but their storage qualities vary significantly. Early-maturing varieties usually have poor storage performance, while late-maturing ones tend to store better. Commonly stored varieties include Longyan, Rose, Horse Milk, Kyoho 2, Red Earth, Black Big Grain, Autumn Black, and Ruibier.
**II. Storage Methods and Technical Points**
1. **Disinfection and Cooling of the Warehouse**
Two to three days before storing grapes, the warehouse should be thoroughly disinfected. A 1% solution of formaldehyde can be made from formalin, or the entire storage area can be treated with 40% fresh lime water. Additionally, 10–20 g/m³ of sulfur powder can be used for fumigation, which takes about 8–10 hours. The storage temperature should be lowered to -2°C two days before the grapes are placed inside.
2. **Preparation of Fresh-Keeping Materials**
(1) **Packaging**: Grapes are packed in fresh-keeping boxes with a load of 4 kg or less per layer. Standard sizes used in production include 37 cm × 27 cm × 17 cm and 36 cm × 26 cm × 16 cm. Wooden, cardboard, and plastic boxes are commonly used, with polystyrene foam boxes being popular due to their insulation properties.
(2) **Fresh-Keeping Bags**: Special PVC or PE bags are used. PVC bags may be difficult to open, so they should be purchased one month in advance. Before use, check for leaks and seal any with clear tape to prevent fruit spoilage.
(3) **Preservatives**: Sulfur dioxide (SO₂) preparations like SM, SPM, or CT are commonly used, with 1–2 tablets per kilogram. For sensitive varieties, a combination of preservatives such as sec-butylamine is recommended.
3. **Agricultural Measures Before Storage**
(1) **Fertilization**: Apply phosphorus and potassium fertilizers before maturity to increase sugar content and improve storage stability.
(2) **Irrigation**: Stop watering 10–15 days before harvest. If it rains, delay harvesting and ensure proper drainage.
(3) **Yield Control**: Limit grape output to around 22,500 kg/ha by pruning and thinning. This ensures uniform size, high quality, and better resistance to storage.
(4) **Disease Prevention**: Spray solutions like bacillus-producing agents, carbendazim, or serophone every 10–15 days once the fruits begin to color.
(5) **Hormone Spraying**: Apply B9 (2000–4000 mg/kg) 15–45 days before harvest, or Qingshui (60–100 mg/kg) 15 days before. Naphthalene acetic acid + gibberellin can also be sprayed three days before harvesting.
4. **Harvesting and Post-Harvest Treatment**
Grapes for storage should be fully matured and harvested in the morning or evening when dew is present. Immediately after picking, remove diseased, small, or damaged fruits and gently place them into lined boxes. Transport to cold storage as quickly as possible—ideally within 12 hours. Handle carefully during packing, transport, and storage to avoid damage from bumps, pressure, or vibration. Avoid touching the fruit directly with your hands.
5. **Rapid Pre-Cooling and Storage**
Once in cold storage, open the bags and pre-cool the grapes at -1°C to -2°C until the internal temperature reaches 0°C. Then add the preservative and close the bag tightly. Maintain humidity between 85% and 95%, and oxygen concentration between 2% and 5%. Store at -0.5°C to 0.5°C for long-term preservation. Ensure the preservative is placed in the center of the bunch, not on the bottom or sides, and avoid direct contact with the plastic bag.
6. **Storage Management**
(1) **Temperature Control**: Keep the cold storage temperature stable at -0.5°C to 0.5°C, with no more than a 1°C difference across the room. Stack the grapes properly to allow air circulation and maintain spacing between stacks. Use mercury thermometers with precision of 1/5 to 1/10 for accurate temperature monitoring.
(2) **Ventilation**: Ventilate only when the indoor and outdoor temperatures are similar. Avoid ventilation during rain or fog.
(3) **Quality Monitoring**: Inspect regularly and process or sell any grapes showing signs of mold or decay promptly.
**III. Summary of the Storage Process**
Harvest → Remove damaged grapes → Place in PE/PVC-lined boxes with preservatives → Pre-cool at 0°C to -1°C for 12–24 hours → Seal and store at -0.5°C to 0.5°C.
Author: Lushan County Agricultural Radio and TV School, Henan Province