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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, they tend to dehydrate, shrivel, rot, and deteriorate quickly at room temperature after harvest. To address this issue, mechanical refrigeration is an effective method for long-term storage, significantly extending the supply period. In this article, we will introduce a micro-energy-saving refrigeration technology used in two grape-growing bases in Zhangguanying and Zhuziying Townships, Lushan County, Henan Province. This technique is easy to operate, simple to manage, and can keep grapes fresh for up to six months with a good fruit rate of 98.5%.
**1. Variety Selection**
There are many varieties of table grapes, but their storage qualities vary greatly. Early-maturing varieties generally have poor storage ability, while medium and late-maturing varieties perform better. Commonly stored varieties include Longyan, Rose, Horse Milk, Kyoho, Red Earth, Black Big Grain, Autumn Black, and Ruibier.
**2. Storage Methods and Technical Points**
**2.1 Warehouse Disinfection and Cooling**
Two to three days before storing grapes, the warehouse must be thoroughly disinfected. A 1% solution of formaldehyde can be made using formalin, or the entire storage area can be treated with 40% fresh lime water. Additionally, sulfur powder (10–20 g/m³) can be used for fumigation, which should be sealed for 8–10 hours. Two days before storage, the warehouse temperature should be lowered to -2°C.
**2.2 Preparation of Fresh-Keeping Materials**
**(a) Packaging:** Grapes are packed in fresh-keeping boxes with a load of no more than 4 kg per box. Common sizes include 37×27×17 cm and 36×26×16 cm. Materials such as wooden crates, cartons, and plastic boxes are used. Polystyrene foam boxes are popular due to their good insulation properties.
**(b) Fresh-Keeping Bags:** Special PVC or PE bags are used for grapes. Since PVC bags are difficult to open, they should be purchased one month in advance. Before use, all bags must be checked for leaks and taped if necessary to prevent spoilage.
**(c) Preservatives:** Sulfur dioxide (SO₂) preparations like SM, SPM, and CT are commonly used. The dosage is typically 1–2 tablets per kilogram. For sensitive varieties, a combination of preservatives like sec-butylamine may be applied.
**2.3 Agricultural Practices Before Storage**
**(a) Fertilization:** Phosphorus and potassium fertilizers should be applied before maturity to increase sugar content and improve storage stability.
**(b) Irrigation:** Stop watering 10–15 days before harvest. If rain occurs, delay harvesting and ensure proper drainage.
**(c) Yield Control:** The yield for storage should be around 22,500 kg per hectare. Pruning and thinning help maintain uniform size and quality.
**(d) Disease Prevention:** Spray bacterial solutions, carbendazim, or serophone every 10–15 days once fruits start coloring.
**(e) Hormone Spraying:** Apply B9, Qingshui, or naphthalene acetic acid + gibberellin to prevent fruit drop and maintain stem freshness.
**2.4 Harvesting and Post-Harvest Treatment**
Harvest fully matured grapes early in the morning or in the evening when dew is present. Immediately remove damaged, small, or bruised grapes and gently place them into lined boxes. Transport to cold storage as soon as possible—ideally within 12 hours. Handle carefully during picking, packing, and transport to avoid damage.
**2.5 Rapid Pre-Cooling and Storage**
After transport, open the bags and pre-cool the grapes at -1°C to -2°C until their internal temperature drops to 0°C. Then, insert the preservative into the bag, seal it, and store at -0.5°C to 0.5°C. Maintain humidity between 85% and 95%, and oxygen levels between 2% and 5%. Ensure the preservative is placed in the center of the cluster, not touching the bag.
**2.6 Storage Management**
**(a) Temperature Control:** Keep the cold storage temperature stable at -0.5°C to 0.5°C, with a maximum difference of 1°C inside the warehouse. Stacking should allow air circulation, with gaps between stacks and walls. Use precise mercury thermometers for accurate readings.
**(b) Ventilation:** Only ventilate when the temperature difference between inside and outside is small. Avoid ventilation during rainy or foggy weather.
**(c) Timely Processing:** Remove any moldy or damaged grapes promptly.
**3. Summary of the Storage Process**
Harvest → Cut out rotten, small, or damaged grapes → Place directly into PE or PVC-lined boxes with preservatives → Pre-cool at 0–1°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