Watermelon supply can be extended through various agricultural techniques such as early spring planting, delayed autumn harvesting, and protected cultivation. Additionally, the transportation of watermelons from north to south helps regulate availability throughout the year. In modern times, mechanical refrigeration and advanced preservation technologies have become key solutions for maintaining a steady market supply.
We utilize a small, modern cold storage facility located in a well-insulated building. It is equipped with mechanical cooling systems that allow us to control temperature, humidity, and gas composition according to the specific needs of watermelons. This environment helps extend the shelf life of watermelons significantly. For example, varieties like Harvest No. 1 and disease-resistant black giant crows can be stored for 20–60 days while maintaining high quality and market value. Below are the detailed steps involved in the process:
First, selecting the right variety. Different watermelon types have varying tissue structures and chemical compositions. Even within the same variety, environmental factors can affect these characteristics. For long-term storage, it's best to choose mid-to-late maturing, disease-resistant varieties. These should have high sugar content, good flavor, bright color, and no signs of pests or diseases on the vines or fruit surfaces.
Second, the timing and method of harvest. The maturity of watermelons depends on the variety, planting date, and accumulated heat after fruit set. To determine the right time to pick, using a non-invasive melon analyzer is recommended. The probe should be aligned with the center of the fruit. A Brix reading above 8° is ideal for cold storage. Watermelons that are too mature may be more prone to damage, leading to softness, loss of flavor, or even rotting during storage.
Harvesting should take place in the evening to help lower the fruit’s temperature. When picking, leave about 5 cm of the vine at the top to reduce water loss and prevent infection at the cut site.
Third, pre-cooling. This step involves rapidly reducing the watermelon’s temperature before placing it in cold storage to maintain its quality. One simple method is to pile the watermelons in the field and use the cool night air for pre-cooling. Then, store them before temperatures rise in the morning. During the first week of storage, cold air circulation is used to cool the watermelons through conduction and evaporation, bringing their temperature in line with the cold storage conditions. The typical storage temperature is between 8–12°C, with a relative humidity of around 80%, and the minimum temperature can be reduced to 5–6°C gradually.
Fourth, disinfection and refrigeration. Before storing, the cold storage room should be disinfected using a 0.1 mg/kg carbendazim solution for 3–6 days to ensure a clean and hygienic environment. Once the space is ready, the refrigeration system is turned on, and the temperature is initially set to 8–12°C. Over the next week, the temperature is adjusted based on the specific requirements of the watermelon variety to reach the optimal storage level.
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