Watermelon supply can be effectively managed through various agricultural techniques, such as early spring planting, late autumn cultivation, and the use of greenhouse environments. Additionally, the transportation of watermelons from north to south helps extend their availability throughout the year. In modern times, mechanical refrigeration and advanced preservation technologies have become essential tools for maintaining a steady market supply of fresh watermelons.
To achieve this, small-scale cold storage facilities are commonly used. These are well-insulated buildings equipped with mechanical cooling systems. By carefully controlling temperature, humidity, and gas composition within the storage environment, the shelf life of watermelons can be significantly extended. For example, varieties like Harvest No. 1 and disease-resistant black giant crows can remain fresh for 20–60 days, maintaining high quality and delivering good economic returns. Below are the detailed steps involved in the process:
First, selecting the right variety is crucial. Different watermelon types have varying tissue structures and chemical compositions. Even within the same variety, environmental factors can influence these characteristics. For long-term storage, it's best to choose mid- to late-maturing, disease-resistant varieties that have high sugar content, vibrant color, and no signs of pests or diseases on the vines or fruit surfaces.
Second, proper harvesting is essential. The maturity of each watermelon depends on the variety, sowing date, and accumulated heat after fruit set. To determine the right time to harvest, a non-invasive fruit analyzer is recommended. This device measures the sugar content by aligning its probe with the center of the fruit. Watermelons with a Brix level of 8° or higher are ideal for cold storage. Harvesting at full maturity ensures better quality and reduces the risk of damage during storage, which could lead to softness, loss of flavor, or rot.
Harvesting should be done in the evening to help lower the fruit’s temperature. When picking, leave about 5 cm of the vine attached to the top of the fruit to minimize water loss and reduce the chance of infection at the cut site.
Third, pre-cooling is an important step before placing the watermelons into cold storage. This involves quickly lowering the fruit’s temperature to the desired range to preserve its quality. One simple method is to pile the watermelons in the field and let them cool naturally during the night. Before the temperature rises in the morning, they are moved into the cold storage. During the first week, cold air circulation is used to gradually cool the fruits through conduction and evaporation, ensuring even temperature distribution. The ideal storage temperature is typically between 8–12°C, with a relative humidity of around 80%. The minimum temperature can be lowered to 5–6°C depending on the variety.
Finally, disinfection and refrigeration of the storage facility are critical. Before using the cold storage, it should be sprayed with a solution of 0.1 mg/kg carbendazim for 3–6 days to eliminate bacteria and maintain cleanliness. Once the storage area is sanitized, the refrigeration system is activated, and the temperature is initially set to 8–12°C. Over the next week, the temperature is gradually adjusted to the optimal level based on the specific variety of watermelon being stored.
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