As China's watermelon season draws to a close this year, farmers, consumers and professional testers are of the view that during this scorching summer, selection of the juicy fruit was determined less by weight and volume, and more by taste and quality.

At a cooperative in Panggezhuang in Beijing's Daxing district, 27-year-old Zhang Linghui spent her days tapping, pressing and listening to thousands of melons at the peak of the harvest.

Zhang is one of a growing number of professional "watermelon testers" — specialists hired to judge the fruit's ripeness, sugar levels and texture. With a quick knock, she can tell whether a watermelon is unripe, overripe or just right — and only the best make it to market.

"Each watermelon has a different sound," Zhang said. "Unripe ones are hard, and the bounce hurts your fingers. Overripe melons sound dull and often crack inside. The best are nearly 80 percent ripe," she said.

A skilled watermelon tester must not only have extensive knowledge of cultivation, including the fruit's growth cycle and varietal traits, but also draw on years of experience to accurately judge its quality, she added.

Shang Ling, a 42-year-old Beijing resident, said picking a watermelon felt like opening a blind box. Although she would also tap the fruit to judge its quality before buying it at the supermarket, the result disappointed as often as it delighted.

"But now, with professionals testing them, one is more likely to find a good one," she said.

The emergence of the new trend indicates how consumer expectations are changing in one of the world's biggest watermelon markets. Once considered the luck of the draw, buying a watermelon is increasingly about quantifiable measures such as sweetness, texture and juiciness.

China plants more than 1.33 million hectares of watermelon each year and harvests around 60 million metric tons, about 60 percent of the world's total, according to the United Nations Food and Agriculture Organization. On average, each Chinese consumer eats about 50 kilograms of the fruit annually.

This summer, consumers favored thin-skinned, juicy and naturally ripened melons, according to a July report from the consumption and industry development research institute of JD, a Chinese e-commerce giant. Shoppers in their late 20s to mid-40s drove nearly 70 percent of sales, with younger buyers showing a strong appetite for new varieties, it said.

Beijing's Daxing district, Zhongwei city in the Ningxia Hui autonomous region, the Guangxi Zhuang autonomous region, Dongtai city in Jiangsu province and Shanghai are among the top sources of sales growth, according to the report.

Panggezhuang is the home of the famed Daxing watermelon, a certified geographical indication product known for its crisp sweetness. At the 2,667-hectare planting base, growers are shifting to smaller melons weighing 1 to 1.5 kg. The planting area for traditional large watermelons has already fallen to less than 66.7 hectares.

Meanwhile, farmers are also planting colorful new varieties with orange and yellow flesh or black rind to meet diverse market demands.

Song Shaotang, a local grower, is experimenting with new varieties to keep up with changing tastes. One standout is the Jingmei 3K, bred by the Beijing Academy of Agriculture and Forestry Sciences. The variety has oval-shaped fruit, deep red flesh and high sugar content, making it a hit with both farmers and consumers.

"At our demonstration field, Jingmei 3K yields stayed at about 60 (metric) tons per hectare. Customers like its color and taste," Song said, adding that his cooperative is promoting the variety in larger fields.

Xu Yong, who led the research team of the Jingmei series, said the new varieties are designed to cut breeding costs, resist disease and meet consumer preferences.

"The change from big to small melons shows how production, branding and consumption are all adapting," Xu said.

From bulk harvests of giant fruits to bite-sized melons selected by professional testers, China's watermelon industry is increasingly catering to the precise demands of summer shoppers in search of sweetness.

zhaoyimeng@chinadaily.com.cn