By looking, touching, thumping and listening, Cao Jinghua, 57, can tell how sweet and ripe a watermelon is in three seconds.

A watermelon verification expert from Likou township of Shangqiu, Henan province, Cao has become much busier lately, selecting the best quality melons in Zhongwei, Ningxia Hui autonomous region.

"As the arrival of this year's sanfu days, refreshing heat-relieving fruits, such as watermelons, have received a warm welcome," he said, noting that watermelons began to ripen in the region at the end of June.

Sanfu in the Chinese lunar calendar usually refers to the three 10-day periods that are predicted to be the hottest days of the year, called toufu or chufu (mid-July), zhongfu (late July to early August), and mofu (mid-August).

"Watermelons grown in Zhongwei have thin rinds and sweet red pulp," he said. "Also, the watermelons are relatively firm, which makes them suitable for long-distance transportation."

Cao and his assistants will stay in Zhongwei until mid-August and send selected watermelons to the provinces of Jiangxi, Fujian and Guangdong.

Cao's hometown — Likou township — has a history of more than 40 years planting watermelons. Around 800 hectares of farmland in Likou have been planted, typically yielding an output of 60 metric tons per hectare. The town's annual output value of watermelons can reach 120 million yuan ($16.5 million).

The national push for quality has given rise to demand for watermelon whisperers like Cao, who have learned to identify the best fruit.

"There are about 150 watermelon verification experts from our township who are distributed throughout the country's watermelon producing areas. They are engaged in melon inspections, purchasing, marketing and management work," said Cao Chongchao, Party secretary of the town's Gaozhai village. "I can feel the growth of the industry in recent years."

The village also promotes mutual help policies during the busy melon purchase season.

"During the summer harvest season, we will coordinate and organize residents to help the watermelon inspectors do their work on the farms," said Cao Chongchao.