An international research team with scholars from Shandong University and Washington University in St Louis, the United States, has unearthed carbonized adzuki beans dating back 9,000 years at Xiaogao site in Zibo, East China's Shandong province.

This finding, published in the Proceedings of the National Academy of Sciences of the United States of America, predates previously known adzuki bean remains in China by 4,000 years, which rewrote the history of adzuki beans.

The Xiaogao site, located in the downstream Yellow River region, was inhabited during the Houli culture period, around 9,000 to 7,000 years ago. The researchers identified 45 adzuki beans at the site, most of which had lost their seed coats. Using carbon-14 dating, a method that measures the decay of carbon-14 isotopes to determine the age of organic materials, the team confirmed the beans' antiquity.

This discovery challenges the notion that adzuki beans originated in Japan, as previously claimed by some Japanese scholars. It also compared adzuki beans from over 140 archaeological sites across East Asia, revealing distinct evolutionary paths for beans in the Yellow River region, Japan, and South Korea.

The adzuki beans at Xiaogao site are the smallest of any archaeological finds, with an average volume of 5.8 cubic millimeters. This suggests a slow domestication process in China, contrasting with the rapid size increase seen in Japan and the Korean Peninsula's beans around 6,000 to 4,500 years ago. The findings indicate that China was likely one of the earliest regions to cultivate adzuki beans, highlighting its significant role in the crop's history.

The carbonized adzuki beans unearthed at the Xiaogao site in Zibo, Shandong. [Photo/Shandong University]

Archaeological excavations yield samples of adzuki beans and modern adzuki beans. [Photo/Shandong University]