Li (left) and Acker add broomcorn millet to a brewing kettle at JingA. [Photo/China Daily]

After arriving in Xi'an, our group's first stop is a warehouse labeled: "Storage of Archaeological Objects No 03". Xing Fulai, the leader of the Mijaya dig, unlocks the big steel doors and pulls them apart with a loud clang. Each of us, our inner Indiana Jones primed for excitement, leans in to look.

A few minutes later, the awed modern brewers are allowed to hold some of the clay vessels used by their ancient predecessors.

"These things are more than 10 times as old as America," says photographer Aaron Berkovich.

China has a long history of alcohol production. Evidence of rice-based fermented beverage has been found at the 9,000-year-old Jiahu site in today's Hunan province, but barley-based brewing - our modern notion of beer - had not been recorded until much later.

"In China, the earliest written record of beer appears in oracle bone inscriptions from the late Shang Dynasty (c. 16th century-11th century BC)," the Stanford-Shaanxi researchers wrote in the US National Academy of Sciences journal PNAS in June 2016. "According to the inscriptions, the Shang people used malted grains, including millets and barley/wheat (barley and wheat are represented by the same Chinese character) as the main brewing ingredients." While scholars had speculated that the beer-brewing tradition dated back to the Neolithic Yangshao period, there had been no direct evidence for alcohol production from Yangshao-era sites.

The new research provided evidence of both early alcohol production and a surprise: barley.

"Barley was one of the main ingredients for beer-brewing in other parts of the world, such as ancient Egypt," Wang told National Public Radio in the US. "It is possible that when barley was introduced from Western Eurasia into the Central Plain of China, it came with the knowledge that the crop was a good ingredient for beer brewing."