An ancient Chinese beer recipe brewed 5,000 years ago calls for some unusual ingredients by today's standards: barley, broomcorn millets and Job's tears, as well as bits of bulbous root vegetables such as snake gourd root, yam and lily.
The Yangshao people, who inhabited northeastern China, made their beer by following a complicated fermenting process of malting and mashing together starchy plants, not unlike today's methods. They added tubers — the snake gourd, yam and lily — to sweeten the concoction.
Researchers at Stanford University were able to piece together the formula for Neolithic beer by analyzing a yellowish residue found on the remains of various clay funnels, wide-mouthed pots and jars discovered at a Yangshao site, according to a new study in the Proceedings of the National Academy of Science.
Around 2005, archaeologists unearthed the pottery from two different pits while excavating a site known as Mijiaya. When the site's contents were reported in 2012, Stanford archaeologist Li Liu suspected the items might have been used to make alcohol.
The pits were dated to between 3400 and 2900 BC, in the late Yangshao Period. The earliest written record of beer in China wouldn't appear until much later, toward the end of the Shang Dynasty between 1250 and 1046 BC.
Chinese scholars have speculated for years that the Yangshao culture brewed beer, but they lacked evidence until now, said Jiajing Wang, another Stanford archaeologist and the study's lead author. The findings suggest that the Mijiaya site was home to China's earliest brewery.
Wang and her colleagues' analysis of the 5,000-year-old beer residue revealed the tell-tale signs of an ancient "beer-making toolkit," they wrote in the study.
So the team set up their own Yangshao-style experimental brewery.
After identifying the types of grains in the pottery's residue, the researchers let various combinations of millets and barley sit in water until they began to germinate, a process called malting.
During malting, enzymes in the sprouting grains break down starches into simple sugars. That process creates distinctive pits on the grains, which the researchers noticed on both the ancient samples and their own test brew.
Once the grains had been sufficiently soaked, it was time to create the mash. The malt was drained, dried, crushed and mixed with hot water.
The mashing process caused the grains to swell, fold over and gelatinize. The researchers found similarly distorted grains in the historical samples.
The mash was then cooled to room temperature and fermented for two days in an airtight brewing container.
Further analysis confirmed the presence of calcium oxalate inside the pottery. This is the main substance in "beerstone," a byproduct of the steeping, mashing and fermentation of cereals. Beerstone settles at the bottom of brewing vessels, and archaeologists use it as an indicator of barley beer fermentation in ancient vessels.
The beerstone, together with the microscopic analysis of the grains, left little doubt in the researchers' minds that the Yangshao people were crafting their own brews.
The team members were surprised that the beer contained barley, Wang said. In China, barley would not become a staple crop for another 3,000 years.
Perhaps barley was brought to China's Central Plain not for food, as scholars previously thought, but for beer-making, the study authors wrote. Mijiaya farmers would have treated the barley as a rare, exotic food and cultivated it alongside other cereals.
"This beer recipe indicates a mix of Chinese and Western traditions — barley from the West; millet, job's tears, tubers from China," she said.