China has a 9000-year-long history of cereal-based alcohol production, with the use of molds (filamentous fungi) likely being one of the earliest fermentation techniques. This method later developed into the uniquely East Asian qu (koji) starter compound, containing grains, molds, yeasts, and bacteria. Recent studies have revealed that this method was already widely applied during the Neolithic period. However, much less is known about its development during the early dynastic times, and our knowledge of this innovation has mainly relied on textual materials. Here, we present direct evidence, based on microbotanical, microbial, and chemical analyses, for the fermentation method of a 2300-year-old liquid preserved in a sealed bronze bottle unearthed in a Qin tomb at Yancun, Shaanxi. The results of this research suggest that this liquid is likely a fermented beverage made from wheat/barley, rice, Job’s tears, broomcorn millet, and pulses. The fermentation starter may have been a cereal-based qu, consisting of a wide range of microorganisms, including molds (Aspergillus and Monascus), yeasts, and bacteria. Our findings suggest that the tradition of selecting suitable grains and microbial communities for brewing alcohol, possibly with a maiqu starter (primarily wheat/barley-based qu), may have been well established more than two thousand years ago.