Decoding alcoholic beverage and brewing practices of the Qin state during the Warring States period (475-221 BC) based on archaeological evidence

• Multiple methods were employed to identify the ancient liquid in a Qin bronze vessel. • There were 24 classes of organic compounds detected, including nutrients and flavor compounds. • The liquid was a cereal-based alcoholic beverage made from broomcorn millet and Triticeae. • Qin people mastered brewing and qu production during the Warring States period. China is one of the earliest regions to consume alcoholic beverages in the world. More and more ancient alcoholic beverage residues have been found in China, attracting considerable attention to explore the origins of brewing and the evolution of brewing technologies. The development of interdisciplinary analytical technologies in recent years has enabled the accurate identification of alcohol residues. Recently, a large amount of liquid was found in a bronze bottle with garlic-shaped mouth, which was unearthed in a Qin tomb M39 at Shanjiabao cemetery dating to the Warring States period (475–221 BCE). The chemical analysis methods of FTIR, UPLC-Q-TOF-MS, and UPLC-QE-MS, along with the analysis of microfossil remains of starch grains, phytoliths, and yeast were applied to identify the ancient liquid. The results suggested that the liquid residue was likely a cereal-based alcoholic beverage with high concentrations of lactic acid and oxalic acid, and a low concentration of tartaric acid, as well as 23 other classes of organic compounds such as amino acids, fatty acids and carbohydrates. Microfossil results further confirmed the primary brewing ingredients were broomcorn millet and Triticeae (wheat/barley). The fermentation starter was likely qu based on the phytoliths and yeast, which was also supported by ancient texts. This study provides a clear understanding of the cereals utilisation and brewing techniques of the Qin people, contributing to the reconstruction of ancient Chinese brewing technology and also refining the development process.