They may be ancient "beer-making tools", and the earliest direct evidence of beer brewing in China, the researchers reported in the Proceedings of the National Academy of Sciences.

Asia has overtaken Europe as the world's biggest beer producer for the first time in 35 years, according to a study by the research arm of the Japanese brewing giant Kirin Holdings.

"The big take-home message here isthat, as beer ages, a whole series of breakdown products grow with time, "said Tom Shellhammer, a brewing scientist at Oregon State University inCorvallis.