Humans began exploiting cacao beans for alcohol before they started using them to make chocolate, according to new findings that push the earliest known use of cacao back about 500 years.

Residue scraped from pottery vessels dating to 1400 to 1100 B.C. indicates that residents of Honduras' remote Ulua Valley fermented the sweet pulp of the chocolate plant to make an alcoholic drink well before they began grinding the bitter seeds and mixing them with honey and chiles to produce the equivalent of modern cocoa.

The consumption of fermented cacao is much more recent than the production of wine and beer, which date to about 5400 B.C. in Iran and 7000 B.C. in China.

But the chocolate drinks, which had an alcoholic content of about 5 percent, had a special role in feasting, entertaining and binding indigenous groups together, said archaeologist John S. Henderson of Cornell University, who led the team reporting the find recently in the Proceedings of the National Academy of Sciences.

Henderson and Rosemary A. Joyce of the University of California, Berkeley, have been excavating at Puerto Escondido for more than a decade. The site has been called the "Cradle of Chocolate."

The highly valued beans were used as currency by the Olmecs and others in the region for hundreds of years.

Puerto Escondido has been occupied from about 2000 B.C. to the present. The identity of the people who lived there in the second millennium B.C. is not clear, but they might have been precursors of the Olmec, whose civilization began to emerge about 1100 B.C.

Before the current study, the oldest known use of cacao was marked by the discovery of a bottle containing traces of the material excavated from a grave in northern Belize. The bottle dated to 600 B.C.

Archaeologist Patrick E. McGovern of the University of Pennsylvania Museum heard about Henderson and Joyce's efforts and volunteered his services.

He was able to extract traces of theobromine, the characteristic marker of Central American cacao, from the surfaces of pottery shards they sent.

"The results were astounding," he said.