Researchers have found the residue of a chemical compound that comes exclusively from the cacao plant - the source of chocolate - in pottery vessels dating from about 1100 BC in Puerto Escondido, Honduras.

This pushes back by at least 500 years the earliest documented use of cacao, a luxury commodity in Mesoamerica before European invaders arrived and now the basis of the modern chocolate industry.

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Cacao seeds were used to make ceremonial beverages consumed by elites of the Aztecs and other civilizations, while also being used as a form of currency.

The Spanish conquistadors who shattered the Aztec empire in the 16th century were smitten with a chocolate beverage made from cacao seeds served in the palace of the emperor. But this was not the form in which cacao had its beginnings.

"The earliest cacao beverages consumed at Puerto Escondido were likely produced by fermenting the sweet pulp surrounding the seeds," the scientists wrote in the journal Proceedings of the National Academy of Sciences.

One of the researchers, anthropologist John Henderson of Cornell University in Ithaca, New York, said cacao beverages were concocted far earlier than previously believed, and it was a beer-like drink that started the chocolate craze.

"What we're seeing in this early village is a very early stage in which serving cacao at fancy occasions is one of the strategies that upwardly mobile families are using to establish themselves, to accumulate social prestige," Henderson said.

"I think this is part of the process by which you eventually get stratified societies."

The cacao brew consumed at the village of perhaps 200 to 300 people may have evolved into the chocolate beverage known from later in Mesoamerican history not by design but as "an accidental byproduct of some brewing," Henderson said.

The chocolate enjoyed by later civilizations like the Maya and Aztecs was made from ground cacao seeds with added seasonings, producing a spicy, frothy drink.

The Spanish took cacao back to Europe in the 16th century.

Many innovations occurred in the ensuing centuries, including the advent of solid chocolate treats.

Henderson said the first use of cacao may be earlier still by perhaps a couple of centuries. Scientists now intend to test earlier pottery from the region for chemical proof.

REUTERS