© UnknownYucatan: The peninsula is a rich source of Mayan artefacts
It's a discovery to challenge even the most ardent cocoa addict: Archaeologists have found traces of chocolate thought to be 2,500 years old. The choc of ages was discovered on a plate in the Yucatan peninsula, the first time chocolate residue has been found on a plate rather than a cup. The find suggests chocolate may have been used as a condiment or sauce with solid food, as well as for drinking.

Experts have long thought cacao beans and pods were mainly used in pre-Hispanic cultures as a beverage, made either by crushing the beans and mixing them with liquids or by fermenting the pulp that surrounds the beans in the pod. Such a drink was believed to have been reserved for the tribal elite.

But the discovery announced this week by Mexico's National Institute of Anthropology and History expands the conception of how chocolate may have been used in ancient Mexico. It would also suggest that there may be ancient roots for traditional dishes eaten in Mexico today, such as mole, the chocolate-based sauce often served with meats.

'This is the first time it has been found on a plate used for serving food,' archaeologist Tomas Gallareta said.

'It is unlikely that it was ground there (on the plate), because for that they probably used metates (grinding stones).'

The traces of chemical substances considered 'markers' for chocolate were found on fragments of plates uncovered at the Paso del Macho archaeological site in Yucatan in 2001.

These fragments were later subjected to tests with the help of experts at Millsaps College in Jackson, Mississippi, as part of a joint project.

The tests revealed a 'ratio of theobromine and caffeine compounds that provide a strong indicator of cacao usage,' according to a statement by the university.

'These are certainly interesting results,' John S. Henderson, a Cornell University professor of Anthropology and one of the foremost experts on ancient chocolate, said yesterday.

Prof Henderson, who was not involved in the Paso del Macho project, wrote that 'the presence of cacao residues on plates is even more interesting ... the important thing is that it was on flat serving vessels and so presented or served in some other way than as a beverage.'

'I think their inference that cacao was being used in a sauce is likely correct, though I can imagine other possibilities,' he added, citing options like 'the addition to a beverage (cacao-based or other) as a condiment or garnish.'

The plate fragments date from about 500 B.C., and are not the oldest chocolate traces found in Mexico.

Drinking vessels found in excavations of Gulf coast sites of the Olmec culture, to the west of the Yucatan, and other sites in Chiapas, to the south, have yielded traces around 1,000 years older.

However, the discovery embeds both the roots of Mexican cuisine and the importance of chocolate further back in time than was previously believed.