By Christine McGourty BBC science correspondent

New analytical techniques were used on 2,600-year-old ceramic vessels

US scientists have discovered residues of cocoa - from which chocolate is made - in pots dating to 600 BC.

This pushes back the earliest chemical evidence of chocolate use by about 1,000 years.

The Mayans were well-known chocoholics and the latest discovery of their enthusiasm for liquid chocolate comes from jugs belonging to a collection of well-preserved spouted ceramic vessels found at the Maya archaeological site at Colha, in northern Belize, in Central America.

Small samples

It is possible that the liquid may have been poured back and forth from jug to jug to produce the froth that was considered by the Maya and the Aztecs to be the most desirable part of a chocolate drink.

Most of the ceramic vessels were found in the burial sites of elite individuals, along with bowls, dishes and plates - all known to have been manufactured only during the period 900 BC to AD 250.

Residues from 14 jugs were sent to Hershey Foods in Pennsylvania for analysis. Jeffrey Hurst of the chocolate company used a combination of high-performance liquid chromatography and mass spectrometry to analyse the tiny 0.5-gram samples and found traces of cocoa in three of the jugs.

He said they were surprised by the findings and added that the chocolate company had no interest in reviving the Mayan's chocolate recipes.

Not the same

"It was a fun project to work on," he told BBC News Online. "But the recipe is nothing like the chocolate taste we gravitate towards today.

"My guess is if you want to know what it tasted like in the time of the Mayans, take a blender and mix cocoa with water and maybe some spices. It's not really something I'd like to try."

The evidence suggests chocolate was not eaten as an occasional snack or used as a sweet ingredient in puddings as it is today. Instead, it was consumed with most meals, usually mixed with another ingredient, such as water, maize, chilli and/or honey.

The jugs would have been used to pour the liquid from the spout, in the same way we use a teapot today. Documents written at the time of the Spanish Conquest suggest liquid chocolate was agitated to produce a foam.

The discoveries in northern Belize indicate this may have been one of the main production areas for chocolate during this period.

The Mayan pot research is published in the journal Nature.