Earliest evidence of wine found in giant jars

At the next dinner party, when the discussion turns to politics and you reach for a second glass of wine, consider this: your social lubricant has 8000-year-old roots. People were fermenting grapes and storing wine in massive jugs as long ago as 6000 BC, according to a study published this week in the Proceedings of the National Academy of Sciences.

The new research pushes chemical evidence of wine 600 to 1000 years before the previous oldest estimates.

‘‘This is a big time jump,’’ said Patrick McGovern, an expert in ancient wines at the University of Pennsylvania Museum and an author of the new study. McGovern and his colleagues analyzed pottery jars found in the Eurasian country of Georgia that dated to the early Neolithic period.

Ancient Georgians could have stored 300 litres of wine in the jars, which are about one metre tall. Small clay bumps are clustered around the rim. These decorations, the researchers hypothesize, represent grapes.

McGovern is confident that the pottery is old. ‘‘The radiocarbon dating is very precise,’’ he said. ‘‘We know the dating within 200 years.’’ The jars were created between 6000 and 5800 BC.

The new insights came from a break in tradition. It is common practice for archaeologists to clean ancient pottery with a gentle bath of a mild acid or base. The corrosives reveal details in the pottery often hidden beneath a crust of accumulated minerals. But these baths also erase any traces of organic compounds stuck to the pottery. In the latest excavation, the archaeologists skipped the chemical scrub. This allowed researchers to extract four organic compounds present in the potsherds: citric acid, malic acid, succinic acid and tartaric acid.

Taken together, the relatively high concentrations of these acids point to wine. ‘‘The tartaric acid establishes grapes,’’ said Andrew Waterhouse, who studies the chemistry of wine.

Grapes are the only fruit in the Georgian mountain region that produce tartaric acid, McGovern said. Some dirt-dwelling microbes can generate organic acids, but soil samples showed no signs of the chemicals at high concentrations.

Fermentation left its signature in the form of succinic acid. The combination of succinic and tartaric acid, Waterhouse said, ‘‘is completely convincing that this is grape wine.’’ A few other clues pointed to fermented grapes, too. The researchers found botanical evidence in ancient grape pollen, starch and bits of grape skin.

‘‘We can’t prove the alcohol,’’ McGovern said. That evaporated ages ago. But he doubts the Georgians were big into nonalcoholic juice. Wine flows through ancient Georgians’ culture. They drank wine to celebrate births and left wine cups and pitchers in tombs.