When an archeological dig unearths ancient pottery, for example, she works with a team of scientists to determine whether they were used to contain wine, vinegar or other fruit juices. “It’s a tricky question,” says Drieu.
Like others who study drinks in antiquity, her work is challenging and constantly evolving. Thanks to biological, archeological and chemical detective work, new scientific technologies and methods that span ancient pottery and DNA analyses are revealing the histories of alcoholic beverages worldwide.
The Chemical Fingerprint of Wine
This year, Drieu led a study that concluded that wine was traded in Sicily while under Islamic control between the 5th and 11th centuries. She and her colleagues analyzed more than 100 amphorae. Drieu developed a new method for what’s known as organic residue analysis to confirm the chemical fingerprint of wine on the ancient pottery.
“The main compound we were looking for before in wine is tartaric acid,” says Drieu. The small crystals might be familiar to wine lovers because they “grow sometimes when the wine is old,” she says.
Though tartaric acid was detected, she couldn’t confirm that wine had been in the jugs. The compound also occurs in fruits like grapes, citrus and bananas.
“This molecule is not specific to wine, and not specific to grapes,” she says.
So, Drieu also looked for the chemical signature of malic acid, another compound found in sour fruits, along with tartaric acid. She analyzed different types of fruits and liquids, like unripe grapes, tamarind, wine, grape juice and vinegar. She determined that the ratio of these two acids differed in grape products compared with most other fruits.
This method of analyzing the amounts of malic acid and tartaric acid is a more rigorous way to find out which containers once held wine, says Drieu. “At the moment, there is no way to know from chemical analysis how to differentiate between grape juice, grape syrup, vinegar or wine.”
Drieu combined her chemical research with historical written records from the medieval period to complete her study.
Ancient beer is more difficult to chemically detect than wine, Drieu says, because beer’s ingredients are used in other processes. Traces of cereal grains could be from beer production or many types of food.
To identify the remains of beer, Drieu might collaborate with an archeobotanist, or researcher who studies archeology and botany, like Tania Valamoti.
An archeobotanist at Aristotle University of Thessaloniki, Greece, Valamoti scours sites for small objects that some archaeologists might overlook, like remains of grapes and sprouted grains.
“The chemistry of natural products is a huge, huge field.” —Léa Drieu
The secret ingredient to the success of her research is fire.
“Material, at least where I work, is preserved by charring,” says Valamoti. When structures burned down thousands of years ago, the char left on the organic remains can help them persist through millennia.
Valamoti found evidence that beer has been around for thousands of years.
“I think they were probably making beer in the end of the third millennium B.C. in mainland Greece,” she says.
Valamoti came to that conclusion after she collected remains of sprouted grain, part of the malting process, from Bronze Age sites in Greece called Archondiko and Argissa that date to 2100 B.C. Dozens of small cups were also found at the sites, which may indicate they were drinking vessels for this form of Bronze Age beer.
The DNA of European Vineyards
Sites in Greece where Valamoti finds thousands of preserved pips, or grape seeds, means people were picking and eating grapes, she says. But it’s not slam-dunk evidence of winemaking.
“Whereas when we find a pure concentration of grape pips, together with grape pressings, which is the pip surrounded by the skin… [then we know] the fruit has been squashed to squeeze and extract the juice,” she says.
Then, she can conclude that people either drank the grape juice or let it ferment into wine or vinegar.
These seeds can also be ripe for DNA analysis. Nathan Wales, a lecturer at the University of York, has been able to extract ancient DNA from 900-year-old grape seeds.
In a 2019 scientific study, he examined more than two dozen grape seeds from archaeological sites in France and found an exact match to modern Savagnin grapes. This means a branch clipping may have propagated the exact same grape variety over 900 years, he says.
The ancient DNA of seeds can distinguish between winemaking grapes and table grapes, Wales says, because “there’s a pretty big [genetic] distance between those two groups.”
Drieu believes the future is bright for scientists who seek new and better ways to examine wine and beer in archaeological records.
“The chemistry of natural products is a huge, huge field,” she says, “And there’s probably a lot more work to do to find molecules that are specific to one product and that are stable enough to be preserved over centuries or millennia.”