Ceramic cookware recovered at archaeological sites often contains the charred remains of food and similarly ancient residues. Researchers have long puzzled over how to interpret such finds; now, a new study published in the journal Scientific Reports is poised to provide some guidance.
Every week for a year, a team of archaeologists prepared food in unglazed clay pots and conducted chemical analyses of the materials left behind. As Nina Pullano reports for Inverse, the group tested three kinds of leftovers: charred food, carbonized patinas (or surface residues), and oils and fats that had seeped into the unglazed clay. Each one provided insights on a different point in the culinary timeline.
The burnt bits stuck to the surface of the pots contained chemical traces of the meals last cooked in the clay vessels. But while this kind of evidence might reveal the last dish made in a pot, it can’t tell archaeologists whether the recipe was a common part of a given civilization’s cuisine.
Patinas—thin layers of chemical leftovers on the surface of the pot—delve a bit deeper into the history of the cookware. They represents a mix of past cooking events, albeit skewed toward more recent meals.
Of the three types of remnants, fats and oils that seep into a pot’s unglazed clay over its lifetime are most representative of the vessel’s early history. This lipid residue “accumulate[s] and [is] replaced slowly over time,” according to Inverse, reflecting prior meals but not the most recent. (In February, an analysis of oils in ancient pottery found in Siberia showed that one community ate land animals, while another preferred fish.)
The experiment’s ingredients, tools and cleaning techniques strove to imitate ancient cooking practices as closely as possible.
“We spent a long time thinking about how we could be as true to the past as we could,” co-author Jillian Swift, an archaeologist at the Bishop Museum in Honolulu, says to the Times.
Per the study, the team prepared meals made out of whole grains like wheat and maize in La Chamba ceramic pots— unglazed, black clay cookware made in central Colombia. Co-author Christine Hastorf, an anthropologist at the University of California, Berkeley, actually set up a mill in her garage to grind the grains, according to a statement.
An arguably less savory ingredient—donated roadkill deer—also made its way into the dishes. But as Miller tells the Times, the researchers didn’t actually eat any of the meals cooked for the study.
“We chose the food based on how easy it would be to distinguish the chemicals in the food from one another and how the pots would react to the isotopic and chemical values of the food,” says Hastorf in the statement.
After each use, the chefs cleaned their pots with water and scrubbed them with branches from an apple tree. Because the vessels were unglazed (and because the team didn’t use any soap), traces of various meals stuck around.
Each of the seven researcher-cooks made the same dish every week for 50 weeks. They charred every seventh meal to replicate the samples found at archaeological sites, then gathered the blackened chunks for analysis. After the 50 weeks were up, each chef cooked a different recipe in their pot for one to four weeks, offering the opportunity to gauge whether the patinas and fatty residues reflected recent or earlier meals.
“Our data can help us better reconstruct the meals and specific ingredients that people consumed in the past,” says Miller in the statement, “which, in turn, can shed light on social, political and environmental relationships within ancient communities.”