Study Finds Olive Oil Residue Identification in Ancient Pottery May Be Flawed

A recent study led by Cornell University indicates that the chemical composition of Mediterranean soils could have caused archaeologists to incorrectly identify olive oil residues in ancient pottery. This finding challenges longstanding assumptions about the presence of olive oil in archaeological contexts.

For archaeologists, detecting traces of olive oil in ancient vessels has been crucial for understanding trade networks, agricultural practices, household habits, and the economic significance of olive oil in the Mediterranean region. However, the new research suggests that some of these chemical traces may not be as reliable as previously thought.

The interdisciplinary team at Cornell, which included classicists, food scientists, and engineers, discovered that plant oil residues degrade poorly in calcareous Mediterranean soils. This is significant because chemical residue analysis of pottery has often been used to identify olive oil. The study indicates that these residues might have been misinterpreted as olive oil, confused with other plant oils, or even mistaken for animal fats in some cases.

These findings were published in the Journal of Archaeological Science.

Challenges in Analyzing Ancient Residues

The research project began in 2019 with Rebecca Gerdes, then a doctoral student in Cornell’s Department of Classics. Gerdes, who also had an undergraduate background in chemistry, aimed to apply her scientific training to archaeological residue analysis.

“I usually describe my work as: I wash ancient dirty dishes, I save the rinse liquid, and I use the molecules in it to figure out how people are using their pots,” Gerdes said. She currently holds the Hirsch Postdoctoral Associate position at the Cornell Institute of Archaeology and Material Studies.

Organic residue analysis is a well-established archaeological method that examines molecular traces left in ancient containers. Yet, Gerdes observed that many claims about olive oil in eastern Mediterranean pottery were based on untested assumptions about the region’s soils.

Following advice from her Ph.D. advisor, Sturt Manning, Distinguished Professor of Classical Archaeology, Gerdes focused initially on improving the analytical methods rather than addressing historical questions directly.

“One of the things that I was realizing early in my Ph.D. was people were making all sorts of claims about what they had found in pots in the eastern Mediterranean, and there was a lot of room for backing those claims up with more solid experimentation,” she explained. “I wanted to answer some interesting archaeological questions, but I realized I had to do some method development first.”

This realization led to a broad collaboration across Cornell, involving researchers from multiple colleges and facilities.

Impact of Soil Chemistry on Residue Preservation

Jillian Goldfarb, associate professor of chemical and biomolecular engineering, played a key role in the project. Her lab’s expertise in studying organic waste decomposition for biofuel research provided tools adaptable to analyzing ancient food residues.

Due to pandemic restrictions, Gerdes could not collect soil samples directly from Cyprus. Instead, Mediterranean soil was sent to Cornell, sterilized by the Cornell Soil Health Lab, and made available for study. Bob Schindelbeck, the lab’s director, assisted Gerdes in understanding how soil chemistry influences residue survival on pottery.

Gerdes designed an experiment using small ceramic pellets made from rolled terracotta clay, which were soaked in olive oil and buried in two types of moist soil: one from a New York agricultural field and another from Cyprus, selected for its similarity to archaeological site conditions.

“What turns out to be critical is this soil is really common in the eastern Mediterranean, so it impacts a lot of major historical periods, especially where we’re looking at trade and connectivity in that region,” Gerdes noted. She identified the Late Bronze Age (circa 1650-1100 BC) as one such period affected.

To accelerate the aging process, the samples were incubated at 50 degrees Celsius for up to a year before excavation and molecular analysis.

“We managed to do it in the lab at an accelerated rate, so we didn’t have to wait 3,000 years to finish my Ph.D.,” Gerdes said.

Olive Oil Residue Degradation and Misidentification

The experiment demonstrated that the calcareous, alkaline Cyprus soil altered the residue profile. Ceramic pellets buried in this soil retained less olive oil residue and lost dicarboxylic acid biomarkers typical of plant oils compared to those buried in mildly acidic New York soil.

This degradation complicates residue interpretation because olive oil shares molecular characteristics with other plant oils. As it breaks down, its chemical signature can resemble animal fat, making it difficult to distinguish.

“There’s definitely a sense among archaeologists of wanting to believe that you found olive oil, because it makes a nice story. And because it’s such an economically important Mediterranean product, there is a default assumption that if you found molecules that match olive oil, then you must have found olive oil,” Gerdes said. “The problem is that olive oil overlaps in its composition with a bunch of other plant oils. And if you start to degrade it, then it gets even worse – it starts looking like an animal fat.”

Interdisciplinary Collaboration and Future Directions

Gerdes emphasized the importance of the collaborative approach that brought together expertise beyond classical archaeology. The project utilized laboratory space at the Boyce Thompson Institute, with assistance from Joe Regenstein, professor emeritus of food science, who aided in developing the extraction process for organic residues.

Goldfarb’s team applied chemical engineering methods from biofuel research to quantify residues, while the Cornell Center for Materials Research and the Cornell Stable Isotope Lab provided support for handling samples and cleaning equipment.

Undergraduate co-authors Hanna Wiandt, Malak Abuhashim, and Avery Williams contributed to the research, which required the development of a shared vocabulary and goals across disciplines.

Goldfarb highlighted the potential for Cornell to establish a leading interdisciplinary center for biomolecular archaeology.

“We really want to build out an analytical center for this,” she said. “We’re thinking about how engineers and scientists can be of use in building out new methodologies and applying the fundamental skills and the applied skills that we have to new knowledge areas. And it all starts with one amazing student – now a postdoc – to get the conversations going.”

The study, titled “Overlooking environmental context causes misidentification of ancient Mediterranean plant oil in organic residues,” was authored by R.F. Gerdes, H. Wiandt, M. Abuhashim, A. Williams, J.M. Regenstein, S.W. Manning, and J.L. Goldfarb. It was published on 24 November 2025 in the Journal of Archaeological Science (DOI: 10.1016/j.jas.2025.106426).

The research received funding from the National Science Foundation; Cornell’s Department of Classics, the Cornell Institute of Archaeology and Material Studies, the Engineering Learning Initiatives, the Mario Einaudi Center for International Studies, and the Institute of European Studies; as well as the American Society for Overseas Research.