Olive oil is one of the most famous and economically-important Mediterranean products, yet tracing its ancient history is challenging: because it is a liquid, visible olive oil deposits rarely survive in archaeological settings. Archaeological organic residue analysis provides insights into the uses of ancient pottery by recovering and identifying molecular residues of organic products preserved in pottery. While some molecular biomarkers persist despite long-term environmental exposure in soils and sediments, plant oils like olive oil are challenging to identify due to the oxidation and loss of potentially diagnostic unsaturated fatty acids. Modern replica experiments use accelerated thermal degradation techniques (including cooking) and sometimes burial of pottery in an outdoor environment to approximate lipid degradation and identify biomarkers. However, thermal degradation (oxidation) at cooking temperatures does not approximate lipid breakdown related to olive oil storage. Furthermore, most environmental exposure experiments have occurred in soils from temperate climates in northwestern Europe or North America. Soil chemistry in the semi-arid Mediterranean differs significantly from these regions; however, access to climatologically-appropriate environmental exposure sites can be limited. Controlled degradation experiments on biomass for the production of renewable fuels inspired a new in-laboratory experimental design to monitor the impacts of soil chemistry and incubation temperature on the degradation of olive oil in pottery. Modern ceramic pellets were incubated over the course of a year at 25 and 50°C in initially sterile soils from a temperate climate (New York State) and a Mediterranean climate (Cyprus). Previous experimentation and preliminary results from three months of incubation suggested that temperature, the presence of ceramic, and the presence of soil affected lipid yield and rate of oxidation. These results suggest that the in-laboratory experimental design was a viable and more geographically-flexible alternative to thermally-induced degradation or environmental exposure for modeling lipid breakdown in ancient pottery.

Investigating the early history of olive oil using environmentally relevant replica experiments inspired by biofuels research

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