Olive Oil through ages: Tracing 4,500 years of Mediterranean tradition

AMMAN – The Mediterranean diet has included olives and olive oil from the Bronze Age until modern times. Meanwhile, scholars from the British Museum studied traces of olives crushed at Khirbet Umm Ghozlan, located in north-western Jordan.

“A project grant from the Council for British Research in Levant enabled the project to partner with the Department of Scientific Research at the British Museum,” noted James Fraser.

“Here, Senior Research Scientist Caroline Cartwright examined all plant remains that were recovered from the British Museum excavations at Khirbet Umm Ghozlan [c.2,500 BC] near Kufr Abil in the Wadi Rayyan,” Fraser noted, adding that plant remains are organic, they decompose in the ground and so are usually not found by archaeologists. 

However, when plant remains have been burned, they become carbonised. 

"This means they preserve in the archaeological record. These are tiny remains," Fraser explained, adding that sometimes they are identified as charred fragments of wood when archaeologists are digging, and these are carefully collected for examination in the lab. 

However, really small plant remains, such as seeds and grains, are usually overlooked by archaeologists when they are digging," Fraser said, adding that these tiny remains are obtained by a process called soil flotation. 

When an archaeologist is digging a good level in their site, they collect a sample of the soil deposit for soil flotation. 

"At Ghozlan, we would take a minimum of 20 litres of dirt from every single separate level we excavated – which meant taking tens of thousands of litres of dirt in total. These dirt samples are put into a large barrel full of water, which a motor then shakes very fast while churning up the water. As the soils breaks apart, any charred seeds and grains trapped within are released, and they float to the top of the barreland collected through a sieve.

Funded by the CBRL grant, Cartwright examined all these plant remains under a scanning electron microscope in the scientific laboratories at the British Museum, Fraser continued, adding that each plant species has a different anatomical structure, just as different animals have a different skeleton. 

"By looking at each tiny fragment from three separate angles at a high level of magnification, Cartwright was able to identify all the species of wood that the people of Khirbet Ghozlan burnt as fuel, and to identify all the species of plant that they were eating," Fraser underlined, noting that the results were extraordinary. 

"We would expect typical farming villages from the period to have a wide variety of species. At the farming village of Tell Abu en-Niaj, for example, which was occupied about the same time as Khirbet Ghozlan on the Jordan Valley floor, people were burning many species of wood for fuel, including from orchards [such as fig] and wild species that grew locally [such as acacias]," Fraser said.

At Khirbet Ghozlan, the only species of wood that Cartwright identified was olive (Olea europaea). This is highly unusual, and suggests that people went to Khirbet Ghozlan in the highlands of the Wadi Rayyan to maintaining their olive trees, and that they stockpiled orchard prunings for use as fuel, Fraser said.

"Indeed, Cartwright identified the charred remains of small shoots that people would not normally collect for fuel, but which are removed when the tree is pruned," Fraser said, noting that the plant remains from typical farming villages also contain a wide range of foodstuffs, including wheat, barley, lentils, chickpeas, pomegranate, grapes and figs. 

All these species were found at Tell Abu Niaj, while rare examples of some of these grains (mostly barley) were found at Khirbet Ghozlan, about 85 per cent of the plant remains were the crushed fragments of olive stones. 

"This is the jift created by crushing the olive fruit before pressing, which is then collected and burned as fuel once the oil has been removed. These tiny fragments of broken olive seeds are the smoking gun that olive oil pressing had taken place nearby. The abundance of crushed olive stones and the rarity of other species suggests that the site was used as a specialised olive processing site during the harvest rather than as a typical village," Fraser elaborated.

Furthermore, this research is important because it demonstrates the timelessness and significance of olive oil to the cultures of Jordan. Just as olive factories today are lock-up for most of the year, so too was Khirbet Ghozlan probably empty about for ten months of the year, the scholar said. 

Fraser added that around mid-October, people came to Khirbet Ghozlan from somewhere else (probably the Jordan Valley) to harvest, crush and press the olives from their orchards nearby. 

"They collected the oil large jars, which they stored at Khirbet Ghozlan, and 24 such jars have been found in two buildings at the site. Then, once the harvest and pressing was finished, they took the jars of oil back to their home village, before returning again the following year," Fraser explained.

For many years this project is telling a story that could describe any of the hundreds of oil factories operating in Jordan today.