image/svg+xml147 IX/2/2018 INTERDISCIPLINARIA ARCHAEOLOGICA NATURAL SCIENCES IN ARCHAEOLOGY homepage: http://www.iansa.eu Sustainable Fuel Practices in Roman North Africa and the Contemporary Mediterranean Basin Erica Rowan a* a Royal Holloway, University of London, Egham Hill, Egham, Surrey, TW20 0EX , United Kingdom 1. Introduction Beginning in the early Bronze Age, olive oil has been an important source of calories, fats and vitamins for those living in the Mediterranean basin (Thurmond, 2006, pp. 74–76; Salavert, 2008; Rowan, 2015, pp. 468–471; 2018). In antiquity, olive oil also served a multitude of non-dietary functions; as a fuel, a body cleanser, and a base for perfumes and cosmetics (Mattingly, 1996, p. 224). However, oil is not the only product generated by the pressing of olives. The production of olive oil results in the production of olive pressing waste, or pomace; the paste left in the baskets after the pressing is completed. This paste is made of a mixture of olive skin, fesh and broken stones. For every ton of olives pressed, roughly 200 l of olive oil and 350–400 kg of pomace are produced (Mekki et al. , 2006, p. 1419; Niaounakis, 2011, p. 414). When a traditional olive press is used the resulting pomace contains between 3.5–12% oil and 20–30% water (Karapmar and Worgen, 1983, p. 185; Azbar et al. , 2004, p. 215). Traditionally pomace is air dried, although today mechanical driers are sometimes used to speed up the process (Arjona, García and Ollero, 1999; Doymaz et al. , 2004; Göğüş and Maskan, 2006; Warnock, 2007, p. 51 Vega-Gálvez et al. , 2010). The high oil content means that once dry, pomace becomes a viable biofuel that can be used for both industrial and domestic purposes. This article will discuss the extensive use of pomace fuel in Roman North Africa before focusing on the ways in which the Romans linked olive oil and pottery production. The paper will then highlight the current state of pomace use in the Mediterranean and the valuable lessons that can be learned from ancient fuel practices.In antiquity, pomace fuel was used for a range of activities, most notably to aid in the olive pressing process, to fre pottery, lime, and glass kilns, to heat bakery ovens and for domestic heating and cooking (Margaritis and Jones, 2008; Monteix, 2009; Rowan, 2015; Barfod et al. , 2018).The burning of pomace in antiquity, especially on a large scale, means it is possible to identify and trace its use in the archaeological record. It is also possible to distinguish Volume IX ● Issue 2/2018 ● Pages 147 –156 *Corresponding author. E-mail: Erica.rowan@rhul.ac.uk ARTICLE INFO Article history Received: 7 th September 2018Accepted: 31 st December 2018 DOI: http://dx.doi.org/ 10.24916/iansa.2018.2.2 Key words: olivepomacearchaeobotanyUticaNorth AfricaRomanTunisiaSpainsustainability ABSTRACT As a readily available and renewable resource, olive pomace has been used as a fuel throughout the Mediterranean for centuries. This article will frst discuss the extensive use of pomace fuel in Roman North Africa, introducing and adding the once coastal city of Utica to our growing list of sites with archaeobotanical evidence for pomace residue. The paper will then focus on the ways in which the Romans linked olive oil and pottery production. While environmental sustainability was unlikely to have been one of the Romans’ conscious objectives, the use of this fuel was vital to the continued production of North African ceramics, particularly in more arid areas. Today, in the face of increasing energy demands, pomace is once again being recognized as an important and sustainable resource. More work, however, still needs to be done to improve the efciency of pomace use. The article will conclude by highlighting the valuable lessons that can be learned from ancient practices, especially the efcient pairing of olive cultivation and pottery production.
image/svg+xmlIANSA 2018 ● IX/2 ● 147–156 Erica Rowan: Sustainable Fuel Practices in Roman North Africa and the Contemporary Mediterranean Basin 148 pomace fuel assemblages from olives burnt for ritual purposes or as table waste. In all cases, the burning, or carbonization process, turns the olive fesh and skin to ash and as a result we are often only left with burnt olives stones (endocarps) and occasionally the seeds. Usually a pomace assemblage will appear as hundreds or thousands of fragmented olive stones in a concentrated deposit (see, for example, Smith, 1998; Margaritis and Jones, 2008; Rowan, 2015). The high degree of fragmentation is the result of crushing the olives prior to the pressing stage. Many of the olive stones will not survive combustion, especially when the pomace is subject to high temperatures such as those found inside a kiln. Consequently, a high concentration suggests large- scale and/or repeat burning events and thus pomace fuel (Mason, 2007, p. 333; Warnock, 2007, p. 47). In the case of ritual or table waste, the assemblage is usually smaller and contains a greater quantity of intact stones despite lower burning temperatures increasing the chances of preservation. Refectance measurements can also be used to confrm the use of olive pomace as a fuel and distinguish between the use of air-dried pomace and pomace that has been converted into charcoal (Braadbaart, Marinova and Sarpaki, 2016). 1.1 Current uses of pomace Today, 97% of the world’s olive oil is still made in the Mediterranean and in particular in Spain, Greece, Italy, Turkey, Morocco, and Tunisia (Christoforou and Fokaides, 2016; IOOC EU Olive Oil Figures 2018). Since 1990, EU production of olive oil has increased from 994,000 tonnes to 2.17 million tonnes or 2.36 million litres per annum (IOOC World Olive Oil Figures, 2018). 1 As olive oil output increases so too does the volume of pomace. Although the modern two- and three-phase press extraction processes make pomace output more difcult to calculate, generating 2.36 million litres of oil results in the creation of approximately 4.13–4.72 million kg of pomace. Modern press methods difer from traditional methods in that they create a more mixed and chemically toxic pulp, especially the two-phase method where all the pomace and olive waste water are mixed together. Consequently, diferent treatment methods must be applied to the pomace prior to its utilization as a fuel (for a good overview of the diferent outcomes using traditional and modern presses, see Caputo et al. , 2003 or Azbar et al. , 2004). However, since the ratio of modern continuous presses to traditional presses varies by country, for simplicity, in this article, all pressing waste with a solid component will be called pomace regardless of water content. It is beyond the scope of this article to discuss the various uses and challenges associated with olive waste water, which does not contain the fesh or stones (Niaounakis, 2011). In the light of higher energy demands and a decreasing fossil fuel supply, in addition to the challenges associated with global warming, renewable and sustainable biomass fuels such as pomace are becoming ever more important. Unlike the combustion of fossil fuels, burning pomace 1 1 litre of olive oil weighs circa 0.92 kg (Marzano, 2013, p. 99). will not increase levels of atmospheric carbon dioxide and therefore not contribute to rising levels of greenhouse gasses. Any CO 2 generated during combustion is ofset by the continued presence of olive trees and other plant matter that photosynthesizes CO 2 (Ali Rajaeifar et al. , 2016, p. 87). Experiments have shown olive pomace to be a viable alternative to fossil fuels and unlike other biomass sources such as wheat or corn, the use of pomace does not act as competition for the food supply (Intini et al. , 2011, p. 165). Throughout the Mediterranean and the Middle East pomace is still used in traditional ways. In Jordan and Syria, olive pomace is used to heat homes and cook food, while in Turkey it is used in bakeries and olive mills (Doymaz et al. , 2004, p. 214; Azbar et al. , 2004, p. 238; Warnock, 2007, p. 47–57; Rowan, 2015, p. 466). Other small-scale uses of pomace in Spain, Italy, Greece, Croatia and Slovenia include the heating of factories, private homes, and hotels, all of which make use of local resources (M.O.R.E., 2008). While these traditional small-scale uses of pomace remain important, a greater number of factories and hotels, for example, could take advantage of this resource. Unless local demand increases, pomace will continue to be generated in quantities that far outstrip local consumption. Governments, universities and research institutions have begun to dedicate considerable resources to developing more efcient ways to exploit this clean energy resource (Demicheli and Bontoux, 1996, p. 49–53; Arvanitoyannis, 2007; Vera et al. , 2014; Christoforou and Fokaides, 2016; European Commission, 2017; M.O.R.E, 2018). Some of the major olive oil producing countries in the Mediterranean have started to make use of olive pomace fuel for various industrial activities and most commonly the generation of electric and thermal energy (Demicheli and Bontoux, 1996; García-Maraver et al. , 2012). While today’s motivations are both fnancial and environmental, the drive to link industrial-scale, olive oil production with industrial-scale, energy generation is remarkably similar to the events that took place during the Roman period. 1.2 Olive oil production in Roman North Africa Roman conquest of the Mediterranean began in earnest in the 3 rd century BC. By the late frst century BC, Rome controlled all the land around the Mediterranean Sea and, in efect, all olive oil producing regions. Although olive oil was made in many parts of the Mediterranean prior to Roman hegemony, Roman territorial expansion brought about a signifcant expansion of olive groves, resulting in an increase in olive oil and pomace production (Mattingly, 1988a; 1988b). This expansion is no more readily apparent than in North Africa, which underwent an “olive boom” starting roughly in the 2 nd century AD, and reaching its peak in the 3 rd to 5 th centuries AD (Mattingly, 1988a, p. 56; 1996, pp. 235–237; Hobson, 2015a, p. 148; 2015b, p. 219). The Romans invested signifcant capital in the planting of olive groves and the construction of presses along the Tunisian and Libyan coasts, as well as in the Tunisian Sahel (Figure 1). An even more dedicated investment can be seen in the planting
image/svg+xmlIANSA 2018 ● IX/2 ● 147–156 Erica Rowan: Sustainable Fuel Practices in Roman North Africa and the Contemporary Mediterranean Basin 149 of enormous olive groves and the construction of hundreds of multi-presses sites in the Tunisian High Steppe and Libyan Djebel, semi-arid regions that only receive 200–300 mm of rainfall per annum (Mattingly, 1988a, pp. 44–45; 1996, pp. 236–237; Hobson, 2015a, p. 99). The successful planting and cultivation of these olive trees resulted in the output of millions of litres of oil. The territory around the three cities of Lepcis Magna, Sabratha and Oea in modern Libya, for example, may have been producing up to 30 million litres of oil per year (Mattingly, 1988a, p. 37). If olive oil was being produced on an industrial scale, so too was pomace (Mattingly, 1988a; 1988b; Hitchner, 2002). 2. Pomace use at Utica The site of Utica is located on the western side of the Mejerda estuary in northern Tunisia, 10 km from the coast (Hay et al. , 2010, p. 325). Originally a Punic settlement, the earliest structures date to the 8 th century BC. After the Roman defeat of Carthage in 146 BC, Utica was made the capital of the newly founded province of Africa. Although the city lost its capital status to Carthage after the Roman civil wars of the 1 st century BC, it nevertheless continued to prosper as an important port centre and many public buildings associated with large Roman cities, such as baths, basilicas and theatres