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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 2018
Accepted: 31
st
December 2018
DOI: http://dx.doi.org/ 10.24916/iansa.2018.2.2
Key words:
olive
pomace
archaeobotany
Utica
North Africa
Roman
Tunisia
Spain
sustainability
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.
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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
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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
Figure 1.
Coastal Tunisia and Libya with
major sites and regions mentioned in the text
(author).
Figure 2.
Area IV. The large lime kiln is
visible at the top of the photo while smaller
circular kiln 4022 is visible on the right-hand
side. A rectangular cistern with rounded
edges is located near the smaller kiln. Note
the dark ash scatter near the lime kiln (photo
courtesy of Andrew Wilson).
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Erica Rowan: Sustainable Fuel Practices in Roman North Africa and the Contemporary Mediterranean Basin
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were constructed. During the imperial period it had the status of
a
municipium
before achieving the higher rank of
colonia
under
Hadrian. By the mid-3
rd
century it had become an important
Christian centre. The city then declined during the Late Roman
period and was captured by the Vandals in AD 439 and then
the Byzantines in AD 534. Sometime between the early 5
th
and
mid-6
th
centuries the alluvial fans in the estuary fnally flled
with sediment, cutting the city of from the coast (Delilie
et al.
,
2015, p. 304). Around AD 700, Utica was destroyed during
the Arab invasion and only sparsely settled from the 9
th
–12
th
centuries (Ben Jerbania
et al.
,
2014).
Although originally a residential area, during the Roman
period the south-western portion of the city was a semi-
industrial zone hosting several pottery and lime kilns. From
2012 to 2014, this semi-industrial zone, labelled Area IV,
was excavated by the Tunisian-British Utica Project, a joint
collaboration between the Institut National de Patrimoine du
la Tunisie and the University of Oxford (Fentress
et al.
,
2012;
2013; Ben Jerbania
et al.
, 2014). The Area IV excavations
revealed a lime kiln and eight pottery kilns, dating from
the early 1
st
century BC to 2
nd
century AD (Figure 2). The
kilns were used to fre a range of coarse ware including
jugs, unguentaria and chamber pots (Ben Jerbania,
et al.
,
forthcoming).
Flotation samples were collected from all areas of interest
including the insides of the kilns, rake-out pits, ash scatters,
and foor surfaces. A minimum of 10 l was collected for each
sample whenever possible, although just over 100 l was
sometimes taken from ash scatters or rake-out pits (which are
probably the same thing). A full description of the fotation
processes, along with the complete archaeobotanical and
charcoal data sets will be published in the forthcoming
Utica volume. Here, the discussion will be restricted to a
brief discussion of the fnds of carbonized olive endocarps
(Ben Jerbania
et al.
, forthcoming).
To date, 21 samples, representing 15 contexts and 188 l,
or 1/3 of the total volume of Area IV material, have thus
far been sorted and identifed. All samples with identifable
material contained at least one carbonized olive stone
fragment (Table 1). In total, there were 9 whole olive stones
and 5997 fragments recovered. Charcoal was always present
along with the olive stones. The only sample without any
fnds, and therefore the only one without any olive was 4213,
a very small sample taken from a shallow cut. As Table 1
demonstrates, sample 4075.1 contained by far the greatest
number of olives. In six samples olives were the only fnds,
and usually in small quantities. The remaining 14 samples
vary signifcantly in their numbers of olive stone fragments,
from 2 to 4776. In samples with 10 or more fragments,
excluding sample 4075.1, absolute counts varied from 18 to
433, while density levels ranged from 2.4 to 50.9 fragments
per litre (Figure 3).
As stated above, pomace residue assemblages typically
consist of fragmented olive stones recovered in large
Table 1.
Raw olive stone counts and context descriptions.
SampleContext descriptionLitresWholeHalvesFragments
4007
Upper fll of small kiln 4022
40018
4007.1
Upper fll of small kiln 4022
1200166
4009.5Ashy dump of ceramic waste near lime kiln 40039007
4046Deposit of charcoal from lime kiln 4003 rakeout pit 800132
4058Ashy layer in NE corner of main trench110052
4072.1Bottom of small kiln 402215002
4072.2Bottom of small kiln 402211.50034
4075.1
Upper fll of small kiln 4071
124124476
4078
Lower fll of lime kiln 4003
13003
4078.3
Lower fll of lime kiln 4003
15001
4078.6
Lower fll of lime kiln 4003
12001
4078.7
Lower fll of lime kiln 4003
9001
4078.9
Lower fll of lime kiln 4003
13001
4079.2
Bottom fll of plaster lined tank
100042
4093Contents of a ceramic pot40031
4113
Ashy pottery dump in fring pit of kiln 4159
4.5002
4168
Lowest fll of a cistern
7.800215
4187.5
Large ash deposit/pottery dump
9.51022
4213Dark grey ash deposit0.4000
4216.1Possible kiln rakings from kiln 421851035
4222.2Deposit of dark grey ashy silt on top of kiln 42188.5311433
TOTAL194.29235674
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quantities from concentrated deposits. The composition
and characteristics of the entire Utica olive assemblage,
in addition to their fnd spots, leaves little doubt that olive
pressing waste, in conjunction with charcoal, was being
used to fre the kilns. Sample 4075.1, with 4776 fragments
and a density of 400 fragments per litre, was collected from
inside a small kiln and therefore represents the mixture of
olive pomace and charcoal that was used during the fnal
fring. Similarly samples 4007 and 4007.1, with 18 and
166 fragments respectively, were both recovered from
inside small kiln 4022 (Figure 4). Sample 4046, with
132 fragments, came from the rake-out pit of the large lime
kiln. Although the majority of the remaining samples contain
much lower quantities, the long period of activity in this area
of the city means that some olive stone scattering is expected
and the contexts with small quantities probably represent
dispersed fuel. Moreover, 99.8% of the Area IV olive
assemblage consisted of fragments rather than whole olives.
Although post-depositional activities such as trampling can
lead to fragmentation, we would still not expect the ratio
of fragmented to whole olives to be so imbalanced if this
was a cooking waste or ritual assemblage. Similar ratios
of fragmented to whole olive stones are present in the
carbonized assemblages recovered from bakeries in Pompeii
and the
Cardo V
sewer in Herculaneum (Monteix, 2009;
Rowan, 2015; 2017). Finally, although not discussed here
in detail, the samples contained few other archaeobotanical
remains and the olive stones dominate the assemblage. Thus
the quantity, degree of fragmentation and concentrated
nature of the deposits leaves no doubt that the Romans were
using olive pressing waste to fre these kilns. Consequently,
it is now possible to add Utica to the list of North African
sites with secure archaeobotanical evidence for the use of
this vital and renewable fuel source.
3. Pomace use in Roman North Africa
In North Africa, the huge increase in olive oil production
during the Roman period altered both the regional landscape
Figure 3.
Density ratios for samples with 10
or more carbonized olive stone fragments.
During calculations, olive stone halves were
added to the total number of fragments.
Figure 4.
Kiln 4022, which went out of
use in the 2
nd
century AD (photo courtesy of
Andrew Wilson).
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Erica Rowan: Sustainable Fuel Practices in Roman North Africa and the Contemporary Mediterranean Basin
152
and the economy. It has been noted by several scholars that
there was an increase in North African pottery production
following the “olive boom” (Mattingly, 1988a; Hitchner,
2002, p. 78; Mackensen, 2009, p. 38; Lewit, 2011,
pp. 318–322; Hobson, 2015a, pp. 117–119, 140; Hobson
2015b, p. 219). The main products were African transport
amphorae, coarse ware and African Red Slip (ARS), all
designed for export and subsequently found throughout the
Roman world (Bonifay, 2007; Stone, 2009; Hobson, 2015b,
p. 210). In Tunisia, amphorae and coarse ware tended to
be produced at sites near the coast while ARS was made
and fred primarily at inland sites (Hobson, 2015, p. 105).
Utica seems to be following this trend as the kilns were only
producing coarse ware.
Archaeobotanical evidence indicates that coastal pottery
production sites frequently used olive pomace fuel to fre
the kilns (see Figure 1). At Leptiminus, pomace was a
regular fuel source. Carbonized olive stones were found in
or near multiple kilns whose total use life ran from the 1
st
and 6
th
centuries AD (Smith, 1998; 2001; Stirling and Ben
Lazreg, 2001). Similarly at Carthage it was used for both
kilns, and domestic cooking and heating over the course
of several centuries (Ford and Miller, 1978, pp. 183–187;
Hofman, 1981, pp. 261–265; Stewart, 1984; Smith, 1998,
pp. 193–194). Finally, pomace residue was found at a late
6
th
–7
th
century AD pottery kiln at Oudhna, the only ARS
kilns to have been excavated in Tunisia (Barraud
et al.
, 1998;
pp. 114–145; Lewit, 2011, p. 319; Hobson, 2015a, p. 119).
The recovery of the olive stones at Utica situates this city
frmly within the Roman tradition of using this agricultural
by-product for pottery production.
Unfortunately, only the coastal Tunisian sites mentioned
above have been sampled for archaeobotanical material.
The inland olive oil farms and press sites have been
extensively surveyed but not excavated (for a thorough list
of surveys and associated publications, see Hobson, 2015b,
pp. 212–213). There is considerable evidence to suggest
that amphora production was linked to the inland olive oil
processing sites in the Libyan Djebel and ARS production
with inland sites in the Tunisian High Steppe (Ahmed, 2010;
Lewit, 2011, pp. 319–320; Hobson, 2015b, pp. 220–221).
Lewit (2011, p. 318–322) argues that co-location may have
taken place for the explicit purpose of using the enormous
quantities of pomace generated each year to fre the pottery
kilns. Even if they were linked, as Hobson (2015a, p. 140)
suggests, primarily for taxation purposes it seems doubtful
that such large quantities of pottery could have been made
in this dry environment without a large fuel supply. These
semi-arid inland sites contained few natural fuel sources. In
North Africa, therefore, there is a clear link between olive oil
production, pomace production and pottery manufacturing at
both coastal and inland sites.
Recent research has shown that an identical pairing of
pomace with pottery was taking place in Spain, the other
major olive oil producing region of the Roman Empire
(Romo Salas
et al.
,
2001; Bourgeon
et al.
,
2018). At the
1
st
–4
th
century AD site of Las Delicias, located on the banks
of the Genil river in the Roman province of Baetica (modern
Andalusia), excavators recovered thousands of carbonized
olive stone fragments from inside a kiln and in the area of
the nearby olive press. Here pomace was being used both
to heat the water required during pressing and to fre the
Dressel 20 amphorae required to export the oil (Bourgeon
et al.
,
2018). Consequently, this practice was not restricted
to North Africa and instead it seems to have been the Roman
practice to intentionally pair industrial-scale, olive oil
production with industrial-level, pottery production.
This highly organized and economically integrated system
had several, probably unrealized, environmental benefts.
Despite these high production levels and large fuel demands,
there is no evidence to suggest that there was widespread
deforestation in the area around Utica, or anywhere in
North Africa, during the Roman period (Kaplan
et al.
,
2009; Lewit, 2011). Signifcant deforestation seems to have
already occurred in Tunisia, particularly around Carthage,
and other areas of North Africa by 300 BC, long before
the increase in olive oil and pottery production (Hofman,
1982; Kaplan
et al.
, 2009, p. 3029). The use of pomace
decreased pressure on already limited woodland resources
and allowed for several fuel-intensive activities such as
pottery, metal, and glass production to occur simultaneously
without any environmental damage (Wilson, 2002; Rowan,
2015). In addition to these manufacturing activities and
regular domestic requirements, many of North Africa’s
larger cities, such as Carthage and Lepcis Magna, were
able to support enormous bath complexes that would have
required signifcant quantities of wood for heating (Yegül,
2010, pp. 136–144). Another advantage was that kiln frings
efectively eliminated the industrial quantities of toxic and
odorous pomace that would have quickly accumulated if left
unexploited (Ruggeri
et al.
, 2015). While ancient authors,
such as Cato (Agr. 37), suggest using some of the pomace
as a pesticide for olive trees, this limited use would not have
consumed the entire quantity of pomace produced on the
larger olive oil producing estates.
4. Roman fuel management and modern pomace use
As the use of pomace fuel continues to expand in the modern
Mediterranean, it is interesting to note that several parallels
with the Roman world are already apparent. Currently, co-
fring biomass fuels, such as pomace with coal, is the most
cost-efcient (although not the most environmentally-
friendly) way to use pomace as it does not require any changes
to the existing power-plant infrastructure (Ramachandran
et al.
,
2007, p. 2005; Intini
et al.
,
2011, p. 159). Pomace
residues, especially those associated with kilns or ovens in
the Roman world, are almost always found in association
with charcoal (Hofman, 1982; Monteix, 2009). Thus the
Romans similarly used a system of co-fring, although it was
primarily for reasons of efciency and temperature control.
One of the newer logistical, rather than technological
developments that follows the Roman practice of linking
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presses and kilns is the habit of situating power-generating
stations in areas of olive oil production. Just as ceramic
manufacturing consumes large quantities of pomace, so
too do power plants.
Plan de Acción Nacional de Energías
Renovables (2011–2020)
, and other recent government
initiatives and incentives have promoted the development
and use of sustainable fuel sources in Spain (BOJA, 2010;
PANER, 2010; García-Maraver
et al
., 2012; Maldonado,
2016; Menéndez
et al.
,
2018). Andalusia is the country’s
greatest olive oil producing region, generating 800,000 tons
of oil per year. As a result of these incentives and initiatives,
12 of the 19 electric energy-generation plants in Andalusia
use olive pressing waste as their primary fuel source
(García-Maraver
et al
., 2012, p. 479). An olive waste-to-
energy plant, outside the town of Villanueva de Algaidas in
Màlaga, processes all the olive waste, including pomace and
prunings and converts it into electrical energy (InfoPower,
2005). Due to economies of scale, the construction and
running of such waste-to-energy plants has been shown to
be fnancially proftable when placed in areas of high olive
oil production (Caputo
et al.
,
2003). Operating on a much
smaller scale, an initiative by the Provincial Deputation and
the Andalusia Energy Agency is working to replace gas-oil
boilers with biomass boilers to heat schools and other public
buildings (M.O.R.E., 2008a). While Spain leads the way in
olive pressing waste exploitation, much more can be done
to utilize this resource in both the large and smaller olive oil
producing countries of the Mediterranean (M.O.R.E., 2008a,
pp. 35–36; Vourdoubas, 2017). In Italy, 1.2 million tons of
de-oiled pomace is produced every year but very little is
used in power plants (M.O.R.E., 2008b, p. 6; Intini
et al.
,
2011). Just as the Romans had pomace utilization strategies
in place in areas with large olive oil outputs, so too should
countries today, rather than letting it go to waste (Tawarah
and Rababah, 2013, p. 146; Stamatakis, 2010).
Lebanon, for example, remains a country heavily dependent
on fossil fuels. Kinab and Khoury (2015) have suggested
taking a similar approach to the Andalusian practice of
locating energy stations in areas with high levels of olive oil
production. They propose building a treatment facility either
in northern Lebanon where olive oil production is highest or
in the centre of the country so that it is accessible to those
in both the north and the south. The treatment facility would
dry and de-oil the pomace in preparation for combustion.
They argue that the 79,000 tons of pomace generated in
Lebanon each year could cover the energy needs of roughly
8000 people if processed and burned correctly. Although
pomace has a lower calorifc value than gasoline, diesel,
propane or butane, it is nevertheless equivalent to oak,
another renewable resource. They argue that it would also
cost considerably less for the consumer than having to buy
gasoline, diesel or butane.
Olive pressing waste also remains an under-utilized
resource in Tunisia which is similarly dependent on fossil
fuels (Belloumi, 2009, p. 2752). Recent growth in the
Tunisia olive oil industry means that it is now the 4
th
largest
producer of olive oil in the Mediterranean. Approximately
175,000 tons of olive oil is produced annually, leading to
the generation of 300,000 tons of pomace and 600,000 tons
of olive waste water (Halouani, 2014; Olivea, 2017). Up to
50% of the country’s olive oil is made in the south (Olivea,
2017). Despite possessing concentrated areas of olive oil
production, no waste-to-energy plants have been constructed
and much of the olive pressing waste, and in particular the
harmful olive waste water, goes unprocessed and untreated
(Stamatakis, 2010). The installation of a biomass power
station in Thyna, Sfax, fuelled by olive pomace has been
proposed although it is unclear if construction has or will
even start (Halouani, 2014, p. 24). Olive pomace is used in
the manufacture of bricks in the Cape Bon region, but that in
no way exhausts Tunisia’s vast pomace supply (Masghouni
and Hassairi, 2000). As Tunisia continues to develop more
efcient pressing and processing methods it is hoped that
more resources will be dedicated to pairing olive oil and
pomace production with a fuel consuming activity, as once
occurred in Roman North Africa.
5. Conclusions
Olive pomace was an important and valuable resource in
antiquity from the Bronze Age through to Late Antiquity
(Mattingly, 1996; Smith, 1998; Margaritis and Jones, 2008;
Rowan, 2015; Braadbaart, Marinova and Sarpaki, 2016;
inter
alia
). Pomace was used in both domestic and commercial
settings to heat the water for olive pressings, warm homes,
bake bread and fre pottery and glass kilns. Depending upon
the taphonomy of the assemblage, pomace fuel is readily
identifable in the archaeological record, usually in the
form of a concentrated deposit of hundreds or thousands of
fragmented olive endocarps. Beginning in the 2
nd
century
AD, the Romans increased olive oil production in North
Africa by investing in the planting of new olive groves and
the construction of new presses. These olive groves extended
even into semi-arid regions with little rainfall. The increase
in olive oil enabled the growth of the pottery industry and
amphorae, coarse ware and ARS began to be made in ever
larger quantities. The coastal production of coarse ware,
and especially amphorae, is not surprising as, in addition to
olive oil, North Africa also exported large quantities of fsh
sauce and wine (Bonifay, 2004; Hobson, 2015b, p. 210). The
reasons for the inland manufacture of ARS, a product also
designed for export, is, however, more difcult to explain.
The predominant theory is that the pottery kilns were located
near the olive presses, so that the potters could take advantage
of the enormous quantities of pomace produced during the
pressing season (Lewit, 2011). Although none of the inland
kiln sites have been thoroughly excavated, archaeobotanical
evidence from several coastal sites, including Leptiminus,
Carthage and Oudhna, indicates that olive pomace was
frequently used as kiln fuel in North Africa.
The once coastal site of Utica can now also be added to
the list of North African sites that utilized pomace. Recent
excavations have uncovered a lime kiln and eight pottery kilns
image/svg+xml
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Erica Rowan: Sustainable Fuel Practices in Roman North Africa and the Contemporary Mediterranean Basin
154
situated in a semi-industrial quarter of the city. In use during
the 1
st
century BC–2
nd
century AD, these kilns similarly used a
mixture of pomace and charcoal to manufacture unguentaria,
chamber pots and jugs. Archaeobotanical samples taken from
inside and around the kilns contained hundreds to thousands
of carbonized olive stone fragments. Samples with smaller
quantities represent the spread of fuel waste rather than the
waste from ritual deposits or cooking fres. The pairing of
olive presses and kilns can also be seen at the site of Las
Delicias, located in modern day Andalusia, and undoubtedly
further archaeobotanical sampling at kiln and press sites in
Spain will continue to demonstrate this pattern.
Consequently, during the Roman period, it is possible
to observe the increasingly organized use of pomace on an
industrial scale, especially in North Africa (Ford and Miller,
1978, pp. 183–187; Hofman, 1981, pp. 261–265; Smith,
1998; 2001; Lewit, 2011; Rowan, 2015, pp. 477–478). The
Romans exploited this virtually freely-generated resource to
ensure high levels of ceramic production without, consciously
or unconsciously, causing harmful and long-lasting efects
on the landscape. There is no evidence for deforestation in
Roman North Africa, even in the already dry Tunisian High
Steppe or Libyan Djebel. Moreover, it is important to note
that they did not let this precious fuel source to go waste.
In a world with increasing fuel demands and dwindling
resources, we can learn important lessons from the highly
efcient practice of pairing presses and kilns.
Today, the Mediterranean remains the world’s major
olive oil producing region. While pomace is still used for
traditional activities, such as the fring of pottery kilns and
heating homes and pressing rooms, these practices occur
on a small scale. Much of the pomace generated each year
is not used. Over twice as much olive oil, and therefore
twice as much pomace, is generated today as was produced
during the Roman Imperial period (Mattingly, 1988a). Some
Mediterranean countries, and most notably Spain, have taken
up the Roman practice of fnding efcient ways to use up the
large volumes of pomace generated in intensive, olive-oil
producing regions. Numerous waste-to-energy power plants,
fuelled by olive pomace, have been built in Andalusia. With
an increased focus on the use of renewable and sustainable
energies, especially in the EU, the greater exploitation of
olive pomace seems to be a logical step forward.
Some countries, such as Lebanon and Tunisia, do not
yet have systems in place to exploit their olive pressing
waste, but proposals for the construction of waste-to-energy
plants have been suggested (Halouani, 2014; Kinab and
Khoury, 2015). The large body of extant and very recent
research into olive pomace fuel use is promising and it is
hoped that in the future all olive oil producing nations will
become less dependent on fossil fuels and instead turn, or
more importantly return, to the efcient exploitation of
this sustainable source of clean energy. As a renewable
fuel whose combustion has little environmental impact,
especially compared to fossil fuels, it should be included in
any discussion surrounding sustainability and environmental
impact in the Mediterranean. Thus, there is much to be learned
from the Roman pairing of agriculture and industry. As we
come to realize the value in traditional biomass resources, it
is clear that the past can provide us with important lessons on
sustainability and resource management if only we continue
to collect environmental data, study them with care, and
listen to their results.
Acknowledgements
I would like to thank Oxford’s Institute of Archaeology and
the excavation directors, Andrew Wilson, Lisa Fentress,
Imed Ben Jerbania, and Faouzi Ghozzi for inviting me to
participate in the project. I would also like to thank the
entire Area IV excavation team for their help with sample
collection. I am grateful to the Institut National du Patrimoine
in Tunisia for the excavation permits and to our project
sponsor Baron Lorne Thyssen. I would also like to thank the
reviewers for their insightful and helpful comments. Finally,
thanks go to Anna Maria Mercuri and Assunta Florenzano
for the opportunity to present these results at the 2018 CEA
conference in Modena, Italy.
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