Olives were likely first domesticated in the Mediterranean basin some 6,000 years ago or so. It is thought that oil from the olive was one of several attributes that likely made the bitter fruit attractive enough to result in its domestication. However, the production of olive oil, that is to say, the deliberate pressing of oil out of olives, is currently documented no earlier than ~2500 BC.
Olive oil was used for variety of purposes, including lamp fuel, pharmaceutical ointment and in rituals for anointing royalty, warriors and others. The term "messiah", used in many Mediterranean-based religions, means "the anointed one", perhaps (but of course, not necessarily) referring to an olive oil-based ritual. Cooking with olive oil may not have been a purpose for the original domesticators, but it began at least as long ago as the 5th-4th century BC, as described by Plato.
Making Olive Oil
Making olive oil involved (and still does) several stages of crushing and rinsing to extract the oil. The olives were harvested by hand or by beating the fruit off the trees. The olives were then washed and crushed to remove the pits. The remaining pulp was placed into woven bags or baskets; the baskets themselves were then pressed. Hot water was poured over the pressed bags to wash out any remaining oil, and the dregs of the pulp was washed away.
The liquid from the pressed bags was drawn into a reservoir where the oil was left to settle and separate. Then the oil was drawn off, by by skimming the oil off by hand or with the use of a ladle; by opening a stoppered hole at the bottom of the reservoir tank; or by allowing the water to drain off from a channel at the top of the reservoir. In cold weather, a bit of salt was added to speed the separation process. After the oil was separated, the oil was again allowed to settle in vats made for that purpose, and then separated again.
Olive Press Machinery
Artifacts found at archaeological sites associated with making oil include milling stones, decantation basins and storage vessels such as mass-produced amphorae with olive plant residues. Historical documentation in the form of frescoes and ancient papyri have also been found at sites throughout the Mediterranean Bronze Age, and production techniques and uses of olive oil are recorded in the classical manuscripts of Pliny the Elder and Vitrivius.
Several olive press machines were devised by the Mediterranean Romans and Greeks to mechanize the pressing process, and are called variously trapetum, mola molearia, canallis et solea, torcular, prelum, and tudicula. These machines were all similar, and used levers and counterweights to increase the pressure on the baskets, to extract as much oil as possible. Traditional presses can generate about 200 liters of oil and 450 liters of amurca from one ton of olives.
Amurca: Olive Oil Byproducts
The leftover water from the milling process is called amurca in Latin and amorge in Greek, a watery, bitter-tasting, smelly, liquid residue. This liquid was collected from a central depression in the settling vats. Amurca, which had and has a bitter taste and an even worse smell, was discarded along with the dregs. Then and today, amurca is a serious pollutant, with a high mineral salt content, low pH and the presence of phenols. However, in the Roman period, it was said to have had several uses.
When spread on surfaces, amurca forms a hard finish; when boiled it can be used to grease axles, belts, shoes and hides. It is edible by animals and was used to treat malnutrition in livestock. It was prescribed to treat wounds, ulcers, dropsy, erysipelas, gout and chilblains.
According to some ancient texts amurca was used in moderate amounts as a fertilizer or pesticide, repressing insects, weeds and even voles. Amurca was also used to make plaster, particularly applied to the floors of granaries, where it hardened and kept out mud and the pest species. It was also used to seal olive jars, improve the burning of firewood and, added to laundry, could help protect clothing from moths.
The Romans are responsible for bringing about a significant increase in olive oil production beginning between 200 BC and AD 200. Olive oil production became semi-industrialized at sites such as Hendek Kale in Turkey, Byzacena in Tunisia and Tripolitania, in Libya, where 750 separate olive oil production sites have been identified.
Production estimates of oil are up to 30 million liters (8 million gallons) per year from Tripolitania, and up to 40 million li (10.5 million gal) from Byzacena. Plutarch reports that Caesar forced Tripolitania's inhabitants to pay a tribute of 1 million li (250,000 gal) in 46 BC.
Oileries are also reported from the first and second centuries AD in the Guadalquivir valley of Andalusia in Spain, where average annual yields were estimated between 20 and 100 million li (5-26 million gal). Archaeological investigations at Monte Testaccio recovered evidence suggesting that Rome imported approximately 6.5 billion liters of olive oil over the period of 260 years.
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