The Ancient History of Making Olive Oil

Olive oil is, essentially, a fruit juice made from olives. 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 BCE.

Olive oil was used anciently for a variety of purposes, including lamp fuel, pharmaceutical ointment, and in rituals for anointing royalty, warriors, and other important people. 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 that began at least as long ago as the 5th–4th century BCE.

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, and 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 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 Vitruvius.

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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 50 gallons (200 liters) of oil and 120 gal (450 li) 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, and it is 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.

Industrialization

The Romans are responsible for bringing about a significant increase in olive oil production beginning between 200 BCE and 200 CE. 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.

Estimates of oil production during the Roman era are that up to 30 million liters (8 million gallons) per year was produced in Tripolitania, and up to 10.5 million gal (40 million li) in Byzacena. Plutarch reports that Caesar forced Tripolitania's inhabitants to pay a tribute of 250,000 gals (1 million li) in 46 BCE.

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 at between 5 and 26 million gal (20 and 100 million li). 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.

What Is EVOO?

There are three different grades of olive oil made and marketed, from the high-quality extra-virgin olive oil (EVOO) to medium-quality ordinary virgin olive oil, to low-quality olive-pomace oil (OPO). EVOO is obtained by direct pressing or centrifugation of the olives. Its acidity can be no greater than 1 percent; if it is processed when the temperature of the olives is below 30°C (86°F) it is called "cold-pressed." 

Olive oils with between 1 and 3 percent acidity are known as "ordinary virgin" oils, but anything greater than 3 percent is "refined," by accepted chemical solvents, and those oils can also be fairly marketed as "ordinary." 

Lower Quality Oils and Fraud

Pomace is one of the main byproducts of the pressing process; it is a conglomeration of skin, pulp, pieces of kernels, and some oil left over when the first processing is completed, but the oil undergoes rapid deterioration due to the moisture content. Refined OPO is obtained by extracting the remaining oil using chemical solvents and a refining process, then it is improved with the addition of virgin oil to obtain OPO. 

Many of the common manufacturers of olive oil practice the fraudulent mislabeling of olive oils. Since EVOO is the most expensive, it is the most often mislabeled. Mislabeling often concerns the geographic origin or oil variety of olive oil, but EVOO which has been adulterated by the addition of cheaper oils is not EVOO anymore, despite its being labeled as such. The most common adulterants in mislabeled virgin olive oils are refined olive oil, OPO, synthetic oil-glycerol products, seed oils (such as sunflower, soy, maize, and rapeseed), and nut oils (such as peanut or hazelnut). Scientists are working on methods of detection of the mislabeled olive oils, but such methods have not been made widely available. 

"Once someone tries a real extra virgin—an adult or a child, anybody with taste buds—they'll never go back to the fake kind. It's distinctive, complex, the freshest thing you've ever eaten. It makes you realize how rotten the other stuff is, literally rotten." Tom Mueller

_Sources:

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