Quality includes the oil's acidity (from oleic acid) and such organoleptic characteristics as aroma and flavour.
Oil flavour varies with the growing location, the variety and quality of olives, and the method of harvesting. Oil colour does not influence flavour. Oil colour depends on the olive cultivar, climatic growing region, fruit maturity, physical fruit conditions at harvest and the processing and handling methods.
"Olive oil is a world commodity, like wheat or sugar, and its production and labeling are controlled by international agreement. In 1959, an International Olive Oil Agreement was developed for olive oil, and the agreement is administered by the IOOC in Madrid, Spain.
This agreement was changed in 1979 and again in 1986, with amendments added in 1990 and 1991 to include organoleptic (taste and aroma) and acidity standards for olive oil. The agreement designates "olive oil" as oil obtained solely from the olive, and it excludes any oil extracted from olives by solvents or resterification processes, and any mixtures of olive oil with other oils. The designation "pure olive oil" cannot be applied to any residue oils from olives.
There are three types of olive oil: virgin olive oil, refined olive oil, and olive oil or pure olive oil."*
Olive Oil Classifications - Organoleptic Characteristics
"The definitions below have been adopted by olive oil producing countries in the International Agreement of Olive and Table Olives of 1986.
a) Virgin Olive Oil
The oil obtained from the fruit of the olive tree (Olea Europaea) only by mechanical or other physical means under conditions, particularly thermal, that do not lead to alteration in the oil and which has not undergone treatment other than washing, decantation, centrifugation and filtration.
Extra-virgin: This type has absolutely perfect flavour and odor, and a maximum acidity, in terms of oleic acid, of 1g/100g.
Fine Virgin Olive Oil: This type has absolutely perfect flavour and odor, and a maximum acidity, in terms of oleic acid, of 2g/100g.
Semi-fine Virgin Olive Oil (or Ordinary Virgin Olive Oil): This type has good flavour and odor, and a maximum acidity, in terms of oleic acid, of 3.3g/100g, with a 10% margin tolerance.
NB: "Fine Virgin Olive Oil" and "Semi-fine Virgin Olive Oil" are commonly accepted as "Ordinary Virgin Olive Oil".
b) Refined Olive Oil
This oil, which is obtained from virgin olive oil by refining methods, which do not lead to alteration in the glyceride structure, has a maximum acidity, in terms of oleic acid, of 0.5g/100g.
c) Olive Oil
This oil, which consists of a blend of virgin olive oil (except lampante) and refined olive oil, has a maximum acidity, in terms of oleic acid, of 1.5g/100g.
d) Virgin Olive Oil Not Fit for Consumption As It Is
This designated virgin olive oil lampante, which is intended for refining or for technical purposes, has an off-flavour and/or off-smell and a maximum acidity, in terms of oleic acid, of more than 3.3%g/100g.
e) Olive Pomace Oil
This oil, which is a mixture of refined olive residue oil and virgin olive oil (except lampante), has a maximum acidity, in terms of oleic acid, of 1.5g/100g.
f) Crude Olive-pomace Oil (Crude Olive Residue Oil)
This oil, to the exclusion oils obtained be re-esterification processes and any mixture with oils of other kind, is obtained by treating olive pomace with solvents.
g) Refined Olive-pomace Oil
This oil, which is obtained from crude olive-pomace oil by refining methods not altering its initial glyceridic structure, has acidity of not more than 0.5g/100g."**
* Producing Olive Oil in California: 1994
** Olive Oil Chemistry and Technology