Olive oil acidity

Free acidity is an important parameter that defines the quality of olive oil and is defined as a percentage as grams of free fatty acids (expressed as oleic acid, the main fatty acid present in olive oil) in 100 grams of oil. As defined by the European Commission regulation No. 2568/91 and subsequent amendments, the highest quality olive oil (Extra-Virgin olive oil) must feature a free acidity lower than 0.8%. Virgin olive oil is characterized by acidity between 0.8% and 2%, while lampante olive oil (a low quality oil that is not edible) features a free acidity higher than 2%. The increase of free acidity in olive oil is due to free fatty acids that are released from triglycerides.

The presence of free fatty acids in olive oil is caused by a reaction (lipolysis) started when lipolytic enzymes (that are normally present in the pulp and seed cells of the olive) come in contact with the oil (that is contained in particular vacuoles) due to loss of integrity of the olive. High values of free acidity in olive oil can be due different factors such as: production from unhealthy olives (due to microorganisms and moulds contamination or attacked by flies and parasites), bruised olives, delayed harvesting and storage before processing. The lipolysis reaction is greatly enhanced by the presence of an aqueous phase, so when oil is separated from water during processing, lipolysis slows down and stops.

Free acidity is a defect of olive oil that is tasteless and odorless, thus can not be detected by sensory analysis. Since vegetable oils are not aqueous fluids, a pH-meter can not be used for this measure. Various approaches exist that can measure oil acidity with good accuracy.

...
Wikipedia