Important parameters for the quality of the oil
Below there are the most important characteristics of some parameters and their importance for the quality of the oil:
- acidity: the acidity limit for an extra virgin olive oil is 0.8%. Higher levels may be the result of problems occurred during the processing of the oil (too ripe olives, attacks of the olive fruit fly, etc.) and they are often combined with unpleasant sensory flaws.
- peroxides: an analysis of peroxides may reveal an oxidative alteration, that is a progressive degradation process of the oil’s fundamental compounds. If the peroxides level is high, it is a sign of advanced rancidity, with resulting unpleasant smells and flavours. A careless process of oil production may be the cause of a high level of peroxides: olives may have been harvested when too ripe, squashed and kept in unsuitable stores or the oil may have been exposed to light and high temperatures. The unit of measurement of peroxides is expressed in mEq O2/kg (milliequivalents of active oxygen per kg of oil); their value is fundamental to know the quality of the oil: for an extra virgin olive oil it mustn’t be higher than 20 mEq O2/kg. In an extra virgin olive oil, values between 5 and 10 mEq O2/kg are indicative of a good processing of healthy olives.
- ultraviolet light absorption: the analysis of this parameter is carried out by UV Spectrophotometry and it is employed to check the quality of the oil according to its exposition to light. Indeed, olive oil is very sensitive to light and this is the most important reason why it must be stored in dark glass bottles or in UV-resistant containers.
- antioxidant compounds: a specific analysis reveals the presence of phenolic compounds and tocopherols, fundamental parameters for the quality of the oil.
- Panel Test (sensory analysis): it is employed to reveal the oil’s sensory characteristics, which cannot be measured by a chemical analysis. It is an analysis carried out by 8-12 qualified specialists, selected according to the EU law. The high number of tasters is required to overcome every person’s different sensitivity to smells and flavours and to obtain a reliable average value. Tasters have to recognize pleasant (fruity, spicy, sweet, bitter…) and unpleasant (rancid, mould, metal…) sensory characteristics. Each taster, independently, assigns a mark to the perceptions they have to evaluate. The average value assigned by tasters is the Panel Test’s organoleptic evaluation. In order to be defined as extra virgin, an olive oil mustn’t show flaws at the Panel Test and receive a positive organoleptic evaluation as regards fruity flavours.
