The peroxide value, measured in milliequivalents of active oxygen per kilogram, determines the initial oxidation of an oil in a quality analysis. In other words, peroxides are chemical substances that are formed from chemical reaction of olive oil with oxygen.
Olive oil becomes oxidized when it encounters air, resulting in the formation of peroxide. This is due to the fact that the unsaturated fatty acids (monounsaturated and polyunsaturated) have one or more double links, that take oxygen and give rise to the formation of peroxides, one of the main products of oxidation
A low peroxide level means that the extra virgin olive oil is high quality. It is achieved by the extraction process during milling and the storage conditions of the oil immediately after the crush to packaging. Prior to packaging, it is important that olive oil gets stored in stainless steel tanks that are nitrogen flushed and temperature controlled, protecting the oil from light, heat, and oxygen.
The maximum peroxide value for extra virgin olive oil is 20. High peroxide levels indicate that oil has been damaged by free radicals and will give rise to aldehydes and ketones that can cause oil to smell musty and rancid. These reactions are accelerated by heat, light, and air.
High quality extra virgin olive oil should have a peroxide value below 12.
In conclusion, a very low peroxide value, the very best of extra virgin olive oil.