Peroxides, Waxes, Ultraviolet Absorption & Blending
As mentioned in Olive Oil Science Part II, acidity measurements standing alone can be deceptive. Thus, labeling regulations require that a producer cannot simply state the olive oil’s acidity without providing additional context. That additional context comes in the form of measurements for peroxides, waxes, and ultraviolet absorption.
What are peroxides, and why are they in my olive oil? Peroxides are chemical substances that are formed from the chemical reaction of olive oil with oxygen. Prolonged exposure to air results in an increase in oxidation and rancidity. In short, high peroxide levels indicate a product that has not been properly stored, whether due to defective packaging or failure to reseal a container after use. That’s the reason that all of our oil is sold in resealable containers. To ensure freshness, we use bottles which have been pressure tested to 120 psi.
Peroxides are measured in mil equivalents (mEq) of oxygen (O2) per kilogram (kg). The dictionary tells us that a mil equivalent is “The equivalent of one thousandth; 10^-3 mol, divided by valence.” We hope you understand what that means, because we’re not quite sure. All we know is that extra virgin olive oil must have peroxide levels below 20 mEqO2/kg, and for 2022 ours came back at 4.1 mEqO2/kg, which is really good.
Waxes. Measuring waxes is the simplest way to determine whether you are dealing with a fraudulent product. Waxes do not naturally occur in extra virgin olive oil in any significant amount. Instead, they are formed as the result of extraction by chemical processes. Therefore, if waxes are found in an olive oil in any significant quantity, it is a sure sign that the oil has been blended with a refined olive oil or a pomace oil.
To be considered extra virgin, an olive oil may not have any more than 250 parts per million (ppm) of waxes. Laboratory results confirm that Kollias Olive Oil's 2022 harvest scored a perfect zero.
Ultraviolet Absorption. Another way to determine whether you are dealing with a fraudulent product is through ultraviolet light spectophotometry. Natural oils that are mechanically extracted do not contain fatty acids chains formed by double or triple conjugated bonds. Typically these kinds of bonds are created during rectification, a process in which the oil is mixed with other oils, such as refined oils or particularly old oils. These bonds are not present in pure and freshly extracted olive oils.
One way to find out whether an olive oil has been blended with refined oils (K232) or old oils (K270) is to determine how much ultraviolet light they absorb at wavelengths of 232 and 270 nanometers (nm). These measurements are recorded as K232 and K270, with the K standing for “coefficient of extinction” (again, the science is a bit beyond us).
The K232 test is a particularly delicate indicator of oxidation, especially for oils that have been heated in the refining process. Refining results in formation of double-bond or triple-bond fatty acid chains that also absorb ultraviolet light at wavelengths of 232nm (conjugated peroxides). The K232 test measures this absorption, and if the results show a K value higher than 2.50, you’re probably looking at a refined, adulterated oil. For 2022, our single source extra virgin olive oil scored an excellent 1.5.
Like the K232 test, the K270 test measures fatty acid chains which absorb ultraviolet light at wavelengths of 270 nm (aldehydes and ketones). K270 measurements increase when extra virgin olive oil is not fresh. A high reading suggests a product contains old extra virgin olive oil of a previous year's harvest, or a blend of fresh extra virgin olive oil with older oil of previous harvest. Fresh extra virgin olive oil must have a K value of under 0.22 on the K270 test. For 2022, our single source extra virgin olive oil scored an outstanding 0.113.
The final ultraviolet light test is the Index ΔK. Any score over 0.01 indicates fraud, specifically the blending of an extra virgin olive oil with a non-extra virgin olive oil. For 2022, our single source extra virgin olive oil beat the test by an order of magnitude, coming in at 0.001.
