Study conducted by UC Davis Olive Oil Center, 2011.
Our laboratory tests found that the top-selling imported brands of "extra virgin" olive oil sold in the United States and purchased at retail locations throughout California often failed the IOC's sensory standards for extra virgin olive oil. Sensory analysis showed that these failed samples had objectionable descriptors such as rancid and fusty. Sensory analysis is a sensitive tool to analyze olive oil quality and is an essential component of the IOC olive oil standards, but sensory analysis should be supported by gas chromatographic analyses and other analytical methods. It is essential to support sensory evaluations by chemical tests for volatile compounds that are known to be produced by lipid oxidation.
Our chemical tests indicate that the samples usually pass the IOC's chemical tests even when those samples failed two IOC-accredited sensory panels. Chemical confirmation of the negative sensory results were strongest with the German/Australian DAGs and PPP tests, followed by IOC tests for UV absorption. The IOC and USDA standards would be more effective in assessing and enforcing olive oil quality by including the German/Australian DAGs and PPP standards.
Our testing indicated that the samples failed extra virgin olive oil standards for reasons that include one or more of the following: (a) oxidation by exposure to elevated temperatures, light, and/or aging; (b) adulteration with cheaper refined olive oil; and (c) poor quality oil made from damaged and overripe olives, processing flaws, and/or improper oil storage.
This study was performed by the UC Davis Olive Center. Click here to view the entire report.