International trade standards specify that extra virgin olive oil is extracted exclusively from olives, solely by mechanical means, without excessive heating or any chemical processing. Extra virgin olive oil is a natural product that does not need much to be preserved. It contains antioxidants, Nature’s preservatives that extend the oil’s shelf life if stored in a sealed bottle, away from the light and in cool temperature.
Compared to wine making, extra virgin olive oil production is a simpler and faster process. But unlike wine, olive oil does not improve with age. It is at its best when fresh but will unavoidably change over time. Yet the volatile components that give extra virgin olive oil like Morocco Gold its desirable “green notes”, the flavour and aroma that consumer and tasters desire, will eventually disappear over time.
Three basic laboratory assays are required to determine the oil’s grade. They measure olive oil’s attributes related to quality of the olive fruit and its processing and assess the oil’s present state.
From olive fruit to bottled oil
Superior extra virgin olive oil like Morocco Gold is obtained only when harvest, milling and processing of olives are properly managed. Along those steps, there are two naturally occurring and interrelated processes that must be understood as they impact the olive oil’s quality: lipolysis and oxidation. Lipolysis (a form of hydrolysis) begins on the olive fruit as it ripens, and is caused by enzymes present in the fruit, which are later on removed with the vegetation water. Lipolytic enzymes break down major olive oil components and generate free fatty acids, precursors to olive oil change of condition.
Oxidation (more specifically, auto-oxidation) is triggered when the oil enters in contact with oxygen in the air, first during the milling process, and later on during storage in tanks and bottles. Oxidation produces peroxides from some fatty acids. Peroxides are unstable compounds which are further oxidized to yield volatile and non-volatile components that give rise to off-flavours and undesirable aromas in the oil (secondary oxidation). The other form of oxidation, photo oxidation, is usually minor and negligible if the oil is stored in the dark. In brief: lipolysis generates free fatty acids and oxidation causes the formation of peroxides from these fatty acids (primary oxidation), eventually leading to rancidity and degradation of the oil over time (secondary oxidation).
Attaining extra virgin olive oil of superior quality requires minimizing the generation of free fatty acids by hydrolysis and delaying the onset of oxidation. The oxidation process in extra virgin olive oil takes place in three stages: initiation, propagation and termination.
Figure 1: Olive Oil Oxidation
Figure 1 shows how the oxidation of fatty acids in olive oil changes with time. Once the oil has been decanted or centrifuged, the free fatty acid level (or free acidity) will gradually decline while the oil remains in storage. [Declining free acidity is represented in the graph by the down-sloping line from upper-left to lower-right.] During the initiation stage, free fatty acids present in the oil become slowly oxidized, giving rise to small amounts of peroxides. Since peroxides, in turn, decompose into other substances, the overall peroxide level does not increase rapidly. However, when certain levels of peroxides are reached in the oil, a propagation stage ensues during which peroxide levels will rapidly increase, as peroxides beget other peroxides. [Increasing accumulation of peroxides is represented in the graph by the rising left-side of the curve.] During the termination stage, peroxides further decompose giving off numerous off-flavour compounds that humans can detect, even if present at extremely low concentrations—below parts per million. Therefore, even when just a tiny fraction of peroxides degrade into undesirable compounds, the oil will begin to taste rancid. [Rancidity is represented by the lower line rising from the bottom-left to the right of the graph.]
If the quality of the olive fruit was very good and free acidity levels were low when processing the olives, there may be a time lag of up to 3 years before peroxide levels in the oil become problematic (that is, the initiation period is long). But if the olive fruit was spoiled, the temperature during processing was too high or the malaxation time too long, there is an increased risk of reaching higher peroxide levels much sooner, thereby shortening the oil’s shelf life. [Peroxides’ evolution is represented by the bell-shaped curve in the centre of the graph.]
Olive Oil Quality Attributes
The basic olive oil parameters measured analytically are: Free Fatty Acids (FFA), Peroxide Value (PV) and UV absorbance. In combination, they will indicate proper or inadequate handling of the olive fruit prior to milling and assess the oil’s present state of oxidation.
Free Fatty Acids (FFA) or Free Acidity
As mentioned earlier, free fatty acid formation precedes most, if not all oil deterioration. Free acidity levels increase by hydrolysis of the major oil molecules in the fruit (triglycerides) early in the production process, from harvest through milling, while water and plant enzymes are still in contact with the oil. For this reason, milling the olives soon after harvest, and promptly separating oil from vegetation water are critical to maintaining a low initial free acidity level, essential for higher-quality oil.
Free acidity values provide an indication of how the fruit was handled prior to processing and the length of time from harvest to milling. Free acidity is also an early indicator of the potential longevity of the oil. Higher quality oils recently produced, will exhibit very low acidity—it may be no higher than 0.35% in the best extra virgin olive oils (EVOO) like Morocco Gold.
Peroxide Value (PV)
Peroxides, which are flavourless, are generated from the oxidation of polyunsaturated fatty acids in the oil (linoleic and linolenic acids). Peroxides are unstable, usually building up slowly and eventually leading to oil rancidity. The onset of this decay process may be delayed for up to 3 years in good extra virgin olive oil, rich in radical-scavenging antioxidants. But once peroxides are present, rancidity is unavoidable. Peroxide Value identifies the early stages of oxidation. Subsequent oxidation is detected through UV absorbance and by the oil’s sensory properties, which result from the peroxides’ breakdown.
To reduce peroxide levels and therefore delay oxidation of high peroxide oils, blending may be a viable recourse. Otherwise, refining is the only option to eliminate peroxides and remove off-flavor substances. Obviously, the resulting product will not be extra virgin olive oil.
Ultraviolet (UV) Absorbance
UV tests determine the ultraviolet light absorbance measured by shining UV light through the oil at several specific wavelengths. Absorbance at K232 nm (nanometers), K270 nm and Delta K correlate with the state of oxidation by detecting specific oxidized compounds, some generated from secondary oxidation, and also detect possible adulteration with refined oils.
Interpreting The Olive Oil Analysis Results
The standard set of quality tests for grading olive oil includes organoleptic (sensory) tests and the three basic analyses: FFA, PV and UV. The International Olive Committee’s (IOC) olive oil standards specify the precise measurement thresholds to be met for oils to be graded as extra virgin, virgin, and so on. Whenever analytical parameters (FFA, PV, and UV) exceed a given threshold, the oil is classified as the next lower quality grade. But experts agree that a quality EVOO can meet more stringent thresholds than the standard, reflecting the freshness and quality of truly superior oil. The standard FFA threshold is 0.8% acidity, but fresh, high-quality EVOO can certainly achieve FFA values of 0.3 % or lower.
Peroxide Values vary widely over time. Some oils may meet the EVOO’s 20 meq/kg threshold while already showing early signs of rancidity. Experience indicates that high-quality, recently milled oils exhibit peroxide values below 12 meq/kg. Truly excellent oils may have PV as low as 7 meq/kg (9 meq/kg for organic oil). The lower the PV, the more likely the oil’s shelf life will be extended.
Regarding UV absorbance, though the standards call for K232 below 2.5 and K270 below 0.22, superior olive oil will exhibit K232 values below 1.85 (2 for organic oil) and K270 below 0.17. As mentioned before, low values correlate with high-quality oil, as UV absorbance detects early and later states of oxidation.
This olive oil anaylsis provides producers and buyers and ultimately customers with valuable information about the quality of fruit and processing that went into the extra virgin olive oil. That is why we have included the results of our own analysis on each and every bottle of Morocco Gold extra virgin olive oil.