1How defects are evaluated
The Panel Test (IOC/EU method) is the official sensory analysis for olive oil classification. A group of certified tasters evaluates both positive attributes (fruity, bitter, pungent) and defects — always measured as the "median of defects."
An extra virgin olive oil must have a median of defects = 0 and a median of fruitiness > 0. If even a single defect exceeds this threshold, the oil falls in category: it can no longer be legally called "extra virgin."
2The main defects
Rancid
The most famous defect. It comes from lipid oxidation — the reaction of unsaturated fats with atmospheric oxygen. It develops over time, accelerated by light, heat, and air.
On the nose: smell of stale fat, similar to old butter or oxidized walnuts. On the palate: a persistent aftertaste of "old grease," leaving a dry sensation.
Cause: inadequate storage (light, heat, open container for too long), or poorly stored olives before milling.
Winey-Vinegary
A smell and taste reminiscent of wine or vinegar. It is due to the production of acetic acid, ethanol, and ethyl acetate by fermentative yeasts and bacteria.
On the nose: acidic, winey notes, sometimes sharp like wine vinegar. On the palate: perceived acidity (unlike chemical acidity, this one is tasted!), a sharp sensation.
Cause: fermented olives (piled up too long before milling, in anaerobic silos), or excessive processing temperatures.
Musty-Humid
A characteristic smell and taste of molds and yeasts developed on the olives.
On the nose: typical smell of mold, damp cellar, wet paper. On the palate: earthy aftertaste, rotten mushroom.
Cause: olives with surface mold, stored in excessively humid conditions, or harvested already damaged.
Muddy Sediment (Morchia)
An aftertaste of oil sediment that decants and ferments at the bottom of storage tanks.
On the nose: similar to musty but heavier and greasier. On the palate: aftertaste of fermented grease.
Cause: tanks not cleaned properly between seasons, or oil left in contact with its own heavy sediments.
High-quality olive oil is completely free of defects
In well-made oil—from healthy, rapidly milled, and cold-extracted olives—defects do not exist.
Discover the clean oils in our shop →