Rancidity: The Fight Every Oil Eventually Loses

Every antioxidant in olive oil- every polyphenol, every milligram of vitamin E- is fighting the same losing battle against the same outcome: rancidity.
It starts small. Oxygen finds an unsaturated fat and forms a hydroperoxide. Chemists call this primary oxidation, and it's exactly what peroxide value measures. From there it's a slow, patient unraveling toward flat, stale, crayon-like flavor. Every oil gets there eventually. The only real question is how long the fight lasts.

The actual off-flavor you'd taste doesn't come from the hydroperoxides themselves. They're mostly flavorless. It comes from what they break down into next: secondary oxidation products like hexanal. The specific aldehyde behind that stale, cardboard-like smell everyone recognizes instantly but nobody can quite name. Peroxide value catches the crime in progress; your nose catches it after the fact.

Practical version of all this: once a bottle is opened, oxygen exposure resets the clock every time the cap comes off. Good olive oil isn't a pantry item with an indefinite shelf life. Dark storage, a tight cap, and using it within a few months of opening all buy the antioxidants inside more time to keep doing their job.

KORAJE measured a peroxide value of 9.2, under half the legal ceiling of 20. Not a taste description. A measurement of how far into the fight we still are.

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