The American Chemical Society’s Reactions YouTube chan­nel has released a video explain­ing the chem­istry behind olive oil and why it is a good kitchen sta­ple. The video goes into how mol­e­cules and antiox­i­dants in the oil help keep you healthy, the dif­fer­ence between oil vari­eties, how to use the oil, and how to store it.

There are hun­dreds of vari­eties of olive oil, and it takes over a thou­sand olives for one liter of high-qual­ity olive oil, the video states. Olives har­vested at dif­fer­ent points in the sea­son also pro­duce dif­fer­ent fla­vors. Lower qual­ity oils are extracted using chem­i­cal sol­vents like hexane, but the best oils (like vir­gin and extra vir­gin oil) are cold pressed using only mechan­i­cal processes. Extra vir­gin olive oil has to meet high-qual­ity taste stan­dards, and have no defects due to oxi­da­tion or fer­men­ta­tion. It is the most fla­vor­ful, but also the most expen­sive of olive oil vari­eties.

Oleic acid is a major com­po­nent of olive oil which shows up as part of a larger mol­e­cule called a triglyc­eride. Sloppy har­vest­ing and extrac­tion tech­niques can lead to triglyc­erides break­ing up to form free fatty acids, which means a higher acid­ity and a lower score on the qual­ity scale.

Olive oil is also rich in monoun­sat­u­rated fatty acids, which pump up the rate at which cells pull bad cho­les­terol out of the blood­stream. It is also rich in antiox­i­dants, called plant phe­nols (like hydrox­y­ty­rosol) and vit­a­min E. The body uses these antiox­i­dants to keep free rad­i­cals (which cause cell dam­age) in check. The antiox­i­dants give olive oil its pep­pery taste.

Olive oil enhances the fla­vor of foods. Some of the taste and antiox­i­dants are lost in high tem­per­a­tures, but you can safely use olive oil in fry­ing, saute­ing and bak­ing (up to 400 degrees Fahrenheit). Extra vir­gin olive oil shines the most in cold dishes where you get more from its taste.

How the oil is stored is impor­tant. This is because olive oil does not age well. Light and heat degrade the oil over time and make it ran­cid due to increased oxi­da­tion with its con­tin­ual expo­sure to the air. This breaks down the fatty acids in the oil into per­ox­ides that decom­pose into alde­hy­des and ketones, which are respon­si­ble for unpleas­ant fla­vors and odors.

The antiox­i­dant con­tent is also reduced over time. To keep the qual­ity of the olive oil for longer, it can be pro­tected by stor­age in a dark bot­tle or stor­ing the bot­tle in a cool, dark space. Looking for a har­vest date on the bot­tle can also help to ensure fresh­ness. It is advised to use up the oil in six weeks after open­ing.

Dan Flynn from the UC Davis Olive Center says: “A really good oil should have a fla­vor rem­i­nis­cent of some­thing that’s grown out in a grove, and it should have this grassy or maybe a fruity fla­vor. An oil that’s not very good would remind you more of some­thing that you’ve stored in your garage for a long time.” Flynn rec­om­mends buy­ing olive oil accord­ing to fresh­ness rather than the price tag.


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