How to Reuse Olive Oil for Sautéing and Frying

Consumers are increas­ingly aware of olive oil’s health ben­e­fits. While many use olive oil to pan-fry or sauté at home, only a frac­tion of deep-fry­ing enthu­si­asts turn to olive oil.

Still, a grow­ing body of research shows that olive oils are the most bal­anced, safe and healthy fat for both pan-fry­ing and deep-fry­ing.

Moreover, when reusing fry­ing oil more than once, noth­ing is bet­ter than olive oil.

“I do not usu­ally deep fry at home, but should I do that, I would cer­tainly use olive oil, which I com­monly use for all of our house­hold cook­ing,” Guy Crosby, a pro­fes­sor at the Harvard T.H.Chan School of Public Health’s nutri­tion depart­ment, told Olive Oil Times.

One of the rea­sons many shun olive oils for deep-fry­ing is their rel­a­tively higher prices than other com­mon cook­ing oils.

Whether it is canola oil, corn oil or sun­flower oil, most cook­ing oils usu­ally come with a lower price tag than olive oil, let alone the high­est grade: extra vir­gin olive oil.

On top of that, fry­ing oils are cum­ber­some, as rel­e­vant vol­umes are used for deep-fry­ing and need to be ade­quately dis­posed of after use. This, and their price tag, make reusing fry­ing oils a highly sen­si­tive sub­ject.

Why EVOO’s unique pro­file makes it the best deep-fry­ing oil

In the past few decades, many researchers have focussed on how olive oil is affected by fry­ing.

For exam­ple, a 2022 study pub­lished in Food Chemistry found that fry­ing with vir­gin olive oil results in French fries with some of the oil’s healthy qual­i­ties; fry­ing with vir­gin olive oil proved to be more ben­e­fi­cial than using less antiox­i­dant-rich cook­ing oils to fry.

The antiox­i­dants in extra vir­gin olive oil and unique anti-inflam­ma­tory com­pounds such as oleo­can­thal make it the ideal can­di­date for deep-fry­ing.

“Olive oil and extra vir­gin olive oils are cer­tainly used for deep-fat fry­ing, and you can cer­tainly reuse them, as they are some of the most sta­ble fry­ing oils that you can buy,” Crosby said.

When sautéing or fry­ing, all veg­etable oils are sub­jected to mod­i­fi­ca­tion and oxi­da­tion. These reac­tions are mit­i­gated in olive oils because of the high pres­ence of monoun­sat­u­rated oleic acid.

Extra vir­gin and vir­gin olive oils also boast a high vol­ume of antiox­i­dant polyphe­nols, such as tyrosol and hydrox­y­ty­rosol. In dif­fer­ent mea­sures, they show resilience to fry­ing.

Crosby cited a lab exper­i­ment that showed how fry­ing pota­toes in vir­gin olive oil for 10 min­utes at 180 °C (356 ºF) halved hydrox­y­ty­rosol lev­els, which fell to 10 per­cent of the orig­i­nal amount after being reused for fry­ing six times.

On the other hand, tyrosol degraded by only 20 per­cent even after being reused for fry­ing 12 times.

“What hap­pens there is that the antiox­i­dants in vir­gin olive oils pro­tect the fatty acids from oxi­da­tion,” Crosby said.

“While re-use for deep fry­ing will even­tu­ally decrease polyphe­nols and antiox­i­dants found in EVOOs, this will only par­tially affect a cru­cial anti-inflam­ma­tory agent found in EVOO and in vir­gin olive oils only, which is oleo­can­thal,” Crosby said.

Oleocanthal is one of the most inter­est­ing phe­no­lic com­po­nents of extra vir­gin olive oil.

Its impact on health is the sub­ject of many ongo­ing stud­ies. Those stud­ies show evi­dence of highly sig­nif­i­cant effects, from its anti-can­cer prop­er­ties to pre­vent­ing neu­rode­gen­er­a­tive dis­or­ders.

Even if heated for long peri­ods at very high tem­per­a­tures, such as 240 °C (464 ºF) in a lab exper­i­ment, oleo­can­thal only par­tially degrades its bio­log­i­cal activ­ity.

How to safely reuse EVOOs for deep-fry­ing

Reusing extra vir­gin olive oils for deep fry­ing requires the same care when other fry­ing fats are brought into play.

When food is deep-fried, some of its par­ti­cles end up in the fry­ing oil, con­t­a­m­i­nat­ing it. To reuse it more than once, oil should then be care­fully fil­tered. ​“Contamination is a major aspect to con­sider,” Crosby noted.

“Think of what might hap­pen in some fast foods. If you do not ade­quately fil­ter and change what­ever fry­ing oils you are using, if you do not keep it fresh, that can become an issue,” he added, refer­ring to research link­ing exces­sive con­sump­tion of fast foods’ fried serv­ings to heart prob­lems.

Correctly fil­ter­ing deep fry­ing oil before reuse is cru­cial, as this pre­vents those oil’s smoke points from being reduced dra­mat­i­cally after each use.

The smoke point for fil­tered extra vir­gin olive oil is 207 °C (405 ºF), which is well above the deep-fry­ing tem­per­a­ture, which rarely exceeds 190 °C (374 ºF). The smoke point is highly rel­e­vant as triglyc­eride mol­e­cules break apart, and the toxic acrolein alde­hyde is formed above this thresh­old.

“Extra vir­gin olive oil has a rea­son­ably high smok­ing point,” Crosby said. ​“But again, the more any fry­ing oil is used, the more con­t­a­m­i­nated it will be from the food or the mois­ture of the food and more. As food par­ti­cles decom­pose and oxi­dize, the smoke point will decrease sub­stan­tially each time.”

This is also why fil­tered EVOOs have a higher smok­ing point than unfil­tered prod­ucts, as the lat­ter will con­tain olive par­ti­cles.

Keeping track of oxi­da­tion while deep-fry­ing once or more

EVOOs and refined olive oils come with dif­fer­ent price tags. They also bear sig­nif­i­cant dif­fer­ences in their qual­ity pro­files. These dif­fer­ences emerge when con­sid­er­ing deep-fry­ing and olive oil reuse.

Among cook­ing olive oils, extra vir­gin olive oil shows higher sta­bil­ity dur­ing cook­ing or fry­ing due to the sig­nif­i­cant pres­ence of antiox­i­dants.

The oxi­da­tion process leads to the release of spe­cific com­pounds, which can impact health. ​“Oxidation in a deep fat fryer is a sig­nif­i­cant issue,” Crosby said. ​“Vegetable oils other than EVOOs com­monly used for fry­ing, such as soy­bean or canola oils, tend to oxi­dize a lot.”

“The oxi­da­tion prod­ucts have not been thor­oughly proven to con­sti­tute a health haz­ard,” he added. ​“Yet, it is pretty well accepted that such oxi­da­tion prod­ucts are a health risk as they begin to build up.”

“Thanks to its polyphe­nols, EVOO tends to build up much fewer oxi­da­tion prod­ucts, allow­ing it to be reused at least sev­eral times before hav­ing to dis­card it and change it,” Crosby noted.

What about deep-fry­ing with the so-called light olive oils?

Refined olive oils are often sold as ​“light” olive oil, and pro­duc­ers encour­age their use in sautéing and deep fry­ing.

These prod­ucts are usu­ally cheaper than extra vir­gin olive oil. They are meant to bring olive oil to the house­hold with­out the more robust fla­vors usu­ally found in vir­gin or extra vir­gin olive oil (which are pro­vided by polyphe­nols).

“Some of those light olive oils that are usu­ally fil­tered might even have a higher smok­ing point than extra vir­gin olive oil,” Crosby said.

“That is a favor­able char­ac­ter­is­tic when used in a deep fat fryer, but, on the other hand, they lack the polyphe­nols and antiox­i­dants of extra vir­gin olive oil,” he added.

The refined olive oil pro­duc­tion process implies using heat and chem­i­cals which allow the extrac­tion of oil from olives that have already been pressed. ​“Such pro­duc­tion process reduces sub­stan­tially the healthy con­tents,” Crosby said.

“That means that if you switch to the light olive oil, you are los­ing the health ben­e­fits of the high con­tent of polyphe­nols in extra vir­gin olive oil,” he con­cluded.