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All About Cooking Oil

Want to know how cooking oil sizzles and fries? Check out this article for everything that’s worth to know about cooking oil’s shine!

What is Cooking oil?

Cooking oil is a liquid fat derived from plants or animals that finds application in frying, baking, and various cooking methods.

Elevated cooking temperatures can be accommodated by oil, compared to water, resulting in swifter and more flavorful cooking. Furthermore, heat is evenly disseminated, mitigating the risk of scorching and uneven cooking, and on occasion, the oil itself imparts its distinctive flavor. In addition to its cooking utility, the use of cooking oil extends to food preparation and non-heated flavor enhancements, like the creation of salad dressings and bread dips.

At room temperature, cooking oil typically has a liquid state, although certain oils containing saturated fat, such as coconut oil, palm oil, and palm kernel oil, exist in a solid form.

Oils are derived from sources like nuts, seeds, olives, grains, or legumes through extraction methods employing industrial chemicals or mechanical processes.

Health and Nutrition

While it is common for small amounts of saturated fats -such as to be found in coconut oil, palm oil, and palm kernel oil- to be consumed in diets, a significant correlation between high saturated fat consumption and elevated blood LDL concentration, which is a risk factor for cardiovascular diseases.

On the other hand, oils with lower levels of saturated fats and higher concentrations of unsaturated fats, preferably omega-3, like olive oil, peanut oil, canola oil, soy, and cottonseed oils, are generally considered to be healthier.

The U.S. National Heart, Lung, and Blood Institute has recommended the replacement of saturated fats with polyunsaturated and monounsaturated fats. It has identified olive and canola oils as sources of healthier monounsaturated oils, while soybean and sunflower oils are recognized as good sources of polyunsaturated fats.

It is noteworthy that oils derived from cashews and other nuts do not pose a risk to individuals with nut allergies, as oils primarily consist of lipids, and allergic reactions are attributed to surface proteins on the nut.

Moreover, it is worth mentioning that the seeds of most cultivated plants contain higher levels of omega-6 fatty acids compared to omega-3, with certain exceptions. Seeds grown in colder temperatures generally yield seed oils with higher omega-3 fatty acid content.

What are trans fats?

Trans fats, as opposed to other dietary fats, are devoid of essential qualities and do not contribute to the promotion of good health. Their consumption leads to an elevation in the risk of coronary heart disease, as it results in the augmentation of LDL cholesterol levels and a reduction in HDL cholesterol levels. Trans fats originating from partially hydrogenated oils exhibit greater harm compared to naturally occurring oils.

Various extensive studies (1,2) have established a connection between the consumption of substantial quantities of trans fats and the onset of coronary heart disease, and potentially other ailments. Recommendations to limit the intake of trans fats have been issued by the United States Food and Drug Administration (FDA), the National Heart, Lung, and Blood Institute, and the American Heart Association (AHA). In the United States, trans fats are no longer considered “generally recognized as safe,” and their addition to foods, including cooking oils, is prohibited without special authorization.

How to store cooking oil

All oils are subject to degradation when exposed to heat, light, and oxygen. In order to postpone the onset of rancidity, the vapor space in the storage container is often shielded with a layer of an inert gas, typically nitrogen, immediately after production. This protective process is referred to as tank blanketing.

In conditions that are cool and dry, oils exhibit greater stability. Nevertheless, they may undergo a thickening effect, although they will return to a liquid state when left at room temperature for a short duration. To mitigate the deteriorating influence of heat and light, oils should be extracted from cold storage for only the necessary period of use.

Refined oils that possess high monounsaturated fat content, like macadamia oil, can be preserved for up to a year, whereas those with a high polyunsaturated fat composition, such as soybean oil, maintain their quality for approximately six months. Rancidity assessments have indicated that walnut oil has a shelf life of roughly three months, a duration notably shorter than the “best before” date displayed on labels.

Conversely, oils characterized by a high saturated fat content, such as avocado oil, enjoy relatively extended shelf lives and can be securely stored at room temperature. This is facilitated by their low polyunsaturated fat content, which contributes to their inherent stability.

How oil reacts to heat?

The transformation of the properties of cooking oil occurs rapidly when subjected to heat. Oils that are typically considered healthy at room temperature can undergo a detrimental shift when exposed to high temperatures, especially with repeated heating. Fatty acids with higher levels of unsaturation are more prone to oxidation during exposure to air so the selection of a cooking oil should take into account its heat tolerance and match it with the intended cooking temperature. Additionally, the practice of changing frying oil several times per week is advisable.

Palm oil, unlike canola oil, corn oil, linseed oil, soybean oil, safflower oil, and sunflower oil, contains a higher proportion of saturated fats. This property enables palm oil to endure deep frying at elevated temperatures and resist oxidation, especially when compared to highly polyunsaturated vegetable oils.

The following oils are suitable for high-temperature frying owing to their high smoke points:

  • Avocado oil
  • Mustard oil
  • Palm oil
  • Peanut oil (referred to as “groundnut oil” in the UK and India)
  • Rice bran oil
  • Safflower oil
  • Olive oil
  • Semi-refined sesame oil
  • Semi-refined sunflower oil

Less aggressive frying temperatures are frequently employed. An ideal frying oil possesses a mild taste, smoke and flash points of at least 200 °C (392 °F) and 315 °C (599 °F), respectively, with maximum levels of 0.1% free fatty acids and 3% linolenic acid. Oils with higher linolenic fractions are avoided due to the risk of polymerization or gumming, characterized by an increase in viscosity over time. Notably, olive oil demonstrates resilience against thermal degradation and has served as a frying oil for thousands of years.

Smoke point

The smoke point of cooking oils generally varies according to the oil’s refinement process. Higher smoke points result from the elimination of impurities and free fatty acids. The presence of residual solvents remaining from the refining process may diminish the smoke point.

  • The smoke point
    is characterized by “a continuous wisp of smoke.” It signifies the temperature at which oil commences burning, resulting in a burnt taste in the prepared foods and the deterioration of the oil’s inherent nutrients and phytochemicals.
  • The flash point
    is the temperature at which oil vapors can ignite but are insufficient to sustain a continuous flame. (527–626 °F / 275–330 °C)
  • The fire point
    is the temperature at which hot oil generates adequate vapors to catch fire and burn. As the duration of frying increases, all of these temperature thresholds decrease, with their fluctuations being more dependent on the acidity of the oil rather than its fatty-acid profile.
FatQualitySmoke point
Almond oil221 °C430 °F
Avocado oilRefined271 °C520 °F
Avocado oilUnrefined250 °C482 °F
Beef tallow250 °C480 °F
Butter150 °C302 °F
ButterClarified250 °C482 °F
Castor oilRefined200 °C392 °F
Coconut oilRefined, dry204 °C400 °F[64]
Coconut oilUnrefined, dry expeller pressed, virgin177 °C350 °F[64]
Corn oil230–238 °C446–460 °F
Corn oilUnrefined178 °C352 °F
Cottonseed oilRefined, bleached, deodorized220–230 °C428–446 °F
Flaxseed oilUnrefined107 °C225 °F
Grape seed oil216 °C421 °F
Lard190 °C374 °F
Mustard oil250 °C480 °F
Olive oilRefined199–243 °C390–470 °F
Olive oilVirgin210 °C410 °F
Olive oilExtra virgin, low acidity, high quality207 °C405 °F
Olive oilExtra virgin190 °C374 °F
Palm oilFractionated235 °C455 °F
Peanut oilRefined232 °C450 °F
Peanut oil227–229 °C441–445 °F
Peanut oilUnrefined160 °C320 °F
Pecan oil243 °C470 °F
Rapeseed oil (Canola)220–230 °C428–446 °F
Rapeseed oil (Canola)Expeller press190–232 °C375–450 °F
Rapeseed oil (Canola)Refined204 °C400 °F
Rapeseed oil (Canola)Unrefined107 °C225 °F
Rice bran oilRefined232 °C450 °F
Safflower oilUnrefined107 °C225 °F
Safflower oilSemirefined160 °C320 °F
Safflower oilRefined266 °C510 °F
Sesame oilUnrefined177 °C350 °F
Sesame oilSemirefined232 °C450 °F
Soybean oil234 °C453 °F
Sunflower oilNeutralized, dewaxed, bleached & deodorized252–254 °C486–489 °F
Sunflower oilSemirefined232 °C450 °F
Sunflower oil227 °C441 °F
Sunflower oilUnrefined, first cold-pressed, raw107 °C225 °F
Sunflower oil, high oleicRefined232 °C450 °F
Sunflower oil, high oleicUnrefined160 °C320 °F
Vegetable oil blendRefined220 °C428 °F

What is Deep Frying?

In the process of deep frying, two primary objectives are achieved. First and foremost, the moisture within the food is extracted. As soon as the food makes contact with the hot oil, a reaction ensues, leading to the formation of bubbles. These bubbles represent water pockets that swiftly transition into vapor, rising from the food, ascending through the oil, and ultimately escaping into the surrounding environment. The higher the frying temperature, the more vigorously these bubbles emerge.

Simultaneously, the Maillard reaction takes place. During this reaction, proteins and carbohydrates undergo degradation and recombination, resulting in the development of the brown hues and flavors that are commonly associated with well-fried foods.

How to deep fry?

To prevent foods from acquiring a tough and fibrous texture during the frying process, they are frequently coated with a protective insulating layer of batter or breading. This results in a harmonious combination: tender, steamed interiors and an outer layer that is crisp, brown.

Interestingly, the popular belief that lower oil temperatures lead to increased oil absorption by foods is unfounded. In reality, the extent to which a piece of fried food absorbs oil is directly linked to the quantity of moisture that is expelled, which, in turn, is influenced by the cooking temperature and the final cooking temperature. The higher the frying temperature, the greater the quantity of oil absorbed by the food.

Yet, the perception of greasiness intensifies when frying temperatures are lower. Soggy fried foods, which retain a mixture of oil and residual water in their coating, yield a sensation of softness and oiliness on the palate, even though their actual oil content is lower than that of properly fried food.

To dig deeper check out: All About Deep Frying

Does oil freshness matter?

The degree of freshness in oil significantly influences its hydrophobic properties. As it’s widely known, oil and water exhibit an aversion to mingling, and this phenomenon is pivotal in the effectiveness of deep frying. Placing a food item into a vessel of hot oil results in minimal oil absorption, at least until a sufficient amount of moisture has been expelled from the food.

The progressive deterioration of oil leads to a reduction in its hydrophobic character. Initially, this can be advantageous. Oil with fewer hydrophobic molecules can have closer contact with foods, facilitating a slightly more efficient frying process. This is where the wisdom of those experienced tempura chefs becomes relevant—adding a small portion of aged, degraded fry oil to a new batch can enhance its performance.

However, as this degradation persists, the oil gradually loses its hydrophobic qualities, eventually infiltrating the food at an accelerated rate. This intrusion leads to an unwanted greasiness and the loss of the food’s crisp texture.

At this point, the oil requires replacement. Several telltale indications of aged oil include the presence of foam on the oil’s surface, an incapacity to attain frying temperatures without generating smoke, and a dark, unclean appearance accompanied by a musty, fishy scent.

How many times frying oil can be used?

In food service settings, frying occurs as needed, resulting in fluctuating levels of activity throughout the day. Depending on the menu and local eating habits, fryers are typically utilized at their maximum capacity for several hours daily, used intermittently for a few hours, and remain inactive for the remainder of the time. The intermittent operation of fryers is the primary cause for the periodic need to dispose of and replace frying oil. During periods of idleness and low production, the oil undergoes greater thermal and oxidative stress compared to when actively used for frying. If fryers were continuously operated and the oil consistently filtered, the need for discarding frying oil would be significantly reduced.

Frying Equipment

When frying at home, the oil is more prone to degradation compared to frying in a restaurant setting. The reason behind this lies in the heating setup. In a professional restaurant-grade deep fryer, the heating components are elevated above the bottom of the oil reservoir. This design creates a zone of relatively cooler oil at the very bottom, positioned below the heating elements. Consequently, any tiny food remnants that detach during the frying process settle at the base of the chamber, beneath these heating elements.

Conversely, with a home arrangement, we typically employ a pot or a wok situated over a stovetop burner. Food particles descend to the bottom of the pan, making direct contact with the heat source, where they burn and infuse their flavor into the oil, expediting its deterioration.

Regrettably, there’s no practical way to circumvent this predicament unless we opt to invest in a dedicated electric deep fryer designed for home use. For those who frequently engage in frying, this could be a worthwhile consideration.


As a general guideline, the greater the quantity of particulate matter introduced to the oil, along with the fineness of these particles, the more rapid the oil’s degradation becomes. When it comes to the residue left behind after frying, battered foods such as onion rings or uncoated items like French fries produce minimal debris. On the other hand, breaded foods like chicken cutlets shed crumbs that disperse into the oil when the food is immersed. In the case of foods coated with flour, such as the fried fish sandwiches in question, a substantial number of particles are introduced.

Thus, while oil employed for cooking battered foods may endure for a dozen or more cooking sessions, oil utilized for flour-coated foods may undergo a breakdown after merely three to four uses.


When it comes to battered and breaded foods, the inner composition is of minor significance, as it does not establish direct contact with the oil. However, for foods cooked without any coating, the kind of food involved can influence the overall condition of the oil. Vegetables typically undergo frying with minimal impact on the oil, leaving behind a negligible residue. Conversely, fatty meats such as chicken wings or bacon release fat during the frying process. This fat has the potential to blend with your frying oil, contributing to a slightly accelerated deterioration of the oil.

Oil Type and Temperature

Various oils possess distinct compositions concerning their relative quantities of saturated and unsaturated fats, as well as other solid components. These factors impact their frying characteristics and the temperature ranges they can endure. Typically, refined oils like most peanut, canola, vegetable, and corn oils have a higher heat tolerance compared to unrefined oils like extra-virgin olive oil or most sesame oils. It’s not that frying in extra-virgin olive oil is impossible; it’s just that it will degrade much more swiftly than a refined oil, and it may even struggle to reach the necessary frying temperature without generating smoke.

The most suitable oils for frying are typically those rich in saturated fats, such as peanut oil, vegetable shortening, or lard. Not only do they possess the lengthiest durability, but they also yield the crispiest outcomes.

How to Clean Oil


  1. Employ a skimmer to eliminate any floating particles and large debris that may be lurking within the pot.
  2. Strain the oil through a fine mesh strainer into a clean, dry pot. Dispose the layer of soiled, flour-laden oil at the pot’s bottom, if any.
  3. Cover the pot containing the strained oil to shield it from dust and allow it to cool entirely.
  4. Pour the oil into a storage container then seal the container securely and store the oil in a cool, dry location.


  1. Employ a skimmer to eliminate any floating particles and large debris that may be lurking within the pot.
  2. Strain the oil through a kitchen towel lined mesh strainer into a clean, dry pot. This will take time and requires the oil to be hot which carries the risk of burn injuries. Dispose the layer of soiled, flour-laden oil at the pot’s bottom, if any.
  3. Cover the pot containing the strained oil to shield it from dust and allow it to cool entirely.
  4. Pour the oil into a storage container then seal the container securely and store the oil in a cool, dry location.


  1. After deep-frying, let the cooking fat reach room temperature or slightly warmer.
  2. In a small pot, measure half a cup of water for every quart of used oil. Sprinkle one teaspoon of powdered gelatin per half cup of water and allow the gelatin to hydrate for a few minutes.
  3. Heat the water until it simmers (this can be done on the stovetop or in the microwave), stirring until the gelatin dissolves. Stir vigorously and constantly, then pour the gelatin/water mixture into the soiled oil. The mixture should appear quite cloudy and reasonably uniform at this stage.
  4. Cover the pot and place it in the refrigerator (or transfer the mixture to a separate container before refrigeration) and allow it to rest overnight.
  5. The following day, pour the oil from the top of the pot or container into a separate clean, dry pot.
  6. Discard the gelatin disc that remains. The clarified oil is now ready for use.

When the clarified oil is used again it may start to produce slight bubbling. This is perfectly normal. Gently swirl the pan as it bubbles to aid in releasing any residual water droplets. It will eventually settle down and become suitable for frying.

How to Prolong the Oil’s Lifespan?

  1. Utilize a Thermometer! Overheating the oil represents a swift and straightforward technique for inducing its breakdown into an unsuitable state. Conversely, insufficiently heating the oil before adding food to it will extend the duration during which the food remains immersed. This, in turn, increases the likelihood of particles dislodging from the food, potentially shortening the oil’s lifespan.
  2. Maintain Cleanliness! Maintain a fine mesh strainer near your pot while frying food, and use it periodically to cleanse the oil by capturing and disposing of any fragments of batter or breading that may have separated from your food.
  3. Opt for Battered Foods or Uncoated Vegetables. Battered foods will introduce considerably fewer impurities to the oil compared to breaded or flour-coated foods. Uncoated items like French fries or sweet potato fries introduce even fewer impurities.

Naturally, despite all these recommendations, numerous variables exist that can influence the condition of the cooking oil. The most reliable indicator for determining when to replace or reuse the oil is our own sensory perception.

When it emits foam or has a rancid odor, it should be discarded. Otherwise, simply strain, store, and ready to be used again.


  • Cooking oil is a liquid fat derived from plants or animals that finds application in frying, baking, and various cooking methods.
  • Unsaturated fats are healthy.
  • Saturated fats should consumed in moderation.
  • Cooking oils should be kept under their respective smoking point for extended use and health reasons.
  • Cooking oil can be reused given it’s adequately cleaned and stored.

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