While it is definitely true that fats and oils carry flavor molecules and conduct heat for cooking, they start breaking down at smoke point. The smoke point of an oil or fat is the stage when it stops shimmering (sign of oil readiness), and starts producing smoke during cooking. At this point, the oil is starting to break down due to overheating. What exactly occurs here is that the fatty acids are released from the glycerol forming into longer polymers that create the unpleasant, bitter or burnt taste. Furthermore, the glycerol reacts with oxygen with a high temperature, forming water and acrolein. Acrolein is an unsaturated aldehyde. It can irritate soft tissues and may cause dizziness, nausea, and headache.

Knowing the smoke point of oils is essential— it saves you from cooking food that is not supposed to taste burnt or bitter. Plus, it minimizes the production of free radicals (reactive chemicals that damage cells) as a result of overheating. Below are the smoke point of some of the common cooking oils for your reference.

Smoke point of common cooking oils

What affects the smoke point of fats and oils?

As you may have already noticed, fats and oils smoke or burn at different temperature. And it depends on several factors, including the fat or oil’s composition, the refinement level of the oil, and the condition of the cooking set up (volume or amount of oil, container size, etc..).

There are 3 main types of fatty acids: saturated, monounsaturated and polyunsaturated. Among these three, more saturated fats tend to decompose faster. This is why butter, which is naturally rich in saturated fats (50%-63%) smokes (at 302 °F) quicker than most types of fats. For a better picture, a refined corn oil, which is only 13% saturated fats can have a smoke point of around 446 °F (230 °C). Safflower oil, which contains around 75% polyunsaturated fats and 12% monounsaturated fat, has one of the highest smoke points.

Another thing that makes butter not ideal for certain cooking method, particularly for sautéing, is its lactose content. Although it only contains trace amount of lactose, it readily burns when heated. When sautéing, what chefs do is remove the protein (milk solids) and water, leaving only fat—or clarified butter. Clarified butter has a smoke point of 482 °F (250 °C).

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Basically, less refined oils have lower smoke points. These oils contain more impurities such as minerals, enzymes, free fatty acids, and other impurities that have a tendency to burn faster. For this reason, unrefined oils are better used in low heat applications. Moreover, unrefined oils turn rancid more quickly, and are less shelf life stable than their refined counterparts. If stored properly, most unrefined oils last for 3 to 6 months.

Which oil to go for?

When choosing oil or fat, smoke point is just one of the few factors to consider.

Generally, you would want to go for fat or oil that has a high smoke point, especially for cooking food that require high heat. Frying require a cooking temperature between 350 °F (177 °C) and 375 °F (191 °C). Peanut oil, almond oil, and safflower oil have high smoke points. Oils with a high smoke point are ideal for stir-frying and deep drying. The higher the smoke point, the better.

What is the flavor requirement of the food? If you want the oil to impart a mild flavor to fried food, you can not go wrong with olive oil. Olive oil is typically a mix of refined and unrefined oil. Extra virgin olive has a lower smoke point than the regular olive oil. With a smoke point of 320 °F (160 °C), it is not suitable for frying, but is used best for drizzling over vegetables or as a base for salad dressing. While oils like peanut oil may have a high smoke point, its mild and nutty flavor usually is retained even after cooking.

If you want an oil that are healthier, opt for an unrefined one. Unrefined oils not only retain the natural flavors, but the enzymes, nutrients and mineral as well. However, again, they have low smoke points, so they are better used for minimal heat cooking or food that do not require cooking like salads or vegetables. To make sure the oil is unrefined, read the label and look for words such as “unrefined”, “virgin”, or “cold-pressed”.

Also go for an oil that contain more unsaturated fats. They are called “good fats” for a good reason— beneficial for the heart and overall health. Extra virgin olive oil contains the highest amount of monounsaturated fats. Aside from having a high smoke point, peanut oil, avocado oil and safflower oil are rich in oleic acid, an unsaturated fat.

Reusing of oil and free fatty acid level

It is totally fine to reuse cooking oil for a few times. However, it is a good idea to know when to discard used oil. Set a limit when using used oil. Cooks Illustrated recommends to use oil only 3 to 4 times for breaded and battered foods, while use oil for up to 8 times at least, if used for cleaner foods like potato chips.

Repeated cooking will accumulate the free fatty acids in the oil. Free fatty acids (FFA) are the products of hydrolysis of oils and fats during cooking. The more the oil is reused, the higher the FFA levels, and the lower the smoke point. Specially refrain from using used oil for cooking food that requires high cooking temperatures. Oils and fats impart that unpleasant bitter taste in food as soon as they hit their smoke point.

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How would you like to call the sixth basic taste—fat or oleogustus? Back in grade school, we were only taught four basic tastes, namely sweet, bitter, sour, and salty. It was until 1990 when umami (or savory) became an official basic taste. Although unlike the other tastes, the Japanese-discovered umami taste went through hardship before being widely recognized. This is because umami was initially thought to be just a flavor, not a taste. Today, scientists believe a sixth taste exists—and is called oleogustus. Difficult to pronounce? You could say fat as well because oleogustus is the latin word for “a taste of fat” (“oleo” means fatty or oily + “gustus” means taste).

To be considered a primary taste, oleogustus, like the other basic tastes, has to satisfy several criteria. A chemical stimulus has to be there that activates the taste buds. From the receptor, the certain taste signal is sent to the brain, which furthers identifies it. And lastly, a physiological response occurs in the body, such as increase salivation.

The discovery of taste receptors for fat in rodents’ tongue

Taste Receptors or “Taste Buds” are cells found in the oral cavity, but are more prominent in the upper surface of the tongue. Traditionally, there were only 4 tastes—sweet, bitter, sour, and salty—that activate the taste receptors in the tongue. In 2000, a team of neuscientists discovered a modified mGluR4, the first tastebud receptor for umami. This solidified umami’s status as the official fifth taste. What about oleogustus?

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Most of us believe that the sensation of fat has been in the texture (like creaminess and smoothness). This happens because of triglycerides, the form of fat our diet consists majority of. But triglycerides do not have any effect on our taste buds. Which in this case does not make fat a basic taste. While taste is based on one sensation, flavor is a combination of sensation (smell, texture, and expectation).

However, in 2005, a group of researchers led by Philippe Besnard from the University of Burgundy in France discovered that the tongue of rodents has taste receptors for fat. That receptor is CD36 or platelet glycoprotein 4. To confirm that CD36 in the tongue really does detect fat, the team studied rodents that were normal or had the gene for CD36 “knocked out”, shutting down or inactivating the taste receptor.

They found that the normal rats and mice showed preference for fatty food when offered. The “knocked out” or CD36-deficient rats and mice did not, indicating that CD36 doees detect fat.

Are fat receptors in the human tongue?

There are many people who love eating fatty foods. In the US, over a third of the population is obese, partly because of the natural attraction to fatty foods. Well, this is despite the well-known fact that excessive fat intake may affect our health in a bad way.

Like that of rodents’, the human tongue apparently has that same receptor for fat. In 2011, researchers at Washington University School of Medicine in St. Louis confirmed the existence of CD36, a potential fat receptor in humans. As first reported on Journal of Lipid Research, the main goal of the research was to understand how fat perception in food might influence what foods to eat and the quantities of fat consumption. The study found individual variability in how people sense fat. Specifically, obese people with a specific CD36 gene have a specific ability to detect fat in a solution. The team studied 21 individuals considered obese (with a BMI of 30 or more). Some of them had a genetic variant that allowed them to produce more CD36. While some produce less, some are in between.

According to Dr. Nada A. Abumrad, one of the authors, one potential reason for individual variability is that as people consume more fat, they become less sensitive to it, requiring more intake for the same satisfaction, as confirmed through a series of taste tests. Abumrad first identified CD36 as the protein responsible for the uptake of free fatty acids. The researchers concluded that people can taste fat, the same way we taste saltiness and sweetness.

Scientists confirm oleogustus (fat) as the sixth basic taste

So far, the three identified free fatty acid receptors are CD36, GPR120, and GPR40. While all these three are present in rodents, the human tongue produces GPR120 and GPR40 at relatively lower levels. With that said, CD36 is implicated as the leading candidate for taste receptor signaling in humans.

In 2015, a study was done at Purdue University in Indiana wherein 102 panelists were given cups containing one of the basic tastes. During the tests, panelists wore nose clips to prevent discrimination of long chain fatty acids from blank solutions. They grouped the cups according to taste— sweet, bitter, sour, salty, umami and fatty. Other sensory attributes including appearance, odor, and texture were controlled for. At first, they easily identified sweet, sour, and salty; but identified the cups of fatty mixture as bitter due to their unpleasant bitter-like taste. This unpalatable taste is similar to oleic and linoleic acid, in terms of intensity. But this suggested that fat taste receptors interact predominantly with long chain fatty acids.

With a new experiment, the panelists grouped together cups of bitter, umami and fatty mixtures. This time, they grouped the cups of fatty mixtures and distinguished them as separate from the rest. This just shows that the fatty acids evoke a unique sensation that satisfies one of the criteria required for the basic tastes.

With all the date gathered, the study concluded that:

These data added to the totality of evidence on “fat taste” now provide a comprehensive body of evidence supporting the existence of another basic or primary taste quality for selected fatty acids (fat taste), whose oral activity should thus be considered when examining the health consequences of fatty acid signaling.

The sixth taste or not (yet)?

To end, the researchers suggested that the new basic taste be named oleogustus or “taste of fat.” Treating fat as a separate and unique taste will help in food product development (such as low-fat foods), clinical practice (such as management of appetite and taste disorder), and public health policy (proposing dietary recommendations).

Although scientists say there is indeed a sixth taste, in terms of acceptance, oleogustus may actually need more time to be accepted widely. Yes, sure the people of science themselves are pushing it. But more experts believe that further research is necessary for wider recognition. It is much similar to umami, which was first identified in the early 1900s in Japan, but only accepted as a basic taste nearly a century later.

Other reference:

J. J. Provost, K. I. Colabroy, B.S. Kelly, M. A. Wallert, The Science of Cooking: Understanding the Biology and Chemistry Behind Food and Cooking, John Wiley & Sons, Inc., 2016

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