Properties of Fats and Oils in Cooking that You Should Know

Not all fats are the same. The more refined an oil, the higher the smoke point. That's because refining removes the impurities that can cause the oil to smoke.

Did you know that a fat is no longer good for consumption after it has exceeded its smoke point and has begun to break down?

What is the Difference Between Fats and Oils?

Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides: triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure and composition. Although the words "oils", "fats", and "lipids" are all used to refer to fats, in reality, fat is a subset of lipid. "Oils" is usually used to refer to fats that are liquids at normal room temperature, while "fats" is usually used to refer to fats that are solids at normal room temperature. "Lipids" is used to refer to both liquid and solid fats, along with other related substances, usually in a medical or biochemical context, which are not soluble in water. The word "oil" is also used for any substance that does not mix with water and has a greasy feel, such as petroleum (or crude oil), heating oil, and essential oils, regardless of its chemical structure.

Fats are solid at room temperature. This is the reason why a stick of butter can be left out of the refrigerator and remain relatively solid. Oils are liquid at room temperature. If oils are refrigerated, they may become semisolid and cloudy.

Types of Fats

Saturated Fats

Saturated fats are mainly animal fats and are solid at room temperature. These fats include butter, cheese, whole milk, ice cream, egg yolks, lard and fatty meats. Saturated fats raise blood cholesterol more than any other food you eat. By using the right oils and fats for the right reasons, you can preserve the healthful benefits. Your foods will not only taste their best, but also be healthy.

Unsaturated Fats

These fats can come from both animal and plant products. There are three (3) types:

Monounsaturated Fats - Usually come from seeds or nuts such as avocado, olive, peanut, and canola oils. These fats are liquid at room temperature.

Polyunsaturated Fats - Usually come from vegetables, seeds, or nuts such as corn, safflower, sunflower, soybean, cotton seed, and sesame seeds oils. These fats are liquid at room temperature.

Trans Fatty Acids - Trans fats are produced when liquid oil is made into a solid fat, such as shortening or margarine. This process is called hydrogenation. Trans fats act like saturated fats and can raise your cholesterol level.

Liquid oils and other vegetable fats are about 85 percent unsaturated fats. Generally, the more unsaturated the fats or oils, the healthier they are. In comparison, animal fats are about 50 percent saturated fat and 50 percent unsaturated fat. On the whole, the fat in beef and lamb is more saturated than the fat in poultry and pork. An advantage of saturated fat in cooking is that it tends to be stable, which means that it is less likely to become rancid or deteriorate when it is exposed to metal, oxygen or water. Since poultry and pork have less saturated fat than beef and lamb, these two protein foods may deteriorate faster.

Uses of Fats and Oils in Cooking

A very important use of fats or oils in cooking and baking is in emulsions, the blending of dissimilar ingredients—often into creamy mixtures. In the example of the vinaigrette salad dressing the egg yolk (a common emulsifying agent) helps to break down the oil into tiny droplets that are suspended throughout the vinegar, which yields a creamy consistency. Other emulsions include butter, cream, ice cream, margarine and salad dressings. Béarnaise sauce, hollandaise and mayonnaise are sauces that are created by emulsions. Other emulsifiers include lecithin in crystal or liquid form (in fact, egg yolks are about one-third lecithin), gelatin, mashed potatoes, meat extract, mustard, skim milk and starch “paste.” The trouble with emulsions is that they tend to be unstable. If an emulsion separates, then a dressing or sauce may be whisked back into suspension.

Fats melt when exposed to heat, which means they slowly change from a solid to a liquid state over time. The fact that fats melt and do not instantly turn into liquids makes them versatile ingredients in food product development, cooking and baking. Some fats can eventually turn into gases, much like liquid evaporates into air, but it takes a considerable amount of heat for this to happen.

Fats can decompose, which is unlike deterioration. When fats decompose, they break down into noticeable gas. This is called the smoke point of fats. The smoke point varies among fats and oils; it is wise to select a fat or oil one with a high smoke point that is suitable for hot, sustained cooking to help prevent a change in food flavor.

Fats and oils with fewer free fatty acids tend to have higher smoke points. These include some vegetable oils, such as canola or safflower oils. Animal fats, fresh fats and refined oils tend to have more free fatty acids and thus lower smoke points. These include butter, coconut oil and lard. If a fat has impurities, the smoke point will be lower, which means it will smoke faster. The size of the pot or pan also makes a difference in the smoke point. A wider pot or pan with greater exposure to air lowers the smoke point, which means the fat or oil may decompose faster than one with less exposure.

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In cooking, when the fat or oil reached its smoke point it begins to break down to glycerol and free fatty acids, and produce bluish smoke. The glycerol is then further broken down to acrolein which is a component of the smoke. It is the presence of the acrolein that causes the smoke to be extremely irritating to the eyes and throat. The smoke point also marks the beginning of both flavor and nutritional degradation. Therefore, it is a key consideration when selecting a fat for frying, with the smoke point of the specific oil dictating its maximum usable temperature and therefore its possible applications. For instance, since deep frying is a very high temperature process, it requires a fat with a high smoke point.

The smoke point for an oil varies widely depending on origin and refinement. The smoke point of an oil does tend to increase as free fatty acid content decreases and degree of refinement increases. Heating oil produces free fatty acid and as heating time increases, more free fatty acids are produced, thereby decreasing smoke point. It is one reason not to use the same oil to deep fry more than twice. Intermittent frying has a markedly greater effect on oil deterioration than continuous frying.

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Considerably above the temperature of the smoke point is the flash point, the point at which the vapors from the oil can first ignite when mixed with air. The following table presents smoke points of various fats and oils:

Types of Fats and Oils Smoke Points (°Fa)/ °C

Fat and Oil	Quality	Smoke Point
Almond oil		420°F	216°C
Avocado oil	Un-Refined, Virgin	375-400°F	190-204°C
Avocado oil	Refined	520°F	271°C
Butter		250–300°F	121–149°C
Canola oil	Expeller Press	375-450°F	190-232°C
Canola oil	High Oleic	475°F	246°C
Canola oil	Refined	400°F	204°C
Castor oil	Refined	392°F	200°C
Coconut oil	Virgin (Unrefined)	350°F	177°C
Coconut oil	Refined with stabilizers	450°F	232°C
Corn oil	Unrefined	352°F	178°C
Corn oil	Refined	450°F	232°C
Cottonseed oil		420°F	216°C
Flax seed oil	Unrefined	225°F	107°C
Ghee (Indian Clarified Butter)		485°F	252°C
Grapeseed oil		420°F	216°C
Hazelnut oil		430°F	221°C
Hemp oil		330°F	165°C
Lard		390°F	192°C
Macadamia oil		413°F	210°C
Mustard oil		489°F	254°C
Olive oil	Extra virgin	375°F	191°C
Olive oil	Virgin	391°F	199°C
Olive oil	Pomace	460°F	238°C
Olive oil	Extra light	468°F	242°C
Olive oil, high quality (low acidity)	Extra virgin	405°F	207°C
Palm oil	Difractionated	455°F	235°C
Peanut oil	Unrefined	320°F	160°C
Peanut oil	Refined	450°F	232°C
Rice bran oil		490°F	254°C
Safflower oil	Unrefined	225°F	107°C
Safflower oil	Semi refined	320°F	160°C
Safflower oil	Refined	510°F	266°C
Sesame oil	Unrefined	350°F	177°C
Sesame oil	Semi refined	450°F	232°C
Soybean oil	Unrefined	320°F	160°C
Soybean oil	Semi refined	350°F	177°C
Soybean oil	Refined	460°F	238°C
Sunflower oil	Unrefined	225°F	107°C
Sunflower oil	Semi refined	450°F	232°C
Sunflower oil	Refined	440°F	227°C
Sunflower oil, high oleic	Unrefined	320°F	160°C
Tallow (Beef)		420°F	215°C
Tea seed oil		485°F	252°C
Vegetable shortening		360°F	182°C
Walnut oil	Unrefined	320°F	160°C
Walnut oil	Semi refined	400°F	204°C

Smoke points are approximate because oils differ within the same type of oil,

such as olive (extra-virgin, pomace and virgin) and whether or not the oil is refined.

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References:

Bockisch, Michael. 1998. Fats and Oils Handbook. Champaign, IL: AOCS Press. ISBN 0-935315-82-9.

Culinary Institute of America. 1996. The New Professional Chef (6th ed.). John Wiley & Sons.

Detwiler, S. B.; Markley, K. S. 1940. Smoke, flash, and fire points of soybean and other vegetable oils. Oil & Soap. doi:10.1007/BF02543003.

Morgan, D. A. 1942. Smoke, fire, and flash points of cottonseed, peanut, and other vegetable oils. Oil & Soap.

Wolke, Robert L. 2007. Where There's Smoke, There's a Fryer. The Washington Post.

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Eat saturated fats moderately. Keep healthy and happy cooking! :-)