Fats come to us from many sources - animal and plant - and thus can have very different properties. Luckily, when cooking, only a few are important:



Flavor. Though the fats themselves are generally odorless, they carry with them a variety of chemicals (or lack of them) that can vary between the strong flavor of unrefined palm oil to the bland flavor of canola oil, or from the subtly sweet flavor of coconut oil to the grassy richness of a good quality tallow. Unfortunately, flavor is a terribly subjective (and complicated) beast, and so it is impossible to properly discuss it here.

Viscosity. A measure of how "thick", or liquid, the fat is when melted, it is important to the ability of fats to prevent foods from sticking to pans, and changes how the food feels in the mouth. It is primarily affected by how big each molecule of fat is, expressed as the chain length: long chain lengths mean high viscosity oils which flow slowly and coat surfaces thickly.

Melting Point. The temperature that the fat melts at. This is important if the dish is to be served (or prepared) cold, or if the melting point is higher than the temperature of the mouth: if the fat solidifies, the food feels greasy, and many sauces and dressings break. Melting point is influenced by the percentage of saturated fat and how big the average chain length is: saturated fats and long chain lengths give us fats with high melting points.

Smoke Point. Different oils will begin to smoke at different temperatures.

Chemical Reactivity. Fats can be oxidized by the air, especially at high temperatures, which damages flavor and is bad for health. For these reasons, this article suggests not cooking with (poly)unsaturated oils, which are more reactive than other fats, at high temperatures or for long periods of time.;
, In different foods and cooking methods, the role of any included fat varies, and thus your selection criteria will be different:



Pan-Frying, Stir-Fry, Sauteing. Other than flavor, the most important considerations are viscosity and reactivity; ideally, you will choose a viscous fat (to prevent the food from sticking and burning) which is highly saturated (so that it doesn't oxidize). It is also important to pick a fat which will not smoke at the high temperatures involved.

Deep Frying is rather forgiving, but prefers a nonreactive oil (so that it doesn't oxidize). Depending on preference, you may want to use a viscous oil (which will coat the fried food thickly), or a thin oil, to minimize the fat content of the cooked food.

Hot Soups and mixed into Baked goods, only the flavor matters.

Applied to the outside of baked goods, flavor still usually dominates, but reactivity is a potential consideration, due to the high surface temperatures.

Salad Dressings, Mayonnaise. It is vital that the food stay warmer than the melting point of the fat, or the emulsion will break, leaving you with two nasty layers rather than a creamy sauce.
 An incomplete list is provided above, but feel free to apply these basic criteria:


If your food sticks, use a more viscous fat.
If your oil smokes, use a fat with a higher smoke point.
If you are cooking at a high temperature and/or for a long time, use a nonreactive (saturated) fat.
 Often, you'll need to make a compromise, in which case there are a few options:


Mix different fats together to average their properties. For instance, mix some tallow into your coconut oil to increase the viscosity while still keeping the fat mixture liquid in the mouth.
Add your flavorful, but delicate or reactive, fats after most of the cooking is done.
Learn the characteristics of fats.
Know the cooking method you are going to use and select the fat accordingly.
Determine the important characteristics for your cooking method.
Find a fat with the properties you need.
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