Selecting a cooking oil used to be a case of "vegetable oil, olive oil or butter?". No longer. These days it is easy to find all kinds of fancy oils. This is a mixed blessing — it allows far more flexibility, but makes selecting the best oil for the task a lot harder.

Ultimately, the original three are enough to provide an adequate solution for any kind of cooking. But then, jeans, a t-shirt and a suit provide an adequate solution to clothing. Having access to a few extra oils is a great way of adding a little more variety to food. On the other hand, it's not worth going out and buying a bottle of every kind of oil for home use — there's considerable overlap in styles, and oil doesn't keep forever.

A note on terminology: strictly speaking, an oil is liquid at room temperature whereas a fat is solid. The distinction is often ignored when cooking — butter in particular will melt with very little heat, so is often used as a cooking 'oil'.

Oil Characteristics

Oils can be classified by two characteristics: flavour and smoke point. For a few oils, stickiness and reactivity can also be relevant issues. Finally, some oils are sold with added flavourings.

Flavour

Oils with a strong flavour can significantly alter the taste of the food. Sometimes this is desirable — the distinctive taste of sesame oil is an important part of many oriental recipes. Sometimes, though, strong oils can ruin a meal. When working with delicate fish in particular, the wrong oil can kill the meal's flavour.

Although not strictly speaking a cooking issue, flavour makes even more of a difference when mixing a salad dressing. Here the oil usually forms a significant part of the end flavour, so selecting the correct oil is critical.

Smoke Point

When an oil is heated above a certain temperature, it will start to decompose. The temperature at which this happens is called the smoke point, because most cooking oils will give off nasty smoke when they break up. The smoke point is lower than the flash point, which is where the oil catches fire. None the less, it is extremely important never to exceed the smoke point of an oil. As well as a nasty taste and smell, the smoke from some oils contains various carcinogenic compounds.

For low temperature cooking, the smoke point is largely irrelevant. When frying or oven cooking at higher temperatures it is sometimes a significant issue, and when making a sauté or stir fry it should be a primary concern.

Other Considerations

A few oils are not particularly good at preventing food from sticking to the pan. This can be a problem if food is being fried for more than a few minutes.

Most oils are fairly inert and will not react with food or pans. A few obscure oils have been known to go badly with certain foods and pan surfaces, however — when selecting an uncommon oil, it may be wise to check whether it reacts with anything.

Some oils claim to have various health benefits. Separating the genuine differences from the kooky pseudo-science is rather tricky — chances are, the only way that this is at all relevant is that certain otherwise obscure oils can easily be found in health food stores.

Flavoured Oils

Recently, certain producers have started making oils which come pre-flavoured — popular choices are garlic, lemon, chilli, ginger, basil and rosemary. This is a slightly controversial topic. Personally, I prefer to add flavourings when cooking; others find pre-flavoured oil more convenient. Some things to bear in mind:

  • The smoke point of pre-flavoured oils will be lower than that of the clean equivalent.
  • Pre-flavoured oils will not last as long before they start to go nasty.
  • Some people are concerned about botulism when using flavoured oils. This may be an issue for home made oils, although its significance is debatable, but pre-made oils should contain lots of nasty additives to eliminate any risk. There are plenty of ways of making yourself ill when cooking, most of them far more common than botulism.

Popular Cooking Oils

Now for some of the more popular cooking oils. Note that the smoke points will vary considerably depending upon whether the oil has been refined. There are various tables of smoke points around, all of which are only very rough approximations and many of which are misleading on the issue of refined oils.

Sunflower oil, Vegetable oil, Rapeseed oil, Canola oil
Fairly little taste. Fairly low smoke point.
Butter
Slight taste, usually not noticeable in the end product. Very low smoke point.
Olive oil
Moderate to strong flavour depending upon the style. Medium smoke point.
Sesame oil
Very strong flavour, plays an important part in certain Japanese and Chinese recipes. Medium smoke point. Do not use this oil in salad dressings — it will drown out the flavour of the other ingredients.
Grapeseed oil
Very mild flavour, very high smoke point. It remains slippery for longer than most other oils. Ideal for sautés, making crunchy jacket potatoes and high temperature oven cooking.
Peanut oil
Noticeable flavour, high smoke point. Often used in salad dressings.
Walnut oil
Noticeable flavour, fairly low smoke point. Better for salad dressings than for cooking.
Avocado oil
Noticeable flavour, but not overpowering. Extremely high smoke point. Very viscous — less of this oil is needed when cooking.
Bacon grease
It is rumoured that some people actually use this stuff for cooking. It has a baconish flavour, a very low smoke point and is prone to catching fire. Other variations on this theme include lard, dripping and ghee — these are all fats and aren't particularly good for frying.

If I could only have a single oil, I would go with grapeseed. It's not a conventional choice, but it's not very expensive and the high smoke point and low flavour make it fairly versatile. Others have different opinions — different oils suit different cooking styles. Experimentation is encouraged.