Oils

Unlike fats, oils are liquid at room temperature. Most may be used in the same way as solid fats for shallow and deep frying, but may also be used to make salad dressings or simply as a dipping oil. Oils are typically extracted from seeds, nuts and vegetables either by cold extraction or by heat extraction.

Cold extraction oils are usually obtained by pressing and grinding the seeds or fruit with heavy granite millstones or modern stainless steel presses. The resulting oils retain all of their flavour, aroma and nutritional value. Heat extraction methods include expeller pressing, which involves pressing the fruit, nuts or seeds under extreme pressure, generating heat in the process. Although these types of oil retain much of their flavour and aroma, they are not quite as flavoursome as cold pressed oils. Chemical solvents may also be used to extract the oil, which is then boiled to eliminate most of the solvents. Heating the oil to such a high temperature cleanses the oil, but results in a product that has very little of the original flavour, aroma, or nutrients contained in the original seeds or fruit. However, this highly refined oil tends to have a higher smoke point than the unrefined oil (that is, it may be heated to a higher temperature) and has a much longer shelf life.

In general, oils contain a high percentage of unsaturated fat, rather than the saturated fat found in animal fats. Some, such as olive oil, contain high levels of monounsaturated fats, which help to decrease the bad cholesterol in the blood (low density lipoproteins) and help to increase the good cholesterol (high-density lipoprotein). Other oils (such as grape seed oil), contain high amounts of polyunsaturated fats, which helps to lowers the overall cholesterol level, but also reduces HDL (good cholesterol). However, some of these polyunsaturated oils (for example, rapeseed and soya bean oil) also contain omega-3 fatty acids, which are said to reduce the risk of heart disease, lower blood pressure and guard against plaque build-up in the arteries.

In this section, we take a look at the range of oils available from around the world, with a guide to their nutritional information and tips on how best to use them.