Whether pressed from nuts, fruits or vegetables, they make a good meal. A superior oil can make a dish, an inferior oil, or the wrong type of oil, can break it.
Corn oil on a salad is a no-no, olive oil is perfect. Sesame oil drizzled over a Chinese dish adds mystery, where a glug of coconut oil would add only saturated fat.
Oils are fats which are normally liquid at room temperature, differentiating them from the (mainly animal) fats which are solid at room temperature.
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All plants contain oil, but the parts of plants which contain commercially viable quantities are usually the seeds, beans, nuts, and fruit (the word oil actually comes from the word olive).
Throughout history different societies have had their favored sources, as well as their favored methods of extraction. The ancient Egyptians pressed oil from radishes (if you think getting blood from a stone is hard, try getting oil from a radish) and the ancient Syrians cultivated olives for oil as early as 3000 BC.
Other oils have a more recent culinary history. Walnut oil, for instance, has a longer history in the cosmetics industry than in the kitchen and grape seed oil was only created during World War I, when other oils became scarce in France.
Despite what many people believe, vegetable oils are not necessarily any better for you than animal fats. The proportions of saturated to unsaturated fats in oils vary dramatically from one type to another.
Of the fats in coconut oil, which is widely used in biscuit manufacturing, 91 percent are saturated, while palm kernel oil, used in many processed and fast foods (including those which proudly proclaim that they only use "healthy vegetable oils") has 81 percent saturated fats.
On the other end of the scale, of the fat in sunflower oil, only 14 percent is saturated, while only 10 percent of the fat in safflower oil is saturated. All oils and fats, regardless of their saturated or unsaturated status, contain the same number of calories.
A diet high in saturated fats has been shown to increase the amount of cholesterol in the blood, a risk factor in the development of cardiovascular disease, so people trying to lower their cholesterol levels should try to be certain that the "healthy" vegetable oil they are consuming is not laden with hidden saturated fats.
The terms saturated and unsaturated (comprising polyunsaturated and monounsaturated) describe the chemical composition of the fats in a particular oil. Fatty acids are made up of chains of carbon atoms, linked to hydrogen atoms.
When all the carbon atoms are fully linked with hydrogen atoms, the fat is said to be saturated. When some of the carbon atoms are free, the fat is unsaturated. Some normally unsaturated vegetable oils, such as those used in margarine and shortening, have hydrogen atoms added during processing, in order to create a solid fat, which is easier to transport, which can be spread rather than poured, and which tends to be more chemically stable than liquid fat.
The more unsaturated an oil is, the more prone it is to oxidize and turn rancid. Light and salt accelerate the process, which is why oil should be stored in the dark and why salt should never be added to food before it is fried, if the oil is to be re-used later
Most oils are a rich source of Vitamin E and essential fatty acids, but apart from this, the only thing they contribute to the diet is taste, texture and calories.
Among the less common oils which have found their way into the cuisines of various nations are almond oil and apricot kernel oil (both excellent with salads), evening primrose oil, cottonseed oil, mustard oil (used primarily in Indian cooking), avocado oil and hazelnut oil.
Generally, the nut oils are not suitable for deep-frying. Indeed, many oils tend to break down at high temperatures and develop peculiar flavors.
Nut oils are usually quite expensive, partly because the demand is smaller but also because the amount of oil by weight in the nuts is usually relatively small, but since they are used mainly in small quantities, in salad dressings and for basting, the investment is worthwhile.
Nut oils are made from roasted nuts which have been pressed to extract the oil. Nut oils oxidize easily, and should be stored in tins, rather than in plastic or glass. Oils should be kept in a dark, cool place.
Walnut and hazelnut oils are both subtle and delicious. Other commercial varieties of nut oil include almond oil and, more rarely, a vividly green pistachio oil.
The process of extracting oil from vegetable seeds is actually more complex than the method of making nut oil. The seeds are cracked, heated and pressed, then residue oils are extracted using solvents. The solvent is then evaporated to leave behind the crude oil.
Most oils then require rather extensive refining to remove color, taste and smell.
No wonder the oil which ends up on the supermarket shelf is so bland and uniform (have you ever had peanut oil which actually tasted like peanuts?). In many cases, freshly pressed oil from the same plant has to be added to the refined stuff to give it some taste.
Sesame oil is used, a few drops at a time, to impart a rich, nutty flavor and aroma to many Asian dishes. It is commonly added at the last moment, after the food has been cooked and just before it is served.
With summer fast approaching, this might be the time to try out a few different oils on seasonal salads.
A hazelnut oil vinaigrette is simple to make and will store well in the fridge for a week or so. Mix half a cup of fresh hazelnut oil in a screw-top jar with a tablespoon of balsamic vinegar and the same quantity of red wine vinegar, a pinch of salt and a grind or two of black pepper. Shake well. Pour over a salad made from lettuce, small, tender spinach leaves and some sliced, raw mushrooms. Toss well, sprinkle with chopped hazelnuts.