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Choosing and Using Cooking Oils
by Don Buscher, MS
Don is a freelance food and health writer based in Asheville, NC. He also analyses recipes for Delicious Magazine.
Although Americans in general may be cooking less, their culinary skills are greatly improving. Gourmet cooking techniques, such as sautéing and stir-frying, have all but replaced the traditional frying practices in many households. Industry has kept up with these new skills by offering an incredible selection of oils. The culinary uses of oils differ from one oil to the next depending upon their fatty acid content, level of refinement, flavor and sensitivity to heat.
Basic Classification of Oils (degree of saturation)
All vegetables oils contain a combination of saturated, monounsaturated and polyunsaturated fatty acids. The predominate fatty acid in an oil or fat determines how it is classified. Most vegetables oils are low in saturated fat with the exception of coconut and palm oil. These oils are rarely available in supermarkets, but are common in many processed foods. Oils high in monounsaturated fat include olive, canola, and peanut oil. These oils are considered heart-healthy oils. Studies have shown that monounsaturated fat lowers LDL ("bad") cholesterol levels without lowering HDL ("good") cholesterol levels.
Oils high in polyunsaturated fat include safflower, sunflower, corn, soybean and sesame oils. They contain some fatty acids that our bodies cannot produce and thus are an essential part of our diet.
Methods of Extraction
Vegetable oils are extracted from seeds, nuts, beans or the fruit of a plant by using a chemical or mechanical extraction process. The kind of extraction process selected determines the quality and nutritional value of the final product.
Most of the inexpensive oils are solvent-extracted. This method is more economical because it extracts over 99% of the available oil. In this process, ground seeds are treated with heat and toxic solvents, such as hexane, a gasoline-like chemical, producing an oil-solvent solution that is heated to about 300˚F to evaporate the solvent.
In the expeller method, a mechanical press is used to squeeze oil out of seed, nut or fruit. Expeller presses create heat, ranging from 160˚F to 203˚F, depending upon the amount of pressure needed to extract the oil. No external heat is applied in the expeller method, thus oils pressed at 160˚F or less qualify as "cold-pressed". A few oils, such as flax, peanut, sesame and virgin olive oil truly are "cold-pressed" oils because their flesh is soft enough to be pressed without generating much heat.
Degree of Refinement
Unrefined oils can be either expeller or solvent extracted. They are simply filtered and bottled with no further processing. Unrefined oils retain the savory flavor of the seed, nut or fruit from which they came.
Refined oils undergo a series of additional processes to remove all substances that may cause strong flavors or colors. These processes include degumming to remove phospholipids, such as lecithin; bleaching to remove pigments, such as beta-carotene and chlorophyll; and deodorizing at 464˚F or higher to remove all odors and unwanted flavors. The end product is an odorless, bland-tasting oil stripped of its phospholipids, minerals, beta-carotene and 30 to 40 percent of its Vitamin E.
Oils with low levels of beta-carotene and vitamin E tend to spoil quickly, so many manufactures add synthetic antioxidants, such as BHA or BHT, to extend their shelf life.
Specialty Grades
Olive oil is unique in that it is graded according to its acid content. Oil from the first pressing of olives with an acidity level of 1 percent or less qualifies as "extra-virgin". It is the most flavorful of the olive oils. Oil with acidity levels between 1 and 3 percent from either the first or second pressing is labeled "virgin". All virgin and extra-virgin oils are unrefined and expeller-extracted. Solvent extraction is required to obtain oil remaining in the pulp residues, which then has to be heat treated and further refined. This oil is labeled "pure". Virgin olive oil is one of the few unrefined oils available in supermarkets; most others need to be purchased through a health food store.
What labels really mean
"Light " on a label means light in color not calories. All oils are pure fat and have the same amount of calories. "No cholesterol" appears on some labels, but that is misleading because no vegetable oils contain cholesterol. Look for "natural" and/or "unrefined" on a label. "Natural" refers to expeller-pressed, unrefined oils. If "unrefined" does not appear on the label, you can be certain the oil is refined.
Nutritional differences between types of oils
There are two fatty acids, omega-6 linoleic acid (LA) and omega-3 alpha-linolenic acid (LNA), that our body cannot manufacture and therefore must come from an outside source. For this reason, omega-6s and omega-3s are called essential fatty acids (EFAs). They are used to make hormones, build cell membranes, and help control blood pressure and blood clotting. The omega-3s also help reduce the risk of heart disease, improve dry skin conditions, enhance brain function and reduce inflammation associated with arthritis.
Polyunsaturated fats are the best sources of the EFAs. Corn, safflower, sunflower, soybean, sesame and pumpkin seed oils are all high in omega-6 fatty acids. Udo Erasmus, author of Fats That Heal, Fats That Kill, discourages the uses of corn oil however because it is often partially rancid. All the monounsaturated fats are low in omega-6 fatty acids.
Only a few polyunsaturated oils contain omega-3s. Flax seed oil contains the most omega-3s (58%), followed by pumpkin seed oil (0-15%), walnut oil (5%) and soybean oil (4%). Of the monounsaturated fats, only canola oil contains a measurable amount of omega-3 fatty acids (11%). Olive oil and peanut oil have virtually none.
Although refined and unrefined oils of the same variety contain similar fatty acid compositions, the high-temperature—over 180˚F—processing of refined oils can damage EFAs, creating high levels of free radicles that can be dangerous to your health. Temperatures above 320˚F cause unsaturated fatty acids to form trans-fatty acids, a type of fat not normally present in oils that can clog arteries and increase the risk of cancer.
Furthermore, unrefined oils contain more vitamin E, chlorophyll and phytosterols than refined oils. Unrefined safflower, sunflower, and corn oil contain the highest amounts of vitamin E, followed by sesame, soybean, peanut and lastly olive oil.
How to best match oils to foods
The particular oil used in a dish can be as crucial to its flavor as the spices it contains. An otherwise bland meal can be exceptional with the appropriate oils. Flavor and stability are the key factors to consider in matching oils with dishes.
Unrefined oils are highly flavored and impart a subtle nutty taste to the foods they are combined with. Theses oils can add incredible flavor to salad dressings, dips, spreads, soups, marinades and pasta sauces. They also nicely complement fish and meat dishes, and add a nutty flavor to cookies, muffins, and quick breads. Refined oils have very little detectable taste that works well in delicately-flavored dishes where the strong flavor of a refined oil might be too overpowering.
Both unrefined and refined polyunsaturated oils are chemically unstable and tend to break down when subjected to high temperatures. If you are heating an oil and it starts smoking, discard the oil and start over. Many of the fatty acids have been destroyed and free radicals (toxic molecules) have been created in the process. Unrefined oils also tend to lose their flavor when heated. Adding these oils at the end of cooking or using them in dishes that don't require cooking best preserves their quality and flavor.
Refined polyunsaturated oils can be used for low to medium heat (200˚F - 350˚F) cooking, like light sautés and sauces, and for low-heat baking. The preferred cooking oils are refined sesame oil and the monounsaturated oils. These oils are quite stable when heated and more suitable for medium to high-temperature (300˚F - 450˚F) cooking.
High oleic safflower and sunflower oils, and refined peanut oil are the best oils for cooking at temperatures greater than 450˚F, such as deep-frying. Butter, coconut oil and palm kernel oil are also used in deep-frying, but are not recommended because of their high saturated fat content.
Monounsaturates
Canola oil has a relatively high smoke point and neutral taste, making it a good all-purpose oil. Its heart protective qualities make it a good choice for medium to high-heat cooking, such as sautéing and stir-frying. It is especially good for baking sweets that need an oil with little flavor.
Olive oil is a favorite ingredient in many salad dressings and Mediterranean dishes. Use "Extra-virgin" to season already cooked foods, or for dipping bread. "Virgin" olive oil is excellent in Italian pasta sauces. "Extra-light" is filtered and somewhat refined, making a more neutral tasting olive oil that is suitable for sautéing and stir-frying.
Peanut oil has a high smoke point and mild peanut flavor. The refined oil is good for popping popcorn, baking, sautéing, frying and deep-frying. It will give deep-fried French fries and tempura a slight nutty flavor. Unrefined peanut oil has a rich peanutty flavor, that is outstanding in Thai and Indian dishes, or drizzled over steamed kale or other greens. It's also delicious combined with soy sauce, grated ginger, minced garlic and onions and used as a marinade or dipping sauce for shrimp and chicken. Make a delectable salad dressing using peanut oil, wine vinegar and grapefruit juice.
Omega-6 Rich Polyunsaturates
Corn Oil is a popular medium heat oil good for baking, sautéing, and stir-frying. It is almost tasteless and better used in dishes where an unrefined oil may be too strong. The unrefined oil has a rich buttery, fresh corn taste that is exquisite in pastries and breads; especially cornbread, as well as in Southwestern and Mexican dishes.
Safflower oil is a bland tasting oil used in many salad dressings and for low to medium heat cooking. The more flavorful unrefined oil adds a pleasant nutty taste to sauces, dressings and desserts. High-oleic safflower oil has a high smoke point and is one of the few oils suitable for deep-frying.
Sesame oil made from toasted sesame seeds has a very dark color and a deliciously strong nutty, smoke-like taste. A few drops will add an immense amount flavor to foods, and is particularly good in Asian and fish dishes or drizzled over steamed vegetables. The toasted oil should not be heated, or only slightly heated. Sesame oil made from raw untoasted sesame seeds has a higher smoke point and is safe for sautéing and stir-frying. It's lighter color and milder flavor also goes well in salad dressings.
Sunflower oil has a very mild flavor. Both the refined and unrefined oils have a low smoke point, and are best limited to salad dressings and dishes cooked on a low heat. High oleic sunflower oil can tolerate high cooking temperatures and can be used for deep-frying.
Soybean oil is the most common cooking oil in the U. S. It is flavorless and has a relatively high smoke point, making it an all-purpose oil suitable for baking, sautéing and stir-frying.
Omega-3 Rich Polyunsaturates
Flax oil is the richest source of omega-3s (58%), making it an excellent choice for non-cooked dishes. Drizzle it over salads, steamed vegetables and cooked grains; add to salad dressings, bean dips, hummus, and cold pasta sauces; or mix with herbs and nonfat yogurt or silken tofu to make a nutritious dip. It is safe to use in baking bread since the internal temperature of the loaf does not exceed 221˚F.
Hemp oil has a well-balanced ratio of omega-3 (20%) and omega-6 fatty-acids (60%). Like flax oil, it is best used in non-cooked dishes. Add to salad dressings, dips, cold pasta and vegetables sauces; or drizzle over salads, cooked grains and steamed vegetables.
Pumpkin oil is a dark green, toasted oil with lots of flavor. It is heavenly when drizzled over steamed vegetables, pastas and salads. The omega-3 content of pumpkin oil varies from 0 to 15%, depending upon the species of pumpkin. Pumpkin oil should not be heated.
Walnut oil is a highly flavored oil that is delightful in salad dressings, chicken salad, and cold pasta sauces. It's also terrific simply tossed with pasta and steamed vegetables, and brushed on grilled meats or fish. It should not be cooked, but can be used for low-temperature baking. It adds a wonderful nutty flavor to quick breads and pastries.
Storing Oils
Heat, light and air cause oils to go rancid (oxidize). All oils should be tightly capped and kept in the refrigerator, particularly polyunsaturated oils as they are less stable than other types of oil. Olive oil is less likely to go rancid because of its high monounsaturated fatty acid content, and can be stored in a cool, dark cabinet. However, excessive light and heat will cause olive oil to spoil too, so it's wise to refrigerate it. Olive oil becomes semisolid when refrigerated, but returns to a liquid after sitting 15 to 20 minutes at room temperature. Transferring oils into dark-colored bottles also helps prolong their shelf-life.
Refined oils will keep 6 months to a year in the refrigerator. Unrefined oils are less stable and will only keep 4 or 5 months, so it is best to purchase them in small quantities. Sesame seed oil contains natural preservatives (sesamol and sesamin) and will keep longer than other unrefined oils. Flax and hemp oils spoil very quickly and need to be used within 3 to 6 weeks. They will kept up to a year however in the freezer.
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