Lard, which is the fat from swine, was the major shortening in use in the early 1900s. Tallow, like lard, is an animal fat but it is derived from beef cattle or sheep. Because both are from animal sources, they are primarily saturated fat. They cannot be used for their shortening power in food preparation without first being rendered (melted down); for commercial use, the rendered fat is then deodorized.

Antioxidants are often added to lard to increase shelf life. Lard produces poor textures in cakes and icings, so it is used primarily in pastry pie crusts, commercial frying, and regional cooking.

Interesterification Process

Lard was largely replaced by the shortenings that appeared on the market in the 1950s, but lard usage increased again in the 1960s when the process of interesterification was introduced. Certain fats, such as cocoa butter substitutes and lard, have unacceptable textures until they are modified by interesterification. Lard is naturally too grainy and soft at room temperatures, but becomes extremely hard when refrigerated. Interesterification creates a smoother-textured lard with a slightly higher melting point, which allows the lard to retain its shape at room temeprature. Another food application dependent on interesterification is emulsifiers, which are incorporated into numerous processed foods to improve the functionality of a fat.

Hydrogenation is a commercial process that makes fats and oils more solid, allows them to be heated to higher temperatures before smoking, and increases their shelf life or that of the foods coated with them. The process of hydrogenation is facilitated with the aid of a metal catalyst (nickel, copper, platinum, or paladium) and the presence of pressure and heat. The catalysts are removed after the process is completed. The degree of hydrogenation, or the number of hydrogen atoms added, determines the firmness of the final product.

Through this process, vegetable oils may be convered to spreadable hydrogenated shortenings or margarines. Too much hydrogenation, however, will cause the product to become brittle and hard. In addition to affecting plasticity, hydrogenation contributes to making pie crusts flaky, puddings creamy, and processed foods stay on the shelf longer.

One of the side effects of hydrogenation is that more trans than cis configurations are created at the double bonds. The benefits to a higher concentration of trans fatty acids are a rise in the fat’s melting point, increased solidity, and lengthened shelf life. The long-term health effects of trans fatty acid intakes have yet to be determined, however. Among other health risks, trans fatty acids have been reported to increase the risk for heart disease.

Some vegetable oils, when stored in the refrigerator, do not stay completely liquid. The cooler temperatures may result in cloudiness from the crystallization of certain fatty acids that have a higher melting point than their neighboring fatty acids. This cloudiness may be eliminated by winterizing the oil – a commercial process that lowers the temperature of the oil, allowing the fatty acids with higher melting points to crystallize so that they may be filtered out. Commercial salad dressings and “salad oils” are usually made with winterized oil. Unwinterized vegetable oils that have crystallized in the refrigerator are perfectly edible and will revert to their clear character if allowed to come to room temperature.

The higher amounts of saturated fats in coconut, palm, and palm kernel oil, popularly known as the “tropical oils”, made them popular in the past with the food industry for use in cereals, candy, baked items, chocolate coatings for ice cream bars, pressurized whipped toppings, dog and cat food, and other products requiring a long shelf life. Since they contain fewer double bonds, these saturated fats do not break down as easily, nor do they become rancid as fast as unsaturated fats do when subjected to oxygen, heat, and light.

Tropical oils received negative publicity, however, when the consumption of saturated fats was linked to an increased risk of heart disease. As a result, many food manufacturers and even some fast-food enterprises have switched from tropical oils to vegetable oils for frying. Tropical oils are still used for some confectioneries, such as chocolate coatings for ice cream bars, because they become firm but melt quickly in the heat of the mouth.

Olive oil, which is considered a specialty oil, is more expensive than most other vegetable oils. Despite its higher price, olive oil consumption has increased among health-conscious consumers because of its high monounsaturated fatty acid content (78 percent). Unrefined olive oil are also popular in Italian dishes and salad dressings for their full flavor.

Following Italian law, olive oils are classified according to acidity: the lower the acid content, the better the grade. Extra Virgin is the best (less than 1 percent acid content), followed by Virgin (between 1 and 3.3 percent). Extra Virgin and Virgin olive oils are produced from cold pressing. The result is a high-quality oil with a strong olive flavor and a greenish tint from the presence of chlorophyll pigments. Oil labeled only “olive oil” is a blend of refined olive oil and Virgin olive oil, resulting in a lower acidity but also less intense flavor and color than either Extra Virgin or Virgin olive oil.

“Light” or “extra-light” olive oil is a refined oil made to be lighter in color than corn or safflower oil, and almost as mild. In the United States, olive oils labeled “olive oil” or “pure olive oil” account for 70 percent of all olive oils sold. Price does not always reflect quality; olive oils are best judged by whether or not they have a clear, deep color (usually, but not always, green) and a distinct olive aroma and flavor. In Extra Virgin olive oil, some of the compounds contributing to its flavor and aroma are volatile and are lost when heated, so it is best used in cold salad dressings and as a final flavoring to a dish. Milder olive oils are preferred for sauteing.

An oil called Olive-Pomace oil is produced less expensively by extracting the oil from olives through both cold pressing and the use of solvents. The resulting oil is refined and then blended with Virgin olive oil to improve its taste, odor, and color. Olive-Pomace oil may not be called “olive oil”.

Many different types of oils are available for food preparation purposes, and the type of oil used depends on the desired outcome. The first factor to consider when selecting an oil is its flavor or lack thereof. The bland, mild flavor and heat stability of soybean, corn, and safflower oils make them ideal for frying. Cottonseed oil, however, is the leading choice in food service operations for frying potato chips and for producing baked goods and snacks, because of its low risk of developing and imparting off-flavors and its relative low price. Canola oil is the light, clear oil of rapeseed; it has a bland flavor and high monounsaturated fatty acid content. Rapeseed originally contained high levels of erucic acid and glucosinolates, which, in large amounts, were found to cause cancer in laboratory animals. New genetic varieties, however, contain minimal amounts of these substances and the FDA has allowed the sale of canola oil.

Many refined oils are without any distinguishing characteristics, while unrefined, cold-pressed oils, such as peanut and olive oils, have the full flavor of the plants from which they were pressed. When choosing peanut or olive oils, it is important to be aware of a wide variance in quality and character. Because their flavors are distinctive, these oils must be used carefully in foods. Peanut and sesame seed oils are more costly than many others, but their unique flavors make them the oils most commonly used in Chinese stir-fry dishes. Refined peanut oil is less expensive and is very heat stable, making it ideal for high-heat sauteing and frying. Peanut oil’s flavor is preferred by some snack food manufacturers for their products.

The available vegetable oils are derived primarily from soybeans, rapeseed (canola oil), sunflower seed, corn, cottonseed, and safflower seed. Fruit oil sources include the avocado, coconut, palm kernel, palm, and olive. Oil differ dramatically in their taste, color, and texture, depending on their source and method of extraction.

Extracting and Refining Oils

Oils are obtained from their plant sources through a process that involves both extraction and refining. Extraction of oils is done by either mechanically pressing the seeds against a press, called cold pressing, or chemically removing the oil from the seeds with solvents. Specialty, full-flavored, cold-pressed oils are often consumed unrefined, but most commercially produced oils are extracted by the use of heat and solvents.

When the goal is a neutral, clean-flavored oil, the oil is purified or refined after extraction to remove impurities such as water, resins, gums, color compounds, soil, and free fatty acids. If these compounds are not removed, they adversely affect the oil’s flavor, color, clarity, smoke point, and shelf life. For example, free fatty acids detract from the oil’s flavor and reduce the temperature to which an oil can be heated without smoking. Refining, which results in oil that is 99.5 percent pure, consists of five steps: degumming, neutralizing, washing and drying, bleaching, and deodorizing.

• Degumming – Certain impurities in oil form gums when combined with water. These are removed by adding hot water to the oil and spinning it at high speeds to separate the oil from the gums.
• Neutralizing – Free fatty acids are removed by adding an alkaline medium to convert the fatty acid to an insoluble soap, which settles to the bottom of the neutralizing tank. Newer methods use a centrifuge to separate the major layers according to specific gravity.
• Washing / Drying – Traces of soap created by the neutralizing process are removed by washing the oil with water. The water is drained, and the oil is dried under a vacuum.
• Bleaching – Colored matter in the oil is removed by adding absorbent materials, such as fuller’s earth or activated carbon. The absorbed colored matter is then filtered out.
• Deodorizing – Volatile compounds – aldehydes, free fatty acids, hydrocarbons, ketones and peroxides – which contribute off-odors are removed by passing steam through the heated oil.

Shortenings are plant oils that have been hydrogenated to make them more solid and pliable. Soybean oil is the major source of hydrogenated shortening and serves as a common frying oil. In the manufacture of shortenings, the soybean oil is hydrogenated until it reaches a solid consistency and then whipped or pumped with air to improve plasticity and give it a white color. Many shortenings are also superglycerinated, making them ideal for baking applications where a solid fat is needed, especially for flaky pastries and cakes containing more sugar then flour.

Margarine

During the Napoleonic Wars, the short supply and rationing of butter led Napoleon III to organize a contest to find a suitable butter replacement. And so it was that in 1869, a French pharmacist and chemist, Hippolyte Mege-Mouries, won the contest by developing oleomargarine. During World War II, when a law prevented the coloring of food products, margarine was introduced to United States consumers. It was unappetizingly lard-like and flat white in color. Eventually the law was repealed, and yellow margarine is now a staple in the North American market.

Standard stick margarine must contain at least 80 percent fat, about 16 percent water, and 4 percent milk solids. Contrary to popular belief, regular margarine contains as many calories (kcal) as butter, though the fat sources differ, and lower fat versions are available. Margarine may be made from soy-bean, corn, safflower, canola or other partially hydrogenated vegetable oils. In addition, margarines usually contain: cultured skim milk; emulsifiers such as lecithin; mono- and diglycerides; preservatives such as sodium benzoate, potassium sorbate, calcium disodium EDTA, isopropyl citrate, and citric acid; vitamins A and D; flavorings, usually diacetyl; and food colorings, usually annatto and/or carotene. Diacetyl is added to margarine for flavoring because it is largely responsible, in addition to short fatty acids, for butter’s characteristic flavor.

Available types of margarines include whipped margarine, light blends of margarine and butter containing about 60 percent fat, diet or reduced-calorie (kcal) margarine, which has a higher water content, and imitation margarines identified as “vegetable oil spreads”. Imitation margarines average half the fat of regular margarines.

Butter is made from the cream of milk, with 10 cups (2.5 quarts) of milk required to generate one stick (1/4 pound) of butter. Butter contains about 80 percent milk fat, no more than 16 percent water, and 4 percent milk solids. Salt and coloring additives such as extract of annatto seed or carotene may or may not be added.

As cream converts to butter, dramatic changes occur, because milk is an oil-in-water emulsion, which reverses to a water-in-oil emulsion in butter. Methods of making butter start with cooled cream, which is stirred or, in commercial operations, centrifuged to expel water from the cream. The mechanical agitation breaks the phospholipid membranes around the fat globules, causing the milk fat to escape and lump together. This causes the fatty portion to separate out as a soft, yellowish solid; these are granules of butter the size of corn kernels. Liquid drained from the process is collected and called buttermilk, a tangy tasting, opaque, reduced-fat milk by-product. The butter granules are washed and then churned at slower speed until they are mixed into a smooth, homogenous paste. Any remaining water is drained, and salt is sometimes added at this point for flavor and to act as a preservative. In commercial dairies, the process is begun with a cream that is concentrated up to 80 per-cent fat, and then further concentrated to 98 percent. It is first pasteurized to destroy pathogenic bacteria, cooled, and then recombined with the milk solids and water.

Once it is formed, commercial butter is divided into blocks that are individually wrapped, usually in waxed paper, to prevent odor absorption from other foods. Butter bought at the market has usually been cut into quarter-pound segments and rewrapped, and is sold in wrapped or boxed half-pound or one-pound packages. Grading is voluntary on the part of the processor and is based on the butter’s texture, flavor, color, and salt content.

Butter can be purchased in a number of forms. Taste options are sweet cream butter, with or without added salt, and cultured butter, which has been acidified by lactic bacteria. A popular variant in texture is whipped butter, which is lighter in weight than regular butter and easier to spread because it has been aerated with air or nitrogen gas. Its lower density results in butter with half the calories (kcal) – 50 rather than 100 calories (kcal) per tablespoon – of regular butter on a solid volume, unmelted basis. More of the whipped than the regular butter may be needed, however, to get the equivalent flavor and color. Another type of butter, called compound, composed, or flavored butter, is a softened butter mixed with one or more flavors, such as garlic, lemon, honey, wine, herbs, or nuts.

One of the newer forms, powdered butter, is made by removing the fats in natural butter and chemically treating, drying, and combining it with various ingredients – whey solids, maltodextrins, guar gum, corn syrup solids, and color additives. Powdered butter can be reconstituted with hot water and used in food service establishments to add flavor to vegetables, sauces, soups, and baked products. It is lower in calories (kcal) and cholesterol than natural butter.

Regular butter, or whole butter, must be specially treated before it can be used in certain types of food preparation involving high heats, because its milk solids burn very easily. Butter so treated, called clarified butter (ghee in Indian cuisine), is almost 100 percent fat. It is easily obtained by melting butter over low heat, allowing it to cool until the heavier, cloudy-looking milk solids have settled out, and gently pouring off the clear liquid portion. The smoke point of clarified butter is much higher than regular butter.

Sometimes regular butter is preferred, because the tendency of its milk solids to burn can also have a positive effect in food preparation. It allows the nuttier-flavored brown butter, or Beurre Noisette, and black butter, Beurre Moir, to be made by heating butter over low heat until it turns the desired color.