In the past, cereal manufacturers incorporated predominantly saturated fatty acids such as coconut and palm oils into their products to reduce the risk of rancidity. Public concern over saturated fat and its relationship to blood cholesterol levels has contributed to increasing use of unsaturated oils and new ways of deterring rancidity. One method of inhibiting rancidity consists of packing such items as potato chips, tortilla chips, and other foods high in unsaturated fatty acids in vacuum packs or nitrogen to prevent contact with oxygen.

To prevent rancidity of the oils and fats themselves, there are several protective measures that can be taken. Vegetable oil bottles should be recapped immediately after use to minimize exposure to oxygen. They are best kept in cool, dry places away from air, light, high temperatures, and exposure to metals such as iron and copper. In warmer climates, they fare better in the refrigerator. Storing a bottle of oil on the shelf near the range, where heat is constantly being generated, is not recommended.

Reducing the consumption of dietary fat may be accomplished by following dietary guides recommending a meal pattern featuring the selection of foods that are lower in fat, especially the saturated type; relying on lower-fat or non-fat cooking methods; and reducing the fat in recipes.

Once overall fat intake is reduced following these guidelines, the next step is to modify the types of fat that are ingested. Monounsaturated fats are preferred over polyunsaturated, which in turn are recommended over saturated fats. For cooking fats, compared to other oils and fats, canola oil contains one of the highest levels of monounsaturated fatty acids. In the same category, olive, avocado, almond, and apricot oils tend to impart more flavor but are more expensive. Safflower oil scores highest in the category of polyunsaturated oils. Saturated fats – coconut, palm, and palm kernel oils and butter – should be avoided according to certain dietary guides.

Butter is often chosen, however, for its unique flavor or by those concerned about the trans fatty acids found in margarines and other partially hydrogenated fats. Although butter and margarine contain approximately the same number of calories (kcal) and grams of fat, the fat in butter is primarily saturated, while that from margarine is more unsaturated. Lard, the saturated fat from swine, is best replaced by vegetable shortening, but even the latter is partially saturated.

Lowering dietary fat may also be achieved in part by selecting a cooking method that does not rely on fat. All of the moist- and dry-heat cooking methods, with the exception of frying, lend themselves to fat-free preparation of foods. Even frying, specifically sauteing and stir-frying, is acceptable if the type of fat is chosen carefully and the amount used is kept to a minimum. Pan-frying and deep-fat frying are the only two methods for which it is essentially impossible to lower the amount of fat used.

Another way to reduce fat in food preparation is to focus on the recipes. The following foods are the main contributors to fat in recipes: meats, dairy products (including whole milk, cheese, cream, ice cream, whipped cream, and butter), commercial fats and oils, avocado, coconut, olives, nuts and seeds. Processed foods such as cakes, cookies, pies, snacks, and others that are made with these ingredients are also high in fat. Many recipes could simply have their fat content reduced or another ingredient substituted without affecting overall quality. Sometimes the fat can be removed altogether. Following the dietary guides will automatically eliminate recipes that are too high in fat and cannot be adequately modified; any meal exceeding 20 grams of fat is probably too high in dietary fat for people consuming three meals a day. Other ways to reduce the amount or modify the type of fat in the diet include:

• Fruit preserves and honey can replace butter on breads.
• Mustard, ketchup, or low-fat salad dressing or mayonnaise may substitute for regular mayonnaise in sandwiches or salads.
• Purees of fruits such as plums, dates, apples, and figs may replace some, but not all, of the fat in recipes for baked products.
• Crumb crusts can replace standard pie crusts.
• Double-crust pies can be converted to one-crust pies, automatically cutting fat by close to 50 percent.
• A nonfat condiment such as salsa, relish, or chutney can replace some of the butter or sour cream toppings on baked potatoes.

Foods should be as free of surface moisture as possible before being submerged in the heated fat. Water causes spattering of hot oil, which can cause burns; it requires more energy to maintain temperatures; it may result in longer frying times; and it causes the fat to break down chemically, reducing its frying life.

Inevitably, particles of food or breading break off or fall through the basket and build up in a deep-fat fryer over time. These food particles should be filtered out daily (or every eight hours of use) or they will darken the oil’s color, lower its smoke point, and reduce its keeping time. On the other hand, excessive filtering introduces oxygen into the oil, resulting in rancidity, gum development, and foaming, the latter observed as a persistent layer of bubbles on the surface.

A frying fat should theoretically stay fresh for several months if it is cooled immediately after use and stored in an air-tight container in a dark, cool place. Refrigeration will also increase its shelf life. Large commercial fryers contain too much fat to be cooled completely and then efficiently reheated, so they are turned down to approximately 225^oF (107^oC). Decreasing the temperature during down time prevents the fat’s breakdown and extends its usefulness.

There is no easy method for determining when oil that has been used repeatedly should be discarded. The first indication that an oil needs to be replaced is that its color and the color of the fried food starts to darken. This transformation takes place soon before the flavor and odor of the oil start to deteriorate. An experienced person can tell by looking at it if the oil needs changing, but food service establishments may purchase a commercial kit that allows anyone to determine an oil’s freshness by checking its color against a standard provided in the kit. A further indication that the oil is too old is that the food fried in it is greasier than normal because of increased oil absorption. Other factors to consider in the decision to discard oil include the type of oil used, the type of foods being fried, the number of times the oil is used, the presence of many particles, excessive foaming or smoking, and the quality of the foods cooked in the oil.

The quality of the fried food product is influenced by conditions other than temperature. It is important to use stainless-steel equipment. Iron, and especially copper or copper alloys such as brass, may increase rancidity. Hoods or exhaust systems above the fryer should be cleaned frequently so that accumulated particles do not drop back down into the fat. Deep, narrow containers are recommended for deep-fat frying, because shallow, wide pans increase the surface area, lowering the smoke points by the greater exposure to air.

The fryer should be filled no more than one-half to three-fourths full of oil. As fat is absorbed by the foods, it should be replaced with fresh fat; but fresh fat should never be added to fat that is rancid, foaming, or dark, because it will not overcome these defects and will itself then deteriorate very quickly.

The freezing point of water is 32^o on the Fahrenheit scale and 0^o on the Celsius scale. Its boiling point at normal atmospheric pressure is 212^o on the Fahrenheit scale and 100^o on the Celsius scale. The boiling point changes slightly with altitude; 1^oF (2.2^oC) must be subtracted for every 500 feet increase in elevation. Other compounds in the water, such as sugar or salt, influence its boiling and freezing temperatures, so all three scales pertain to pure water. Other materials have their own freezing and boiling points.