Fat is an important ingredient in many foods because of its functional properties. In many recipes, fat enhances the taste, aroma and texture of the food. It is also digested more slowly than protein or carbohydrates and plays an important role in satiety, providing a sense of fullness after eating.
WHAT IS RANCID OIL?
Rancid oils are a major source of destructive free radicals in our diet. Exposure to air, heat, and light cause oils to oxidize, become rancid, and form free radicals.
Saturated fats are not affected much by oxidation because they are very stable and have a high degree of resistance to oxidation. Monounsaturated fats, since they have a pair of missing hydrogen atoms are somewhat vulnerable to oxidation. Polyunsaturated oils, which are missing several pairs of hydrogen atoms, are very unstable and highly reactive to oxidation.
Signs of Deteriorated Oil
- Oil darkens with use because the oil and food molecules burn when subjected to high/prolonged heat.
- The more you use an oil, the more slowly it will pour. Its viscosity changes because of changes to the oil's molecular structure.
- Loose absorbent particles accumulate as sediment at the bottom of the storage container or are suspended in the oil.
- When smoke appears on the oils' surface before the temperature reaches 190 degrees C (375 degrees F), your oil will no longer deep-fry effectively.- If the oil has a rancid or "off" smell or if it smells like the foods you've cooked in it, it should be discarded.
Prolonging The Shelf-Life of Oil
The longer an oil is heated, the more quickly it will decompose. Avoid preheating the oil any longer than necessary. If you're cooking more than one batch of food, quickly add each new batch, unless time is needed to adjust the cooking temperature. Turn off the heat as soon as you've removed the last food batch from the oil. Cool.
Use a quality deep-fat frying thermometer, even if you're using an electric deep fryer.
Shake off loosely attached break crumbs from breaded food before adding the food to the oil. Loose crumbs and other particles scorch quickly and pollute your oil. Use a small strainer or slotted spoon to remove as many crumbs as possible.
When the oil has cooled enough that it is safe to handle, strain it through paper towels, coffee filters or cheesecloth into its original empty container or a clear glass jar. Do not mix it with unused oil.
Store the oil, tightly sealed, in a cool, dark place or in the refrigerator. The oil may cloud in the refrigerator, but it should become clear again at room temperature with no ill effects.
HYDROGENATED FATS
Hydrogenated fats is one of the fats that is least prone to oxidation, which can lead to rancidity. Hydrogenation is used to convert liquid oils to a semi-solid form for greater utility. For example, vegetable oils are often hydrogenated to produce shortenings or margarines. Hydrogenation also is used to increase the stability of a fat or oil, which is important in cooking and extending a product's shelf-life.All fats, particularly polyunsaturated fats, have a tendency to break down or oxidize when exposed to air. Oxidized fats impart an undesirable rancid flavor and odor. By adding hydrogen molecules, the fatty acids become more stable and resistant to oxidation. This is especially important for fats used in deep-fat frying.
Tips for saving frying oil:
Usually, after frying food such as chicken wings, fish, prawns etc, people used to store the leftover frying oil again to re-use for another time. Frying oil CAN be saved for further frying but it is recommended to do the following:
- Let the oil cool.
- Using a fine strainer, remove any large pieces of debris.
- Using cheese cloth, filter again to remove fine particles of debris.
- Pour into a covered container and refrigerate to prevent rancidity.
-Frying oil can be used 3-4 times before discarding. But refrain from using more than 4 times as rancidity might have occured.
