Background Information

About FryCheck

Background Information

Deep-frying can be traced back to 5,000 BC, and remains a very popular cooking technique worldwide. Deep- frying imparts a crispy texture to food and creates savory flavors as the oil reacts at high temperatures with the food’s surface, coating, or batter. While it is oftentimes thought of as an “unhealthy” way to prepare food, if it is done properly, deep-fried foods retain very little of the oil that they are cooked in.
“Viejafriendo huevos (Old woman frying eggs)”,Diego Velázquez (1599-1660)ca. 1618.
Chemical Composition: Frying oils are most commonly derived from the seeds or fruits of vegetables (e.g. soybeans, palm, sunflowers) and are primarily composed of triglycerides, which consist of three fatty acid molecules esterified to a glycerol unit. The differences among vegetable oils prepared from different sources involve the length and number of double bonds in the fatty acid components. In the example illustrated here, the triglyceride contains two polyunsaturated fatty acids and one monounsaturated fatty acid.
Trigycerides containing fewer double bonds tend to be solids at room temperature, while those with more double bonds tend to be liquids.
Smoke Point: Thefatty acid composition of frying oils is also reflected in their physical properties – including their smoke points, their taste, and their stability in a very hot fryer. The smoke point is the temperature at which hot oilbegins to visibly smoke when heated. The smoke point typically represents the maximum usable temperature of an oil. In general, oils rich in saturated and monounsaturated fats have the highest smoke points and are more resistant to oxidation. Conversely, oils high in polyunsaturated fats degrade more easily.Historically, many chefs have used smoking to determine when to change oil, but this is not a reliable practice.
Oxidation of Frying Oils: The high temperatures used for frying, combined with oxygen, light, salts and water from the food being fried significantlyaccelerate the degradation of frying oils. In the presence of high heat and water, triglycerides hydrolyze to form free fatty acids and glycerol. The fattyacids, especially those present in polyunsaturated oils, further degrade to form an array of oxygenated products including epoxides, carboxylic acids, hydroperoxides, alcohols, aldehydes and ketones. These oxygenated byproducts are collectively referred to as Total Polar Compounds (TPCs). Small amounts of TPCs are not considered unhealthy. Indeed, they can enhance the flavor of fried foods. Fry Life: Since it is one of the costlier kitchen commodities, frying oil is typically reused several times before being discarded. Multiple frying cycles result in more extensive degradation with the rate of degradation (and number of times a batch of oil can be reused) dependent on the oil type, the temperature, and the type of food being fried.Regardless of the initial composition of the oil, multiple scientific studies have concluded that when the accumulated TPCs comprise over 25% of the oil it is no longer healthy and the fried foods are less appealing (TPCs become absorbed by the food or coating – resulting in a greasy product with an off flavor). This point, isoften referred to as the Fry Life of an oil.