Frying
Cooking of food in oil or fat
From Wikipedia, the free encyclopedia
Frying is the cooking of food in oil or fat.[a][2] Similar to sautéing, pan-fried foods are generally turned over once or twice during cooking to ensure that the food is evenly cooked, using tongs or a spatula, whereas sautéed foods are cooked by "tossing in the pan".[3] A large variety of foods may be fried. Frying is a dehydration process which involves the transfer of mass and heat. Different chemical changes take place during the frying process such as protein denaturation, starch gelatinization, surface browning, rapid water evaporation and oil absorption.[4]
History
Frying is believed to have first appeared in Ancient Egyptian cuisine during the Old Kingdom, around 2500 BC.[5]
There is evidence of frying dating to c. 1500 BC in India, when ghee was used to fry appam.[6] In China, the Book of Rites describes a Zhou dynasty-era recipe for fried rice and fat from a wolf's breast. It is hypothesised that stir frying emerged in field kitchens in the late Han dynasty, but evaded the literary record due to its informal nature.[5] In Leviticus, a distinction is made between baked bread and bread fried in a pan with oil.[7]
In Europe, frying pans begin appearing in Norwegian grave goods in the seventh century.[8] Frying is mentioned in the Wife of Bath's Tale and a reference is made to fried eggs in Don Quixote in the 14th and 17th centuries respectively.[7]
Process
When in contact with oil heated to 150–200 °C (302–392 °F), food undergoes heat and mass transfer.[9] The food's water content reaches boiling point and begins to vaporise, creating pores in its cell walls which enable it to absorb oil.[10]
As heat exposure is greater on the surface of the food in direct contact with the oil, water vaporisation occurs more quickly. This dehydration effect causes a crisp crust to form which protects the centre of the food against further oil absorption.[10] The crust browns due to the formation of melanoidins caused by caramelisation and the Maillard reaction. The food's starch content gelatinises, causing it to soften; the surface contains less water and retains its crisp crust.[9]
Frying is complete when all water content in the food vaporises.[10] When a fried food reduces in temperature below 100 °C (212 °F), water vapour inside condenses and internal pressure drops, causing oil absorption into the food via a vacuum effect.[10]
Techniques
Deep frying
In deep frying, food is submerged in hot oil or fat so that all sides are cooked simultaneously.[11] A deep fryer or chip pan may be used, or, in an industrial frying operation, a pressure fryer or vacuum fryer. One method for preparing food for deep frying involves battering or breading, which adds colour and crunch to its surface.[11] French fries, doughnuts, cong you bing, and tempura are common deep-fried foods.[12][13]
Health effects
A 2021 meta-analysis found that the highest category of fried food consumption compared to the lowest is associated with a 3% increase in the risk of all-cause mortality, as well as with a 2% increase in the risk of cardiovascular mortality.[14] Compared to participants with a low intake, those who ate the most fried food had a 37% increased risk of heart failure, a 28% increased risk of major cardiovascular events, and a 22% increased risk of coronary heart disease.[14] The risk of stroke, heart failure, and heart attack modestly increased with the increase of weekly servings of fried food.[14] The study concluded that fried food consumption may increase the risk of cardiovascular disease and presents a linear dose-response relation.[14] The researchers theorized the main reasons behind these associations are the high trans fat and calorie content of fried foods and their pro-inflammatory nature.[14] It was also noted that eating hyperpalatable crisp-fried foods may entice people to engage in routine overeating.[14]
A 2023 meta-analysis found that fried food consumption is linked to a 52% increase in the risk of stomach cancer.[15] Fried food intake is also associated with prehypertension,[16] hypertension[17][18][16][19] and obesity.[19][20]
Effect of oil
Due to oil absorption during frying, the nutritional profile of the oil used becomes part of the final product; up to 75% of calories can be from fat in fried foods.[9] 15% of battered chicken or fish’s final weight is absorbed frying oil, compared to 20% when breaded. Doughnuts’ final weight is between 15–20% frying oil, and this figure increases to up to 35–40% for potato chips.[1]
Oil reuse reduces the nutritional value of foods, increases saturated and trans fats while reducing monounsaturated and polyunsaturated fats, and may introduce carcinogenic compounds such as aldehydes.[10]
Seed oils
Seed oils are used in frying due to their neutral flavour, low cost, and high smoke point when compared to other plant oils like olive, coconut, and palm oil, as well as animal fats like tallow.[21][1] Seed oils comprise mostly unsaturated fats, meaning they are better for heart health than saturated fats like butter and tallow, which increase cholesterol levels.[21][22] A 2022 WHO review and meta-analysis of 170 studies found that polyunsaturated fat consumption reduced overall mortality, but that higher quality evidence was needed.[23][24]
Seed oils have been the subject of criticism on social media, including by U.S. Secretary of Health and Human Services Robert F. Kennedy Jr., who said that consumers of seed oils are being "unknowingly poisoned".[22][21] RFK Jr. has also supported the conspiracy theories that vaccines cause autism and Wi-Fi causes cancer.[25][26] Critics on social media have called the most popular seed oils, including rapeseed and sunflower oil, "the hateful eight".[23][21]
Olive oil
Olive oil is stable at high temperatures because of its high antioxidant content, which makes it less likely to produce carcinogenic aldehydes during frying and improves the nutritional content of fried foods.[10]
Images
Guastedde a fried Sicilian dessert, in a shop window
See also
Notes
- Chemically, oils and fats are the same, differing only in melting point: oils are liquid at room temperature and fats are solid.[1]
