Frying
The art and science of cooking food in hot oil or fat.
Frying is the cooking of food in oil or fat, a dehydration process involving the transfer of both mass and heat. Unlike sautéing, where food is tossed in the pan, pan-fried items are typically turned over once or twice with tongs or a spatula to ensure even cooking. A vast array of foods can be prepared this way. During frying, several chemical changes occur: proteins denature, starches gelatinize, the surface browns, water rapidly evaporates, and oil is absorbed.
The practice of frying is ancient. Evidence suggests it first appeared in Ancient Egyptian cuisine during the Old Kingdom, around 2500 BC. In India, there is evidence of frying dating to approximately 1500 BC, using ghee to fry appam. In China, the *Book of Rites* records a Zhou dynasty recipe for fried rice using fat from a wolf’s breast. Stir frying is hypothesized to have emerged in field kitchens of the late Han dynasty, though it escaped literary record due to its informal nature. The biblical Book of Leviticus distinguishes between baked bread and bread fried in a pan with oil. In Europe, frying pans appear in Norwegian grave goods from the seventh century. Literary references to frying appear in the *Wife of Bath's Tale* (14th century) and *Don Quixote* (17th century), which mentions fried eggs.
When food contacts oil heated to a high temperature, heat and mass transfer begin. The food’s water content reaches boiling point and vaporizes, creating pores in cell walls that allow oil absorption. Greater heat exposure on the surface causes faster water vaporization there, forming a crisp crust that protects the interior from further oil uptake. The crust browns due to melanoidin formation from caramelization and the Maillard reaction. Starch gelatinization softens the food’s interior, while the surface, with less water, remains crisp. Frying is complete when all water content has vaporized. As the fried food cools below 100°C, internal water vapor condenses, dropping pressure and drawing oil into the food via a vacuum effect.
- common_oils
- Palm oil, rapeseed oil, sunflower oil, olive oil, peanut oil
- key_chemical_changes
- Protein denaturation, starch gelatinization, Maillard reaction, caramelization
- health_risk_increase_all_cause_mortality
- 3% (highest vs. lowest consumption)
- health_risk_increase_stomach_cancer
- 52%
Lore & Background
Frying is believed to have first appeared in Ancient Egyptian cuisine during the Old Kingdom, around 2500 BC. There is evidence of frying dating to c. 1500 BC in India, when ghee was used to fry appam. In China, the Book of Rites describes a Zhou dynasty-era recipe for fried rice and fat from a wolf's breast. In Leviticus, a distinction is made between baked bread and bread fried in a pan with oil. In Europe, frying pans begin appearing in Norwegian grave goods in the seventh century. 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.
Reader's Guide
When in contact with oil heated to high temperature, food undergoes heat and mass transfer. The food's water content reaches boiling point and begins to vaporise, creating pores in its cell walls which enable it to absorb oil. 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. 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. Frying is complete when all water content in the food vaporises. When a fried food reduces in temperature below 100°C, water vapour inside condenses and internal pressure drops, causing oil absorption into the food via a vacuum effect. Techniques include deep frying, sautéing, shallow frying (also known as pan frying), and stir frying. Stir frying is a Chinese, high-heat technique using a wok in which ingredients are constantly stirred for even cooking. The base of the wok is placed directly in the fire and its concave shape allows the flames to envelop the bowl; the base of the wok can reach 400°C. Frying is finished in two to three minutes.
Did You Know?
- 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 card
- A 2023 meta-analysis found that fried food consumption is linked to a 52% increase in the risk of stomach cancer.
- Up to 75% of calories can be from fat in fried foods due to oil absorption.
- Toxic compounds such as aldehydes (e.g. formaldehyde) are produced during frying and evaporate with steam, which can irritate lung tissue if inhaled.
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