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Fried plantain

Frying is the cooking of food in oil or another fat.[a][1] Similar to sautéing, pan-fried foods are generally turned over once or twice during cooking to make sure that the food is evenly cooked, using tongs or a spatula, whilst sautéed foods are cooked by "tossing in the pan".[2] A large variety of foods may be fried.

History

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A painting by the Russian artist A. I. Morozov showing frying in the open air

Frying is believed to have first appeared in the Ancient Egyptian kitchen, during the Old Kingdom, around 2500 BC.[3] Around the Middle Ages, fried food became a common delicacy[clarification needed] for wealthy people, with fried meats and vegetables becoming popular dishes.[4]

It is believed that frying was created, and used, as a way to preserve food.[5]

Variations

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Unlike water, fats can reach temperatures much higher than 100 °C (212 °F) before boiling. This paired with their heat absorption properties, neutral or desired taste, and non-toxicity, makes them uniquely valuable in cooking, especially frying. As a result, they are used in a wide variety of cuisines.

Through frying, one can sear or even carbonize the surface of foods while caramelizing sugars. The food is cooked much more quickly and has a characteristic crispness and texture. Depending on the food, the fat will penetrate it to varying degrees, contributing richness, lubricity, its own flavour, and calories.

Frying techniques vary in the amount of fat required, the cooking time, the type of cooking vessel required, and the manipulation of the food. Sautéing, stir-frying, pan frying, shallow frying, and deep frying are all standard frying techniques.

Pan-frying, sautéing, and stir-frying involve cooking foods in a thin layer of fat on a hot surface, such as a frying pan, griddle, wok, or sautee. Stir frying involves frying quickly at very high temperatures, requiring that the food be stirred continuously to prevent it from adhering to the cooking surface and burning.

Shallow frying is a type of pan frying using only enough fat to immerse approximately one-third to one-half of each piece of food; fat used in this technique is typically only used once. Deep-frying, on the other hand, involves totally immersing the food in hot oil, which is normally topped up and used several times before being disposed of. Deep-frying is typically a much more involved process and may require specialized oils for optimal results.

Deep frying is now the basis of a very large and expanding worldwide industry. Fried products have consumer appeal in all age groups and in virtually all cultures, and the process is quick, can easily be made continuous for mass production, and the food emerges sterile and dry, with a relatively long shelf life. The end products can then be easily packaged for storage and distribution. Some include potato chips, French fries, nuts, doughnuts, and instant noodles.

Health

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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.[6] 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.[6] The risk of stroke, heart failure, and heart attack modestly increased with the increase of weekly servings of fried food.[6] The study concluded that fried food consumption may increase the risk of cardiovascular disease and presents a linear dose-response relation.[6] 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.[6] It was also noted that eating hyperpalatable crisp-fried foods may entice people to engage in routine overeating.[6]

A 2023 meta-analysis found that fried food consumption is linked to a 52% increase in the risk of stomach cancer.[7] Fried food intake is also associated with prehypertension,[8] hypertension[9][10][8][11] and obesity.[11][12]

See also

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Notes

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References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Frying

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from Grokipedia
Frying is a dry-heat cooking method that involves immersing or contacting food with hot oil or fat, typically at temperatures between 325°F and 450°F (163°C and 232°C) depending on the technique, to rapidly transfer heat and achieve a crispy exterior while retaining moisture inside.[1] This process, which dates back to ancient culinary practices such as Roman fritters described by Cato the Elder in the 2nd century BC and Chinese stir-frying that developed as a cooking technique during the Ming dynasty (1368–1644 AD) with earlier roots in grain drying during the Han dynasty (206 BC–220 AD), relies on simultaneous heat and mass transfer, where oil serves as both the cooking medium and a partial absorbent during preparation.[2][3] Common types of frying include sautéing, which uses a small amount of fat over high heat with frequent tossing for quick cooking of tender meats or vegetables like peppers and zucchini; pan-frying, employing a moderate amount of oil in a shallow pan for items such as chicken breasts or pork loin; stir-frying, involving constant stirring over high heat for thin strips of vegetables or meat; and deep-frying, where food is fully submerged in hot oil for products like French fries, fried chicken, or fish fillets.[4][5] These variations are widely used in global cuisines, from Asian stir-fries to Western deep-fried snacks, but all require careful temperature control to prevent oil degradation or food safety risks.[6] Frying enhances flavor through Maillard reactions and oil absorption, which can range from 8% to 25% of the food's weight, though excessive intake raises health concerns related to fat content and acrylamide formation at high temperatures.[1][7] Safety guidelines emphasize using stable oils with high smoke points, maintaining temperatures below 375°F to minimize oxidation where applicable, and ensuring foods reach a safe internal temperature, such as 165°F for poultry.[8] Modern innovations like air-frying reduce oil use by circulating hot air, offering a healthier alternative while mimicking traditional results.[9]

Fundamentals

Definition and Principles

Frying is a cooking method that involves immersing or partially submerging food in hot oil or fat, typically at temperatures between 163°C and 190°C (325°F and 375°F), to rapidly cook the exterior while developing a browned, crispy texture through dehydration and chemical reactions on the surface.[10][11] This process, known as a dry-heat technique, relies on the oil as the primary medium for heat delivery, distinguishing it from wet methods like boiling, which use water, or air-based methods like baking, where fat is absent or minimal.[10][12] The core principles of frying center on the efficient heat transfer properties of oil, which transfers heat more efficiently than air via convection and allows for higher cooking temperatures than water without boiling, enabling quick cooking that seals the food's surface and evaporates internal moisture as steam.[10][1] As the food contacts the hot oil, surface water rapidly vaporizes at around 100°C (212°F), creating bubbles that push oil away from deeper penetration while forming a dehydrated crust that traps remaining moisture inside, preserving tenderness in the interior.[10][12] This simultaneous heat and mass transfer—where heat moves into the food and water escapes—results in the characteristic crispiness and flavor enhancement, with oil absorption typically limited to 8–25% of the final product weight.[11][1] Optimal frying occurs within temperature ranges of 160–190°C (320–374°F) for most foods, allowing for efficient cooking without excessive oil degradation or uneven results; immersion levels vary but must ensure sufficient contact to promote uniform heat distribution.[11][12] Below this range, cooking slows and oil uptake increases, while exceeding it risks burning the surface before the interior cooks through.[1] These principles underscore frying's efficiency in achieving desirable sensory qualities, such as golden browning via surface reactions, while minimizing cooking time compared to other heat mediums.[10][12]

Heat Transfer in Frying

In frying, heat is primarily transferred from the hot oil to the food surface via convection, driven by the temperature difference and the circulation of the oil around the food, while conduction subsequently moves heat from the surface through the interior of the food along temperature gradients. Radiation contributes minimally to the overall heat transfer process, as the oil and food materials are largely opaque to infrared wavelengths at typical frying temperatures, limiting radiative exchange between the food and surrounding oil.[13][14] The rapid initial heating of the food surface in frying results from oil's superior heat transfer properties compared to air; specifically, oil's volumetric heat capacity—approximately 1,800 times greater than that of air due to its higher density and specific heat—allows it to deliver thermal energy more efficiently to the food, enabling quicker temperature rise at the interface than in dry-heat methods like baking. This enhanced convection in the liquid medium yields heat transfer coefficients typically ranging from 200 to 800 W/m²·K during frying, far exceeding those in air (around 10-100 W/m²·K), which promotes uniform and swift surface cooking.[15][16] As frying progresses, surface moisture in the food rapidly vaporizes upon contact with the hot oil, forming a steam layer or "blanket" that insulates the food and reduces the convective heat transfer rate by creating a low-conductivity vapor barrier between the oil and the developing crust. This phenomenon initially accelerates water loss through bubbling but subsequently slows internal heat penetration, extending the time required for core cooking and contributing to the characteristic crispy exterior with a moist interior in properly fried foods. Several factors modulate the heat transfer rate in frying. Higher oil temperatures generally enhance convective transfer by increasing the temperature gradient and reducing oil viscosity, though excessive heat can lead to crust formation that further impedes conduction; for instance, frying at 180°C versus 160°C can double the initial heat flux in potato strips. Food geometry plays a key role in conduction, with smaller or thinner pieces allowing faster internal equilibration due to shorter diffusion paths, while larger items require longer times to reach uniform temperatures. Agitation of the oil, whether through natural bubbling or mechanical stirring, boosts convection by promoting turbulent flow and renewing the boundary layer at the food surface, potentially increasing the heat transfer coefficient by 20-50% compared to static conditions.[17][18][19]

Techniques

Shallow and Pan Frying

Shallow frying employs a moderate amount of oil, typically 1/4 to 3/4 inch (0.6 to 1.9 cm) deep, allowing food to be partially submerged while maintaining contact with the pan's base for even browning.[20] In contrast, pan frying uses a thin film of oil, just enough to coat the pan's surface and lubricate the food, emphasizing direct heat conduction from the pan.[21] Both methods rely on flipping or turning the food midway through cooking to achieve uniform crispiness on all sides, often with a spatula to preserve shape and texture.[22] These techniques suit a variety of foods, including thin cuts of meat like chicken cutlets or pork chops, fish fillets, and vegetables such as potatoes for hash browns or eggplant slices.[23] Ideal oil temperatures range from 160–180°C (320–356°F), ensuring rapid heat transfer without excessive smoking, though adjustments may be needed based on food thickness.[23] At these temperatures, the surface develops a golden crust via the Maillard reaction while the interior cooks through steaming from the oil.[21] The process begins by preheating the oil in a heavy-bottomed pan over medium-high heat until it shimmers or reaches the target temperature, tested by a wooden spoon handle bubbling in the oil.[21] Food, patted dry and at room temperature, is then added without crowding to avoid temperature drops, cooking undisturbed until the edges crisp and color shifts to golden brown.[24] Doneness is monitored by texture—firm yet juicy for meats—and visual cues like even browning, with flipping once to complete cooking, followed by draining on paper towels.[22] Advantages include significantly reduced oil consumption compared to full submersion methods, promoting healthier outcomes with less fat absorption.[24] In pan frying particularly, the minimal oil allows flavorful browned residues, or fond, to develop on the pan base, which can be deglazed for sauces enhancing the dish.[21] This control over heat and oil also facilitates household applications, yielding crispy exteriors and moist interiors with straightforward equipment.[23]

Deep Frying

Deep frying involves completely submerging food items in a large volume of hot oil, typically at temperatures between 175°C and 190°C, to achieve even cooking and a crispy exterior through rapid heat transfer via convection.[1] The oil depth must be sufficient—generally at least 5 cm or more—to ensure full immersion, allowing the food to cook uniformly without surface exposure to air.[25] In both industrial and home settings, wire mesh baskets are commonly used to hold and lower batches of food into the oil, facilitating easy retrieval and promoting efficient batch processing while permitting oil circulation around the items.[26] This technique is widely applied to foods like French fries and tempura, where the high heat quickly seals the surface, creating a crisp texture.[27] Batters or coatings, such as those made from flour, egg, and cold water in tempura preparations, play a crucial role by forming a protective barrier that minimizes oil absorption into the food while enhancing crispiness and flavor retention.[28] These coatings prevent excessive moisture loss and oil penetration, resulting in lower fat content in the final product compared to uncoated items fried under similar conditions.[29] Proper oil maintenance is essential for safety and quality, involving regular filtering to remove food debris and particles that can accelerate oil degradation.[30] Avoiding overcrowding the fryer is critical, as adding too much food at once lowers the oil temperature, leading to uneven cooking and increased oil uptake by the food.[31] Filtered oil can be reused multiple times if stored properly, extending its lifespan and reducing waste. Deep frying offers high energy efficiency in commercial operations due to its ability to process large batches quickly, with capacities yielding 120 to 160 pounds of fried food per hour in standard 80-pound oil fryers.[32] However, it requires greater oil consumption than other methods because of the need for substantial volumes to maintain submersion and temperature stability, contributing to higher operational costs over time.[33]

Stir and Sauté Frying

Stir frying and sautéing are high-heat cooking methods that use minimal oil to quickly cook food through constant agitation, promoting even browning and texture retention while preserving nutrients. Sautéing typically employs a wide, shallow sauté pan or skillet, where ingredients are tossed or flipped to ensure uniform exposure to heat, often at medium-high temperatures for more controlled cooking. In contrast, stir frying utilizes a wok with its rounded bottom and high sides, allowing for dramatic flipping and sliding of ingredients to leverage varying heat zones, which enables faster cooking and distinct flavor development through rapid searing. These techniques differ primarily in vessel design and motion intensity, with stir frying emphasizing relentless stirring to mimic professional wok hei, or "breath of the wok," a subtle smoky essence from intense heat.[34][35] Optimal temperatures for both methods range from 190–220°C (375–425°F), ensuring the oil shimmers without smoking excessively, which allows proteins and vegetables to sear quickly while minimizing oil absorption. A key technique in stir frying, particularly for Chinese preparations, is velveting, where thin slices of meat or seafood are marinated in a mixture of cornstarch, egg white, and seasonings before brief blanching or direct stir frying; this creates a protective coating that seals in moisture, resulting in tender, silky textures despite high heat. Velveting is especially effective for tougher cuts, transforming them into succulent pieces that integrate seamlessly with other ingredients.[34][36] These methods pair well with ingredients that cook rapidly, such as thinly sliced meats like beef, pork, or chicken, and bite-sized vegetables including broccoli, bell peppers, snow peas, and carrots, which maintain crispness when exposed briefly to heat. The standard cooking sequence begins with heating oil and infusing it with aromatics—such as garlic, ginger, or scallions—to build a flavorful base, followed by adding proteins to sear briefly, then incorporating denser vegetables before quicker-cooking greens; this order prevents overcooking delicate items and allows flavors to layer progressively. Sauces, often thickened with cornstarch slurry, are added last to glaze without diluting earlier sears.[34][37]

Equipment

Cookware and Vessels

Cast iron cookware is prized for its exceptional heat retention, making it ideal for pan frying where consistent temperatures are essential to achieve even browning without frequent adjustments to the heat source.[38] This material's high volumetric heat capacity allows it to maintain heat effectively once preheated, supporting techniques that require sustained high temperatures.[39] Stainless steel pans offer superior durability, resisting warping and corrosion even under repeated high-heat use, which ensures longevity in demanding frying applications.[40] Their robust construction, often featuring multi-ply designs with aluminum cores, provides reliable performance over years of service.[41] Non-stick coatings, typically applied to aluminum or hard-anodized bases, facilitate low-oil sauté frying by minimizing adhesion and allowing food release with little to no added fat.[42] These surfaces promote healthier cooking options while simplifying cleanup after quick, high-heat operations.[43] Skillets, with their shallow, flat-bottomed design and gently sloped sides, are well-suited for shallow frying, enabling efficient oil use and easy maneuvering of foods like cuts of meat or vegetables.[44] Dutch ovens, characterized by their deep, wide cavities and tight-fitting lids, serve as effective vessels for deep frying, containing large volumes of oil while distributing heat evenly to prevent hot spots.[45] Their cast iron construction enhances temperature stability during prolonged immersion frying.[46] Woks, featuring curved, sloping sides that rise steeply from a central point of contact with the heat, are optimized for stir frying, as the shape facilitates rapid tossing and even distribution of ingredients across varying heat zones.[34] When selecting frying cookware, depth plays a key role in accommodating oil volume; shallow pans around 1.5 to 2 inches suit versatile shallow methods, while deeper vessels exceeding 3 inches support deep frying by submerging items fully.[47] Surface area, measured by the pan's diameter at the top rim, determines batch capacity, with wider bases (typically 10 to 12 inches) allowing larger portions without overcrowding, which maintains oil temperature and crisp results.[48] Proper maintenance extends the life of frying vessels; cast iron requires seasoning, a process involving applying a thin layer of oil and baking at moderate heat to create a protective, non-stick polymerized surface that builds with use.[49] For non-stick pans, avoiding overheating—such as preheating empty on high—prevents degradation of the coating, preserving its low-friction properties and safety.[50]

Monitoring and Safety Tools

Monitoring oil temperature during frying is essential to achieve optimal heat transfer, prevent oil degradation, and ensure food safety by avoiding under- or overcooking.[51] Thermometers designed for frying include candy or deep-fry models, which clip onto the pot edge and measure oil temperatures from 100°F to 400°F, allowing precise control to maintain ideal frying ranges of 350°F to 375°F.[52] These are preferred over general kitchen thermometers due to their high-temperature tolerance and visibility above the oil surface. Infrared thermometers provide non-contact measurement of oil surfaces, offering quick readings up to 700°F and reducing the risk of burns, though they measure only surface temperature and may require calibration for accuracy in deep pots.[53][54] Handling tools facilitate safe manipulation of food in hot oil. Slotted spoons enable draining excess oil while retrieving items, minimizing splatter and burns by allowing liquids to pass through perforations.[55] Tongs with heat-resistant, non-slip grips securely grasp and flip foods, keeping hands at a safe distance from the hot surface.[56] Splatter screens, typically fine-mesh metal guards that fit over pans, contain oil pops and sprays during frying, protecting skin and countertops from burns and messes.[57] Safety gear mitigates injury risks from heat and fire. Fireproof aprons, often made from flame-resistant fabrics, shield clothing and skin from splatters and radiant heat in commercial or home kitchens.[58] Class B fire extinguishers, suitable for grease and oil fires, discharge dry chemical agents to smother flames without spreading the blaze, and should be kept accessible but used only as a last resort after attempting to cover the pan.[59] Digital aids enhance precision in timing and internal temperature checks. Digital timers track cooking durations to prevent over-frying, integrating with alarms for consistent results. Probes, such as thermocouple types, insert into food to monitor internal temperatures in real-time via digital displays, ensuring safe minimums like 165°F for poultry without relying on visual cues.[51][52]

Science

Chemical Reactions

During frying, the Maillard reaction occurs between reducing sugars and amino acids in food components, leading to the formation of melanoidins that impart characteristic browning, complex flavors, and umami taste to fried foods. This non-enzymatic browning reaction is optimal at temperatures between 140°C and 165°C, where the rate of formation of flavor volatiles and color compounds accelerates significantly without excessive degradation.[60][61] In fried items like battered meats or potato products, the reaction enhances sensory appeal but can also generate acrylamide from asparagine and sugars under prolonged high-heat exposure.[60] Hydrolysis and oxidation are primary degradation pathways in frying oils, triggered by moisture from food and atmospheric oxygen at elevated temperatures. Hydrolysis breaks down triglycerides into free fatty acids, mono- and diacylglycerols, increasing oil acidity and contributing to rancid off-flavors if the process extends beyond optimal frying durations.[62] Concurrently, oxidation of unsaturated fatty acids forms hydroperoxides and secondary products like aldehydes, which degrade oil stability and impart undesirable tastes, particularly in repeatedly used oils.[62] These reactions are exacerbated above 180°C, leading to polymerized compounds that alter viscosity and foam characteristics.[63] Caramelization, a thermal decomposition of sugars independent of proteins, contributes to surface browning and sweet, nutty flavors in fried foods containing carbohydrates, such as vegetable coatings or starchy items. This reaction predominates at temperatures exceeding 150°C, breaking down sugars like sucrose into volatile aromatics and brown pigments, complementing Maillard effects in products like french fries or caramelized onion fritters.[12] Unlike the Maillard reaction, it does not require amino acids but can overlap in high-sugar foods during frying.[60] Glycation during frying involves the initial binding of reducing sugars to free amino groups on proteins or lipids, progressing to the formation of advanced glycation end-products (AGEs) through oxidative steps in the Maillard pathway. In fried foods, such as fish cakes or shrimp, AGEs like Nε-carboxymethyllysine accumulate rapidly due to high temperatures (around 177°C) and low moisture, enhancing color but potentially altering texture via protein cross-linking.[64] Frying methods yield higher AGE levels compared to moist cooking, with batter-coated products showing elevated formation from lipid oxidation interactions.[65]

Oil Properties and Selection

The selection of oils for frying depends on their physical and chemical properties, which ensure efficient heat transfer, minimize degradation, and maintain food quality during high-temperature exposure. These properties include the smoke point, fatty acid profile, viscosity, and density, each contributing to the oil's suitability for shallow or deep frying applications. Proper selection prevents off-flavors, excessive foaming, and rapid breakdown, allowing for optimal cooking performance. The smoke point represents the temperature at which an oil visibly smokes and begins to decompose, releasing potentially harmful compounds and imparting bitter tastes to food. Refined oils generally exhibit higher smoke points due to the removal of impurities and free fatty acids during processing, making them ideal for frying at temperatures typically ranging from 160–190°C. For instance, refined canola oil has a smoke point of 204°C, enabling sustained high-heat use without breakdown. In contrast, unrefined fats like butter possess lower smoke points, around 150°C, limiting their application to lower-temperature sautéing to avoid rapid decomposition.[66][67] Fatty acid composition significantly influences an oil's oxidative stability and flavor development during frying. Oils high in saturated fatty acids, such as palm oil with approximately 49% saturated fats (primarily palmitic and stearic acids), demonstrate superior thermal stability, resisting polymerization and rancidity over multiple uses. This composition minimizes the formation of harmful byproducts at frying temperatures. Conversely, oils rich in polyunsaturated fatty acids, like soybean oil, enhance flavor through volatile compound release but are more susceptible to oxidation and rancidity, leading to quicker degradation and off-odors upon repeated heating. Balancing these profiles—often through blending—optimizes both stability and sensory qualities.[68][69] Viscosity, the oil's resistance to flow, and density, its mass per unit volume, directly impact heat transfer efficiency and food behavior in the fryer. Lower viscosity facilitates better convective heat transfer from the oil to the food surface, promoting uniform cooking, while higher viscosity—often increasing with repeated frying due to polymerization—can slow this process and lead to uneven heating. Density affects food buoyancy, with lower density oils allowing fried items to float more readily and reduce oil uptake. These properties typically decrease with rising temperature: viscosity exponentially and density linearly, influencing overall frying dynamics without significantly altering chemical reactions in the oil medium.[17][70] To extend usability, frying oils must be monitored for degradation indicators, with reuse limited by the accumulation of total polar compounds (TPCs), which form from hydrolysis, oxidation, and polymerization. Standards recommend discarding oil when TPCs exceed 25–27% by weight, as higher levels compromise safety and quality, evidenced by increased viscosity and foaming, as well as practical signs such as dark murky color, excessive foaming, rancid fishy or sour smell, smoking at normal frying temperatures, and thick or gummy texture. Discard immediately upon observing these signs to avoid off-flavors and harmful compounds. This threshold, adopted in regulations like those from the Food Safety and Standards Authority of India, ensures oils remain viable for 8–12 frying cycles depending on conditions, prioritizing filtration and storage to delay TPC buildup.[71][72][73][74]

History

Ancient Origins

The practice of frying emerged in ancient civilizations where access to oils and fats allowed for cooking foods submerged or coated in hot fat, marking a significant advancement over roasting or boiling. The earliest documented evidence comes from ancient Egypt around 2500 BCE, where frying was used to prepare pastries and other dishes, as indicated by archaeological and textual records of oil-based cooking.[75] By the 18th Dynasty (c. 1550–1292 BCE), tomb paintings, such as those in the tomb of Vizier Rekhmire at Thebes (c. 1450 BCE), depict scenes of food preparation involving hot oil, including the frying of dough-based items like cakes made from tiger nuts or grains.[76] Egyptians employed sesame oil, derived from locally cultivated plants, for frying, alongside other fats like animal tallow and emerging olive oil imports, reflecting a diet that integrated frying for preservation and flavor enhancement.[77] In Mesopotamia, contemporaneous with early Egyptian practices, cooking technologies supported oil use, though direct evidence of frying is limited. Clay tablets from the Yale Babylonian Collection, dating to approximately 1750 BCE, preserve the oldest known culinary recipes, primarily for broths and stews.[78] These recipes highlight the role of sesame and other seed oils in Mesopotamian cuisine. The technique spread eastward to ancient China, where stir-frying developed during the Han dynasty (206 BCE–220 CE), using small amounts of oil in woks over high heat for quick cooking of vegetables and meats, as described in early texts like the Shijing and archaeological findings of bronze vessels.[79] It also spread westward through trade networks, reaching ancient Greece by the 5th century BCE, where olive oil—abundant due to Mediterranean cultivation—became central to frying. Greek writers like Aristophanes referenced fried dough pancakes (tiganites), prepared in shallow olive oil over hearths, as everyday fare offered to gods and consumed during festivals.[80] Romans further popularized frying via imperial expansion, incorporating Eastern oils and adopting Greek methods; the De Re Coquinaria attributed to Apicius (compiled c. 1st century CE) includes explicit fried recipes, such as aliter isicia omentata (fried forcemeat patties) and honey-dipped fritters (globuli), cooked in olive oil or lard for elite banquets. Early frying tools evolved from simple clay vessels used in Egyptian and Mesopotamian hearths for shallow oil cooking to more durable metal implements. In the Indus Valley Civilization (c. 2600–1900 BCE), copper vessels resembling frying pans, excavated at Mohenjo-Daro, indicate specialized cookware for oil-based methods, possibly for flatbreads or spiced preparations, showcasing parallel metallurgical innovation in South Asia.[81] This progression from earthenware pots to bronze and copper skillets facilitated efficient heat distribution and oil containment across these interconnected ancient societies.

Modern Developments

The industrialization of frying in the 19th century marked a shift toward commercial production and specialized equipment in Europe, particularly with the rise of deep-frying for street foods and snacks. In Britain, the combination of deep-fried fish and potatoes into fish and chips emerged around 1860, pioneered by Joseph Malin in London, who sold the dish from a street cart using basic metal baskets and vats for immersion frying.[82] This innovation reflected growing urban demand for quick, affordable meals, with frying vessels evolving from open pots to more efficient wire-mesh baskets suspended in hot oil to prevent sticking.[83] Across the Atlantic, the invention of the potato chip in 1853 by George Crum, a chef at Moon's Lake House in Saratoga Springs, New York, further popularized shallow frying techniques for snacks; Crum reportedly created thin-sliced, fried potatoes in response to a customer's complaint about thick-cut ones.[84] The 20th century brought technological advancements that made frying safer, more consistent, and accessible for both commercial and home use. Electric deep fryers appeared in the early 1920s, with early models like those from hotel equipment manufacturers using thermostatically controlled heating elements to maintain stable oil temperatures, reducing fire risks associated with open-flame methods.[85] By the 1940s, fast-food chains standardized frying processes; McDonald's, founded by the McDonald brothers in San Bernardino, California, in 1940, introduced French fries to its menu in 1949, using a double-fry method in beef tallow for crispiness and uniformity, which became a cornerstone of its global menu.[86] This era also saw pressure fryers, such as the Broaster model developed in 1954, which combined frying with steam under pressure to cook chicken faster while retaining moisture, influencing the expansion of fried poultry in restaurants.[87] Post-World War II globalization fused frying traditions across cultures, particularly in Asia, where Western fast-food concepts adapted local tastes. Kentucky Fried Chicken (KFC) entered Japan in 1970 with a test outlet at the Osaka World's Fair, followed by its first permanent store in Nagoya; the chain's pressure-fried chicken quickly gained popularity, eventually becoming a Christmas tradition by the mid-1970s due to marketing campaigns positioning it as a festive alternative to turkey.[88] Since the 2010s, vegan frying has emerged as a significant trend, driven by the rise of plant-based diets and the development of oil-free or low-oil alternatives; for instance, vegan adaptations of fried foods using chickpea flour batters or coconut oil have proliferated in global cuisine, aligning with a broader surge in plant-based diets, with vegan identification in the US increasing approximately 600% from 2014 to 2017.[89] Recent innovations have focused on health-conscious modifications to traditional frying, exemplified by the air fryer, which simulates deep-frying effects using rapid hot air circulation to minimize oil. Invented by Dutch engineer Fred van der Weij in 2006 and commercially launched by Philips in 2010 as the "Airfryer," this appliance reduces fat content by up to 80% compared to immersion methods while achieving similar textures, appealing to consumers seeking lower-calorie options.[90] By the mid-2010s, air fryers had expanded into multi-function models, influencing home cooking trends toward versatile, oil-sparing preparations of items like French fries and chicken wings.[91]

Health and Safety

Nutritional Effects

Frying significantly alters the nutritional profile of foods primarily through fat absorption, which can increase the weight of fried products by 8 to 25 percent due to oil uptake, with deep frying resulting in the highest absorption rates compared to shallow or stir-frying methods.[1] This oil incorporation not only elevates fat content but also contributes to changes in other nutrients, as the process involves high temperatures that promote both retention and loss of vitamins depending on their solubility. Water-soluble vitamins, such as vitamin C and B vitamins (e.g., thiamine, riboflavin, and niacin), are particularly vulnerable during frying, with losses of approximately 30 percent for thiamine and 42-44 percent for riboflavin in fried liver, often due to leaching into the frying oil or thermal degradation.[27] In contrast, fat-soluble vitamins like A and E exhibit variable retention; vitamin A may decrease by about 24 percent in fried vegetables, while vitamin E can increase in fried items such as chicken nuggets (from 4.6 to 4.9 mg per 100 g) owing to transfer from the oil.[27] The caloric density of foods rises notably after frying due to oil absorption and the formation of Maillard reaction products, which enhance flavor but accompany the added fats; for instance, breaded and fried chicken breast contains approximately 260–270 kcal per 100 g, compared to 165 kcal per 100 g for grilled chicken breast, yielding a difference of about 100–200 kcal per 100 g primarily from the oil.[92][93] Despite these losses, frying can offer nutritional benefits in specific cases, such as enhanced bioavailability of lycopene in tomatoes; cooking tomatoes in oil, as in frying, increases lycopene absorption compared to raw consumption, with processed forms like tomato paste providing up to threefold higher plasma lycopene levels than fresh tomatoes when consumed with fat.[94][95]

Risks and Precautions

Frying poses significant fire risks due to the high temperatures involved, with cooking oils reaching auto-ignition points typically between 400°C and 450°C for common vegetable oils like canola, vegetable, and olive oil, potentially leading to spontaneous combustion if overheated.[96] To mitigate these dangers, operators must never leave hot oil unattended on the stove, as unattended heating is a leading cause of kitchen fires.[97] If a grease fire ignites, immediately turn off the heat source and smother the flames with a tight-fitting metal lid to cut off oxygen supply; water should never be used, as it can cause explosive splattering and intensify the fire.[98] Keeping a Class K fire extinguisher nearby provides an additional safeguard for larger incidents.[99] Burns from hot oil splatters represent another immediate physical hazard, often resulting from moisture in food vaporizing rapidly upon contact with the oil.[100] The U.S. Department of Agriculture recommends drying food thoroughly before frying and avoiding addition of wet ingredients to prevent such splatters, while using a splatter screen over the pan can further contain eruptions.[100] Protective measures also include wearing long sleeves, aprons, and gloves to shield skin from incidental contact. Chemically, frying starchy foods such as potatoes at temperatures exceeding 120°C promotes the formation of acrylamide, a probable human carcinogen that arises from the Maillard reaction between sugars and amino acids. Regulatory bodies like the European Commission have set benchmark levels for acrylamide in foods, such as 750 µg/kg for potato fries (as of 2020), to encourage mitigation efforts.[101] Levels in french fries can surpass 1,000 µg/kg, with some samples reaching up to 2,000 µg/kg or more depending on frying conditions.[102] Mitigation strategies focus on lowering frying temperatures to below 175°C where possible, alongside techniques like blanching potatoes prior to frying to reduce precursor compounds.[103] Inhaling frying fumes exposes individuals to toxic emissions including polycyclic aromatic hydrocarbons (PAHs), aldehydes, and volatile organic compounds, which can induce oxidative stress, respiratory irritation, and elevated risks of lung cancer and cardiovascular disease with prolonged exposure.[104] Effective kitchen ventilation, such as operating a range hood that vents outdoors at 100 cubic feet per minute or higher, is crucial to dilute and exhaust these pollutants.[105] Additionally, used frying oil should be strained to remove food particles, cooled completely, and stored in a clean, airtight, light-proof container in a cool location or refrigerator to prevent rancidity and bacterial growth that could pose secondary hazards.[106] Reused frying oil that has gone bad should be discarded immediately, as indicated by signs such as a dark murky color, excessive foaming, a rancid fishy or sour smell, smoking at normal frying temperatures, or a thick or gummy texture; continuing to use such oil can impart off-flavors to food and lead to the formation of harmful compounds.[107][106][108]

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