Deep frying (also referred to as deep fat frying) is a

cooking Cooking, cookery, or culinary arts is the art, science and craft of using heat to prepare food for consumption. Cooking techniques and ingredients vary widely, from grilling food over an open fire to using electric stoves, to baking in vari ...

method in which food is submerged in hot fat, traditionally

lard Lard is a semi-solid white fat product obtained by rendering the fatty tissue of a pig.Lard
entry in the ...

but today most commonly oil, as opposed to the shallow oil used in conventional

frying Frying is the cooking of food in oil or another fat. Similar to sautéing, pan-fried foods are generally turned over once or twice during cooking to make sure that the food is well-made, using tongs or a spatula, while sautéed foods are coo ...

done in a

frying pan A frying pan, frypan, or skillet is a flat-bottomed pan used for frying, searing, and browning foods. It is typically in diameter with relatively low sides that flare outwards, a long handle, and no lid. Larger pans may have a small grab ha ...

. Normally, a deep fryer or chip pan is used for this; industrially, a pressure fryer or vacuum fryer may be used. Deep frying may also be performed using oil that is heated in a pot. Deep frying is classified as a hot-fat cooking method. Typically, deep frying foods cook quickly: all sides of the food are cooked simultaneously as oil has a high rate of heat conduction. The term "deep frying" and many modern deep-fried foods were not invented until the 19th century, but the practice has been around for millennia. Early records and cookbooks suggest that the practice began in certain European countries before other countries adopted the practice. Deep frying is popular worldwide, with deep-fried foods accounting for a large portion of global caloric consumption. Many foods are deep-fried and cultures surrounding deep frying have developed, most notably in the

Southern United States The Southern United States (sometimes Dixie, also referred to as the Southern States, the American South, the Southland, or simply the South) is a geographic and cultural region of the United States of America. It is between the Atlantic Ocean ...

and the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

, where many events and records are held relating to deep frying food and non-edible items.

History

The English expression ''deep-fried'' is attested from the early 20th century. Deep-fried dough known as Zalabiyeh was eaten as early as the late 2nd millennium BC in

Canaan Canaan (; Phoenician: 𐤊𐤍𐤏𐤍 – ; he, כְּנַעַן – , in pausa – ; grc-bib, Χανααν – ;The current scholarly edition of the Greek Old Testament spells the word without any accents, cf. Septuaginta : id est Vetus T ...

. Recipes for the dessert also exist in 10th and 13th century cook books by

Ibn Sayyar al-Warraq ( ar, أبو محمد المظفر بن نصر ابن سيار الوراق) was an Arab author from Baghdad. He was the compiler of a tenth-century cookbook, the ( ar, links=no, كتاب الطبيخ, ''The Book of Dishes''). This is the earlies ...

and

Muhammad bin Hasan al-Baghdadi Muḥammad bin al-Ḥasan bin Muḥammad bin al-Karīm al-Baghdadi, usually called al-Baghdadi (d. 1239 AD), was the compiler of an early Arabic cookbook of the Abbasid period, كتاب الطبيخ ''Kitab al-Ṭabīḫ'' (''The Book of Dishes'') ...

, respectively. Frying food in

olive oil Olive oil is a liquid fat obtained from olives (the fruit of ''Olea europaea''; family Oleaceae), a traditional tree crop of the Mediterranean Basin, produced by pressing whole olives and extracting the oil. It is commonly used in cooking: ...

is attested in

Classical Greece Classical Greece was a period of around 200 years (the 5th and 4th centuries BC) in Ancient Greece,The "Classical Age" is "the modern designation of the period from about 500 B.C. to the death of Alexander the Great in 323 B.C." (Thomas R. Martin ...

from about the 5th century BCE. The practice of deep frying spread to other parts of

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located enti ...

and

Arabia The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plate. ...

in the following centuries. Deep-fried foods such as funnel cakes arrived in northern Europe by the 13th century, and deep-fried fish recipes have been found in cookbooks in Spain and Portugal at around the same time.

Falafel Falafel (; ar, فلافل, ) is a deep-fried ball or patty-shaped fritter in Middle Eastern cuisine (especially in Levantine and Egyptian cuisines) made from ground chickpeas, broad beans, or both. Nowadays, falafel is often served in ...

arrived in the

Middle East The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolitical region commonly encompassing Arabia (including the Arabian Peninsula and Bahrain), Asia Minor (Asian part of Turkey except Hatay Province), East Thrace (Europ ...

from

Egypt Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Med ...

as early as the 14th century.

French fries French fries ( North American English), chips ( British English), finger chips (Indian English), french-fried potatoes, or simply fries, are '' batonnet'' or '' allumette''-cut deep-fried potatoes of disputed origin from Belgium and France ...

, invented in the late 18th century, became popular in the early 19th century western Europe. In 1860, Joseph Malin combined deep fried fish with chips (french fries) to open the first fish and chip shop in London. Modern deep frying in the United States began in the 19th century with the growing popularity of

cast iron Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impu ...

, particularly around the

American South The Southern United States (sometimes Dixie, also referred to as the Southern States, the American South, the Southland, or simply the South) is a geographic and cultural region of the United States of America. It is between the Atlantic Ocean ...

which led to the development of many modern deep-fried dishes.

Doughnut A doughnut or donut () is a type of food made from leavened fried dough. It is popular in many countries and is prepared in various forms as a sweet snack that can be homemade or purchased in bakeries, supermarkets, food stalls, and fran ...

s were invented in the mid-19th century, with foods such as

onion ring An onion ring, also called a French fried onion ring, is a form of appetizer or side dish in British and American cuisine. They generally consist of a cross-sectional "ring" of onion dipped in batter Batter or batters may refer to: Common ...

s, deep-fried turkey, and corn dogs all being invented in the early 20th century. In recent years, the growth of

fast food Fast food is a type of mass-produced food designed for commercial resale, with a strong priority placed on speed of service. It is a commercial term, limited to food sold in a restaurant or store with frozen, preheated or precooked ingredie ...

has expanded the reach of deep-fried foods, especially french fries.

Technique

Deep frying food is defined as a process where food is completely submerged in hot oil at temperatures typically between and , but deep frying oil can reach temperatures of over 400 °F (205 °C). One common method for preparing food for deep frying involves adding multiple layers of

batter Batter or batters may refer to: Common meanings * Batter (cooking), thin dough that can be easily poured into a pan * Batter (baseball), person whose turn it is to face the pitcher * Batter (cricket), a player who is currently batting * Batter ...

around the food, such as cornmeal, flour, or

tempura is a typical Japanese dish usually consisting of seafood, meat and vegetables that have been battered and deep fried. The dish was introduced by the Portuguese in Nagasaki through fritter-cooking techniques in the 16th century. The word '' ...

; breadcrumbs may also be used. While most foods need batter coatings for protection, it is not as necessary for cooked noodles and potatoes because their high starch content enables them to hold more moisture and resist shrinking. Meats may be cooked before deep frying to ensure that they are done inside while keeping juiciness. When performed properly, deep frying does not make food excessively greasy, because the moisture in the food repels the oil. The hot oil heats the water within the food, steaming it; oil cannot go against the direction of this powerful flow because (due to its high temperature) the water vapor pushes the bubbles toward the surface. As long as the oil is hot enough and the food is not immersed in the oil for too long, oil penetration will be confined to the outer surface. Foods deep-fried at proper temperatures typically absorb "no more than a couple of tablespoons per cups of oil" used. This oil absorption rate is around the same as occurs with shallow frying, such as in a pan. However, if the food is cooked in the oil for too long, much of the water will be lost and the oil will begin to penetrate the food. The correct frying temperature depends on the thickness and type of food, but in most cases it lies between . An informal test for a temperature close to this range involves adding a tiny amount of flour into the oil and watching to see if it sizzles without immediately burning. A second test involves adding one piece of food to deep fry and watching it sink somewhat and rise back up. Sinking without resurfacing indicates that the oil is too cold; not sinking at all indicates that the oil is too hot. It is recommended that deep fryers be cleaned often to prevent contamination. The process of cooking with oil can also contaminate nearby surfaces as oil may splatter on adjacent areas. Oil vapors can also condense on more distant surfaces such as walls and ceilings. Supplies such as dish detergent and baking soda can effectively clean affected surfaces.

Tools

Deep frying is done with a deep fryer, a pan such as a wok or chip pan, a Dutch oven, or a cast-iron pot. Additional tools include fry baskets, which are used to contain foods in a deep fryer and to strain foods when removed from the oil, and

cooking thermometer A thermometer is a device that measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a mercury-in-glass thermometer ...

s, used to gauge oil temperature. Tongs, slotted spoons, wooden spoons, and

sieve A sieve, fine mesh strainer, or sift, is a device for separation process, separating wanted elements from unwanted material or for controlling the particle size distribution of a sample, using a screen such as a warp and weft, woven mesh or n ...

s may be used to remove or separate foods from the hot oil. Japanese deep frying tools include long metal chopsticks; the '' agemono-nabe'' deep frying pot, which is heavy for retaining heat and deep for holding oil; the '' ami-shakushi'' net ladle used for scooping out batter debris; and the '' abura-kiri'' oil drying rack pan. File:Deep fryer.JPG, alt=A white plastic device shaped like a bucket, with controls on the front., A deep fryer with slotted spoon, for removing foods from the hot oil File:Tongs2.JPG, alt=Two pieces of metal joined at one end by a hinge, with the other end flat and ridged., Tongs File:Handmade wooden spoons.jpg, alt=Wooden spoons and other utensils for frying., Slotted and perforated wooden spoons File:Filters, അരിപ്പ.JPG, alt=Several wire meshes shaped like bowls, with metal handles., Various strainers, including a

spider Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species d ...

, left File:EmpanadaFry.jpg, alt=A metal bowl with many small holes., A strainer used in the preparation of

empanada An empanada is a type of baked or fried turnover consisting of pastry and filling, common in Spanish, other Southern European, Latin American, and Iberian-influenced cultures around the world. The name comes from the Spanish (to bread, i.e. ...

s File:Ami shakushi.Scoop.jpg, alt=A wire mesh on a long handle., An ami shakushi is a Japanese ladle or scoop that may be used to remove small drops of batter during the frying of

Dishes, foods, and culture

Deep-fried foods are common in many countries, and have also been described as "a staple of almost all street cuisines on all continents". There are hundreds of dishes that are associated with deep frying as most foods can be deep-fried. Examples of food that can be deep-fried include meat, poultry, fish and vegetables.

Fish and chips Fish and chips is a popular hot dish consisting of fried fish in crispy batter, served with chips. The dish originated in England, where these two components had been introduced from separate immigrant cultures; it is not known who created ...

, for instance, combines deep-fried fish and deep-fried

potatoes The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern United ...

. French fries,

doughnut A doughnut or donut () is a type of food made from leavened fried dough. It is popular in many countries and is prepared in various forms as a sweet snack that can be homemade or purchased in bakeries, supermarkets, food stalls, and fran ...

s, and

hushpuppies HushPuppies is a French garage rock and indie rock band influenced by the various bands of the 1960s. Members of the group live in Paris, France, although originate from Perpignan and Bordeaux. Members * Singer: Olivier Jourdan * Guitar: Cyr ...

are common deep-fried foods. Other common deep-fried foods include Chinese ''you bing'' deep-fried pancakes, Southeast Asian '' jin deui'', and Japanese tempura. Less common deep-fried foods include

maple leaves The maple leaf is the characteristic leaf of the maple tree. It is the most widely recognized national symbol of Canada. History of use in Canada By the early 1700s, the maple leaf had been adopted as an emblem by the French Canadians along t ...

, peanut butter and jelly sandwiches,

pizza Pizza (, ) is a dish of Italian origin consisting of a usually round, flat base of leavened wheat-based dough topped with tomatoes, cheese, and often various other ingredients (such as various types of sausage, anchovies, mushrooms, ...

, and

Snickers Snickers is a chocolate bar made by the American company Mars, Incorporated, consisting of nougat topped with caramel and peanuts that is encased in milk chocolate. The annual global sales of Snickers was over $3 billion . In the United Ki ...

bars. In the United States, the ''Chicago Tribune'' notes that "you can deep fry almost anything". The American South has been noted as a modern center of innovation in the area of deep-fried food. According to the owner of a deep frying restaurant in the South, "If something is edible, you can bet that someone south of the Mason-Dixon line has tried to cook it in oil". File:Friescookingbigrest.jpeg, alt=A row of five deep fryers, all steaming and filled with baskets of French fries.,

being cooked in a row of deep fryers File:Deep frying chicken upper wing.JPG, alt=Battered chicken legs in bubbling oil., Deep-frying chicken in a pan File:DeepFriedTurkey.jpg, alt=A whole turkey, browned on the outside, on a metal stand., A deep-fried turkey File:Fried Swordfish collar.jpg, Deep-fried

swordfish Swordfish (''Xiphias gladius''), also known as broadbills in some countries, are large, highly migratory predatory fish characterized by a long, flat, pointed bill. They are a popular sport fish of the billfish category, though elusive. Swordfi ...

collar File:Fried calamari.jpg, alt=Pale breaded rings on a plate., Breaded, deep-fried calamari File:Fried pork intestines.jpg, alt=Skewers with rings of pork intestine, Deep fried chitterlings

Africa

In Northern Africa, deep-fried dishes are a part of the cuisine. A common food in this region is the deep-fried fritter, also referred to as "sponges". In East Africa deep fried food is common, cooked in cast iron or earthenware pots. Frying in batter is common. A Ugandan speciality is a kind of doughnut called Mandazi. In areas of Southern Africa, street foods include deep-fried potato and cassava chips. Deep-fried foods in the country of South Africa include fish and chips, '' vetkoek'' and '' koeksisters'', among others.

Asia

Japanese

is a popular deep-fried food that generally consists of battered and fried seafood and vegetables. Japanese deep-fried dishes, or Agemono, include other styles besides tempura, such as Karaage, Korokke, Kushikatsu, and Tonkatsu. In areas of

Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, south-eastern region of Asia, consistin ...

such as Thailand,

insects Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs ...

are commonly deep-fried for human consumption. Western-style fast food items such as donuts, deep-fried chicken, and deep-fried potatoes are also becoming popular in Asia. In

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...

deep fried food is quite common, serving as either a main dish or a snack. The ingredients are usually deep fried in

palm oil Palm oil is an edible vegetable oil derived from the mesocarp (reddish pulp) of the fruit of the oil palms. The oil is used in food manufacturing, in beauty products, and as biofuel. Palm oil accounted for about 33% of global oils produced fr ...

, the most widely used cooking oil in the country. Some popular deep fried foods include '' ayam goreng'' (chicken), ''

pecel lele Pecel lele or pecak lele is an Indonesian deep-fried ''Clarias'' catfish dish originating from Lamongan, East Java, Indonesia. Dish It consists of catfish served with traditional ''sambal'' chili paste, often served with fried tempeh and/or tof ...

'' (catfish), '' pempek'' (fishcake) and tempeh. Fritters in Indonesia is generally identified as '' gorengan'', the most popular one including ''

pisang goreng A banana fritter is a fritter made by deep frying battered banana or plantain in hot oil. It is a common dish across Southeast Asia and South India,Kerala. Varieties Brunei Banana fritters are a traditional snack in Brunei, where they are ca ...

'' (banana fritter), '' bakwan jagung'' (corn) and '' tahu goreng'' (tofu). Deep-fried fish,

tofu Tofu (), also known as bean curd in English, is a food prepared by coagulating soy milk and then pressing the resulting curds into solid white blocks of varying softness; it can be ''silken'', ''soft'', ''firm'', ''extra firm'' or ''super fi ...

, and ' are commonly eaten in

Vietnamese cuisine Vietnamese cuisine encompasses the foods and beverages of Vietnam. Meals feature a combination of five fundamental tastes ( vi, ngũ vị, links=no, label=none): sweet, salty, bitter, sour, and spicy. The distinctive nature of each dish refle ...

. Deep frying is also used to make several kinds of ', including ' (fried rice ball), ' (sesame ball), ' (hollow doughnut), ' (sweet potato pancake), ' (banana fritter), Hồ Tây–style ' (shrimp fritter), and ' (pillow cake). Deep-fried sticks of dough, known as

youtiao ''Youtiao'' (), known in Southern China as Yu Char Kway is a long golden-brown deep-fried strip of dough of Chinese origin and (by a variety of other names) also popular in other East and Southeast Asian cuisines. Conventionally, ''youtia ...

in Chinese, are eaten in many East and Southeast Asian cuisines. In Hong Kong, deep-fried intestine of pigs is a popular food. In

South Asia South Asia is the southern subregion of Asia, which is defined in both geographical and ethno-cultural terms. The region consists of the countries of Afghanistan, Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan, and Sri Lanka.;;;;; ...

, popular deep fried snacks are samosa, jalebi, and pakora.

Europe

Many countries in Europe use pure or

hydrogenated Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organi ...

rapeseed oil for deep-frying. The deep-fried Mars bar originated in Scotland, with The Carron Fish Bar in Stonehaven claiming to have invented it in the early 1990s.

is a very popular deep-fried dish in England since it originated in London in the 19th century and became popular among the working class. Its popularity continues with 229 million portions of fish and chips being sold annually in England. There is an annual trade fair devoted to deep-fried foods called the International Symposium on Deep-Fat Frying which features discussions on deep fat frying as well as exhibitions by companies involved with the process. Belgian tradition requires

to be deep-fried in filtered fat of

cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Adult females are referred to as cows and adult ...

, locally called ''blanc de boeuf'' or ''ossewit''. The Mediterranean diets traditionally use olive oil for deep-frying, which it is absorbed by the food in the process. Research indicates that virgin olive oil is unique among other cooking oils because it is very rich in monounsaturated fatty acids and contains beneficial micronutrients.

North America

In the United States, soybean oil is often used for deep-frying. Beignets, originally a French dish, are a popular deep-fried pastry in the U.S. city of

New Orleans New Orleans ( , ,New Orleans

Fast food is one of the most common ways to consume deep-fried food in North America. Novelty deep-fried foods are popular today in American fairs, especially those in the American South. Hundreds of items are served at these fairs. Some of them include deep-fried beer, butter, and bubblegum. Additionally, deep frying can be used as a form of artwork by frying non-edible objects, such as

electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

. Artists such as Henry Hargreaves have deep-fried replicas of electronic items such as

iPad The iPad is a brand of iOS and iPadOS-based tablet computers that are developed by Apple Inc. The iPad was conceived before the related iPhone but the iPhone was developed and released first. Speculation about the development, operati ...

Game Boy The is an 8-bit fourth generation handheld game console developed and manufactured by Nintendo. It was first released in Japan on April 21, 1989, in North America later the same year, and in Europe in late 1990. It was designed by the same te ...

s, and

laptops A laptop, laptop computer, or notebook computer is a small, portable personal computer (PC) with a screen and alphanumeric keyboard. Laptops typically have a clam shell form factor with the screen mounted on the inside of the upper l ...

. Deep-fried food contests are frequently held at fairs such as the Texas State Fair, where they hold an annual contest for the most creative deep-fried food. Notable past winners have included fried Coke and deep-fried butter, both invented by

Abel Gonzales Abel Gonzales Jr. (born November 1969), also known as Fried Jesus, is an "extreme fryer" and the five-time winner of Big Tex Choice Awards, an annual contest at the Texas State Fair, and the inventor of several deep fried items including Fried Co ...

. Since 2013, an American reality competition show called ''deep-fried Masters'', produced by Discovery Networks, holds deep frying competitions at several state fairs across the country.

Oceania

Fish and chip shops in Australia may purvey several types of deep-fried foods, along with other food types.

South America

The

buñuelo A ''buñuelo'' (; alternatively called ''boñuelo'', ''bimuelo'', ''birmuelo'', ''bermuelo'', ''bumuelo'', ''burmuelo'', or ''bonuelo''; ca, bunyol, ) is a fried dough fritter found in Spain, Latin America, and other regions with a historical co ...

, a fried dough ball popular in Central America and Greece, is a popular deep-fried

snack A snack is a small portion of food generally eaten between meals. Snacks come in a variety of forms including packaged snack foods and other processed foods, as well as items made from fresh ingredients at home. Traditionally, snacks are ...

and street food in South America. Picarone, a Peruvian dessert originated in the colonial period, are deep-fried doughs made with pumpkin and sweet potatoes, popular in Peru and Chile, especially during harvest festivals., a family of deep fried cakes is well known across, sopaipillas a Chilean bread are deep fried in oil or butter also made with pumpkin, cachangas a Peruvian bread made of flour, salt and

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to consti ...

, known as chipá cuerito in Paraguay and Torta frita in

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, t ...

and

Uruguay Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del Uruguay), is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast; while bordering ...

, made of flour, salt and yeast, sometimes adittioned with milk and animal fat and fried in cow fat, the churro, a fried dough popular in

Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = '' Plus ultra'' ( Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , ...

is a popular fried snack and street food in Argentina and Uruguay, milanesa a deep fried breaded

veal Veal is the meat of calves, in contrast to the beef from older cattle. Veal can be produced from a calf of either sex and any breed, however most veal comes from young male calves of dairy breeds which are not used for breeding. Generally, ...

beef Beef is the culinary name for meat from cattle (''Bos taurus''). In prehistoric times, humankind hunted aurochs and later domesticated them. Since that time, numerous breeds of cattle have been bred specifically for the quality or quant ...

from Argentina, Paraguay and Uruguay.

Oil deterioration and chemical changes

Deep fat frying involves heating oil to temperatures in excess of 180 °C in the presence of moisture and air. These conditions can induce a series of complex chemical reactions which may impact the quality of both the food and the oil it is cooked in. Examples of different chemical reactions include the production of

free radicals In chemistry, a radical, also known as a free radical, is an atom, molecule, or ion that has at least one unpaired valence electron. With some exceptions, these unpaired electrons make radicals highly chemically reactive. Many radicals spon ...

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis ...

, isomerization and

polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...

. The exact reactions are dependent upon factors such as the oil type, frying conditions, and food being cooked. When frying, water can attack the ester linkage of triacylglycerols, resulting in mono- and diglycerols, glycerol, and free fatty acids (a type of

reaction). The aforementioned hydrolysis reaction is enhanced by the produced

fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, ...

s and other low molecular weight acid compounds. Overheating or over-using the frying oil leads to formation of rancid-tasting products of

, and other deleterious, unintended or even toxic compounds such as acrylamide (from

starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets ...

y foods). Recent research suggests fat deterioration may be worse when fat or oil is fried with food than when fat or oil is tested on its own in a laboratory. Deep-frying under vacuum helps to significantly reduce acrylamide formation, but this process is not widely used in the

food industry The food industry is a complex, global network of diverse businesses that supplies most of the food consumed by the world's population. The food industry today has become highly diversified, with manufacturing ranging from small, traditional, ...

due to the high investment cost involved. Some useful tests and indicators of excessive oil deterioration are the following: * Sensory – darkening, smoke, foaming, thickening, rancid taste and unpleasant smell when heating. This is the most unreliable way to decide when to change oil because those are very individual factors and can depend on different causes. * Testing strips – decide when to change oil depending on FFA (

free fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, f ...

s) only * Oil-tester – measurement tool to exactly define the point of change oil by TPM/TPC (Total polar material/compounds) * Laboratory –

acidity In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...

anisidine value ''p''-Anisidine (or ''para''-anisidine) is an organic compound with the formula CH3OC6H4NH2. A white solid, commercial samples can appear grey-brown owing to air oxidation. It is one of three isomers of anisidine, methoxy-containing anilines. I ...

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

, total polar compounds, polymeric

triglycerides A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and '' glyceride''). Triglycerides are the main constituents of body fat in humans and other vertebrates, as ...

. Instruments that indicate total polar compounds, currently the best single gauge of how deep-fried an object is, are available with sufficient accuracy for restaurant and industry use.

Hazards

Cooking oil is

flammable A combustible material is something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...

, and fires may be caused by it igniting at too high a temperature. Further, attempts to extinguish an oil fire with water can cause an extremely dangerous condition, a

boilover file:Fettbrandsequenz.jpg, upright=1.5, Fire fighters simulating boilover to demonstrate the risks. Length of the sequence 2.4 seconds. it was 1 kg cooking oil and 1 litre of water. A boilover (or boil-over) type of fire refers to an extremel ...

, as they cause the water to flash into steam due to the high heat of the oil, in turn sending the burning oil in all directions and thus aggravating the fire. This is the leading cause of house fires in the United Kingdom. Instead, oil fires must be extinguished with a non-water

fire extinguisher A fire extinguisher is a handheld active fire protection device usually filled with a dry or wet chemical used to extinguish or control small fires, often in emergencies. It is not intended for use on an out-of-control fire, such as one which ha ...

or by

smothering Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can i ...

. Other means of extinguishing an oil fire include application of dry powder (e.g.,

baking soda Sodium bicarbonate ( IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation ( Na+) and a bicarbonate anion ( HCO3� ...

, salt) or

fire fighting foam Firefighting foam is a foam used for fire suppression. Its role is to cool the fire and to coat the fuel, preventing its contact with oxygen, thus achieving suppression of the combustion. Firefighting foam was invented by the Russian engineer a ...

. Most commercial deep fryers are equipped with automatic fire suppression systems using foam. Spilled hot cooking oil can also cause severe third degree burns, In the worst-case scenario, severe burns can be fatal. The higher temperatures and tendency of oil to stick to the skin make spilled hot cooking oil far more dangerous than spilled hot water. Children can accidentally place their hands on top of the stove, playing with the materials while being cooked, or accidentally pull the pot down, which can cause significant injury. If children are present, the utmost care should be used when deep frying so that their safety can be protected at all times.

Environmental

Deep frying produces large amounts of waste oil, which must be disposed of properly. Waste oil can contribute to the creation of fatbergs, overflow sewage systems, bind to the walls of sewage pipes, and interfere with sewage treatment. Waste oil from deep frying is increasingly being recycled and refined into

biodiesel Biodiesel is a form of diesel fuel derived from plants or animals and consisting of long-chain fatty acid esters. It is typically made by chemically reacting lipids such as animal fat ( tallow), soybean oil, or some other vegetable oil ...

. The heating element in a deep fryer consumes enormous energy, electricity or otherwise. According to one source, an average home appliance deep fryer draws 2,000 watts. Potatoes that are stored in artificially humidified warehouses contain more water, which makes the time required to deep fry them into chips longer. This increases the carbon dioxide footprint of commercially producing chips because more energy is required for frying over a longer time.

Health

The process of deep frying food is generally detrimental to its nutritional value. The oils that foods absorb in their batter typically contain large amounts of

saturated fat A saturated fat is a type of fat in which the fatty acid chains have all single bonds. A fat known as a glyceride is made of two kinds of smaller molecules: a short glycerol backbone and fatty acids that each contain a long linear or branched ...

s and

trans fat Trans fat, also called trans-unsaturated fatty acids, or trans fatty acids, is a type of unsaturated fat that naturally occurs in small amounts in meat and milk fat. It became widely produced as an unintentional byproduct in the industrial p ...

s. Consumption of large amounts of saturated and trans fats has been linked to a higher risk for some

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...

s. Eating deep-fried foods has also been linked to higher

cholesterol Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell membr ...

levels,

obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's ...

, heart attacks, and

diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level (hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...

. Deep-fried foods cooked at certain temperatures can also contain acrylamide. This discovery in 2002 led to international health concerns. Subsequent research has however found that it is not likely that the acrylamides in burnt or well-cooked food cause cancer in humans;

Cancer Research UK Cancer Research UK (CRUK) is the world's largest independent cancer research organization. It is registered as a charity in the United Kingdom and Isle of Man, and was formed on 4 February 2002 by the merger of The Cancer Research Campaign and t ...

categorizes the idea that burnt food causes cancer as a "myth". Additionally, fat degradation processes ( lipid peroxidation) during deep frying results in the loss of nutritional value in deep-fried foods. Cooking oil that has been used for too long may in addition cause blood pressure elevation and vascular hypertrophy. Trans fats are used in shortenings for deep-frying in restaurants, as they can be used for longer than most conventional oils before becoming rancid. In the early 21st century, non-hydrogenated vegetable oils that have lifespans exceeding that of the frying shortenings became available. As fast-food chains routinely use different fats in different locations, trans fat levels in fast food can have large variations. The amount of trans fat that is formed during frying appears to increase with frying temperature, frying time, oil oxidation, and oil reuse. Some studies have found that deep frying in olive and sunflower oils has been found to be less of a detriment to health and in some cases have positive effects on

insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabol ...

levels. Oil can be reused a few times after original use after straining out solids. However, excessive use of the same oil can cause it to break down and release compounds into the food that may be carcinogenic, affect liver health, or influence the body's ability to absorb vitamins. Some European countries have set public health standards for the safety of frying oil.

References

External links

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Deep Fried Twinkies Mix

deep Fried Oreos Mix
{{DEFAULTSORT:Deep Frying Cooking techniques Food preparation techniques Culinary terminology