Cooking

Cooking or cookery is the, , and  of preparing  for consumption. Cooking techniques and ingredients vary widely across the, from grilling food over an open fire to using s, to baking in various types of s, reflecting unique environmental, economic, and cultural traditions and trends. Types of cooking also depend on the skill levels and training of cooks. Cooking is done both by people in their own dwellings and by professional cooks and chefs in restaurants and other food establishments. Cooking can also occur through chemical reactions without the presence of heat, such as in, a traditional n dish where is cooked with the acids in  or lime juice.

Preparing food with heat or fire is an activity unique to humans. It may have started around 2 million years ago, though archaeological evidence for it reaches no more than 1 million years ago.

The expansion of agriculture, commerce, trade, and transportation between civilizations in different regions offered cooks many new ingredients. New inventions and technologies, such as the invention of for holding and boiling water, expanded cooking techniques. Some modern cooks apply advanced scientific techniques to food preparation to further enhance the flavor of the dish served.

History
suggests that human ancestors may have invented cooking as far back as 1.8 million to 2.3 million years ago. Re-analysis of burnt bone fragments and plant ashes from the in South Africa has provided evidence supporting  by 1 million years ago. There is evidence that  was cooking their food as early as 500,000 years ago. Evidence for the controlled use of fire by Homo erectus beginning some 400,000 years ago has wide scholarly support. Archaeological evidence from 300,000 years ago, in the form of ancient hearths, s, burnt animal bones, and, are found across Europe and the Middle East. s think that widespread cooking fires began about 250,000 years ago when s first appeared.

Recently, the earliest hearths have been reported to be at least 790,000 years old.

Communication between the Old World and the New World in the influenced the history of cooking. The movement of foods across the Atlantic from the New World, such as es, es,, s, , , , , , , , , , , , , , s, and , had a profound effect on Old World cooking. The movement of foods across the Atlantic from the Old World, such as, , s, , s, , , s, s, s, s, s, , and s, similarly changed New World cooking.

In the seventeenth and eighteenth centuries, food was a classic marker of identity in Europe. In the nineteenth-century "Age of " cuisine became a defining symbol of national identity.

The brought mass-production, mass-marketing, and standardization of food. Factories processed, preserved, canned, and packaged a wide variety of foods, and processed cereals quickly became a defining feature of the American breakfast. In the 1920s,, s, and s emerged.

Starting early in the 20th century, governments issued nutrition guidelines that led to the (introduced in Sweden in 1974). The 1916 "Food For Young Children" became the first USDA guide to give specific dietary guidelines. Updated in the 1920s, these guides gave shopping suggestions for different-sized families along with a Depression Era revision which included four cost levels. In 1943, the USDA created the "Basic Seven" chart to promote nutrition. It included the first-ever Recommended Daily Allowances from the National Academy of Sciences. In 1956, the "Essentials of an Adequate Diet" brought recommendations which cut the number of groups that American school children would learn about down to four. In 1979, a guide called "Food" addressed the link between excessive amounts of unhealthy foods and chronic diseases. Fats, oils, and sweets were added to the four basic food groups.

Ingredients
Most ingredients in cooking are derived from. Vegetables, fruits, grains and nuts as well as herbs and spices come from plants, while meat, eggs, and dairy products come from animals. Mushrooms and the yeast used in baking are kinds of. Cooks also use and s such as. Cooks can also use or.

Naturally occurring ingredients contain various amounts of molecules called , s and s. They also contain water and minerals. Cooking involves a manipulation of the chemical properties of these molecules.

Carbohydrates
Carbohydrates include the common sugar, (table sugar), a, and such simple sugars as  (made by enzymatic splitting of sucrose) and  (from fruit), and es from sources such as cereal flour, rice,  and potato.

The interaction of heat and carbohydrate is complex. such as tend to break down into  when cooked, while simple sugars can form s. If sugars are heated so that all water of  is driven off, then  starts, with the sugar undergoing thermal decomposition with the formation of, and other breakdown products producing. Similarly, the heating of sugars and proteins elicits the, a basic flavor-enhancing technique.

An of starch with fat or water can, when gently heated, provide thickening to the dish being cooked. In cooking, a mixture of butter and flour called a  is used to thicken liquids to make stews or sauces. In Asian cooking, a similar effect is obtained from a mixture of rice or and water. These techniques rely on the properties of starches to create simpler mucilaginous s during cooking, which causes the familiar thickening of s. This thickening will break down, however, under additional heat.

Fats
Types of fat include s, animal products such as butter and, as well as fats from grains, including and  oils. Fats are used in a number of ways in cooking and baking. To prepare, or s, the pan or griddle is often coated with fat or oil. Fats are also used as an ingredient in baked goods such as cookies, cakes and pies. Fats can reach temperatures higher than the boiling point of water, and are often used to conduct high heat to other ingredients, such as in frying, deep frying or sautéing. Fats are used to add flavor to food (e.g., butter or bacon fat), prevent food from sticking to pans and create a desirable texture.

Proteins
Edible animal material, including, , milk, and s, contains substantial amounts of protein. Almost all vegetable matter (in particular s and s) also includes proteins, although generally in smaller amounts. Mushrooms have high protein content. Any of these may be sources of s. When s are heated they become (unfolded) and change texture. In many cases, this causes the structure of the material to become softer or more – meat becomes cooked and is more friable and less flexible. In some cases, proteins can form more rigid structures, such as the coagulation of in egg whites. The formation of a relatively rigid but flexible matrix from egg white provides an important component in baking cakes, and also underpins many desserts based on.

Water
Cooking often involves water, frequently present in other liquids, which is both added in order to immerse the substances being cooked (typically water, or wine), and released from the foods themselves. A favorite method of adding flavor to dishes is to save the liquid for use in other recipes. Liquids are so important to cooking that the name of the cooking method used is often based on how the liquid is combined with the food, as in, , , and. Heating liquid in an open container results in rapidly increased, which s the remaining and ingredients – this is a critical component of both  and sauce making.

Vitamins and minerals
Vitamins and minerals are required for normal  but which the body cannot manufacture itself and which must therefore come from external sources. Vitamins come from several sources including fresh fruit and vegetables, carrots, , cereal bran, bread, liver (B vitamins), fish liver oil  and fresh green vegetables. Many minerals are also essential in small quantities including iron,, , and ; and in very small quantities copper,  and. The micronutrients, minerals, and vitamins in fruit and vegetables may be destroyed or eluted by cooking. Vitamin C is especially prone to oxidation during cooking and may be completely destroyed by protracted cooking. The bioavailability of some vitamins such as, , , , and s are increased with cooking by being freed from the food microstructure. Blanching or steaming vegetables is a way of minimizing vitamin and mineral loss in cooking.

Methods
There are very many methods of cooking, most of which have been known since antiquity. These include baking, roasting, frying, grilling, barbecuing, smoking, boiling, steaming and braising. A more recent innovation is microwaving. Various methods use differing levels of heat and moisture and vary in cooking time. The method chosen greatly affects the end result because some foods are more appropriate to some methods than others. Some major hot cooking techniques include:


 * Roasting


 * Baking


 * Boiling


 * Frying


 * Steaming
 * works by boiling water continuously, causing it to vaporise into steam; the steam then carries heat to the nearby food, thus cooking the food. By many it is considered a healthy form of cooking, holding nutrients within the vegetable or meat being cooked.
 * – The food is put into a pouch and then baked, allowing its own moisture to steam the food.


 * Smoking
 * is the process of flavoring, cooking, or preserving food by exposing it to smoke from burning or smoldering material, most often wood.

Food safety
Cooking can prevent many es that would otherwise occur if the food is eaten raw. When heat is used in the preparation of food, it can kill or inactivate harmful organisms, such as bacteria and viruses, as well as various parasites such as s and . and other illness from uncooked or poorly prepared food may be caused by bacteria such as of ', ' and ', viruses such as es, and  such as '. Bacteria, viruses and parasites may be introduced through salad, meat that is uncooked or done, and unboiled water.

The effect of cooking depends on temperature, cooking time, and technique used. Some bacteria such as ' or ' can form spores that survive boiling, which then germinate and regrow after the food has cooled. This makes it unsafe to reheat cooked food more than once.

Cooking increases the digestibility of many foods which are inedible or poisonous when raw. For example, raw cereal grains are hard to digest, while s are toxic when raw or improperly cooked due to the presence of, which is inactivated by cooking for at least ten minutes at 100 C.

Food safety depends on the safe preparation, handling, and storage of food. Food spoilage bacteria proliferate in the "" temperature range from 40 to 140 F, food therefore should not be stored in this temperature range. Washing of hands and surfaces, especially when handling different meats, and keeping raw food separate from cooked food to avoid cross-contamination, are good practices in food preparation. Foods prepared on plastic cutting boards may be less likely to harbor bacteria than wooden ones. Washing and cutting boards, especially after use with raw meat, poultry, or seafood, reduces the risk of contamination.

Effects on nutritional content of food
Proponents of argue that cooking food increases the risk of some of the detrimental effects on food or health. They point out that during cooking of vegetables and fruit containing, the vitamin elutes into the cooking water and becomes degraded through oxidation. Peeling vegetables can also substantially reduce the vitamin C content, especially in the case of potatoes where most vitamin C is in the skin. However, research has shown that in the specific case of s a greater proportion is absorbed from cooked vegetables than from raw vegetables.

German research in 2003 showed significant benefits in reducing breast cancer risk when large amounts of raw vegetable matter are included in the diet. The authors attribute some of this effect to heat-labile s., a breakdown product, which may be found in vegetables such as , has been shown to be protective against , however, much of it is destroyed when the vegetable is boiled.

The has studied retention data for 16 vitamins, 8 minerals, and alcohol for approximately 290 foods for various cooking methods.

Carcinogens
In a human epidemiological analysis by and  in 1981, diet was estimated to cause a large percentage of cancers. Studies suggest that around 32% of cancer deaths may be avoidable by changes to the diet. Some of these cancers may be caused by carcinogens in food generated during the cooking process, although it is often difficult to identify the specific components in diet that serve to increase cancer risk. Many foods, such as beef steak and broccoli, contain low concentrations of both s and s.

Several studies published since 1990 indicate that cooking meat at high temperature creates s (HCAs), which are thought to increase cancer risk in humans. Researchers at the found that human subjects who ate beef rare or medium-rare had less than one third the risk of stomach cancer than those who ate beef medium-well or well-done. While avoiding meat or eating meat raw may be the only ways to avoid HCAs in meat fully, the National Cancer Institute states that cooking meat below 212 F creates "negligible amounts" of HCAs. Also, meat before cooking may reduce HCAs by 90% by reducing the time needed for the meat to be cooked at high heat. s are found in some food, and may be produced by some cooking processes from proteins or from nitrites used as food preservatives; cured meat such as bacon has been found to be carcinogenic, with links to colon cancer. , which is added to cured meat, however, reduces nitrosamine formation.

Research has shown that grilling, barbecuing and smoking meat and fish increases levels of carcinogenic s (PAH). In Europe, grilled meat and smoked fish generally only contribute a small proportion of dietary PAH intake since they are a minor component of diet – most intake comes from cereals, oils and fats. However, in the US, grilled/barbecued meat is the second highest contributor of the mean daily intake of a known PAH carcinogen at 21% after ‘bread, cereal and grain’ at 29%.

Baking, grilling or broiling food, especially starchy foods, until a toasted crust is formed generates significant concentrations of, a known from animal studies; its potential to cause cancer in humans at normal exposures is uncertain. Public health authorities recommend reducing the risk by avoiding overly browning starchy foods or meats when frying, baking, toasting or roasting them.

Other health issues
Cooking dairy products may reduce a protective effect against colon cancer. Researchers at the suggest that ingesting uncooked or unpasteurized s (see also ) may reduce the risk of. Mice and rats fed uncooked sucrose, casein, and beef tallow had one-third to one-fifth the incidence of as the mice and rats fed the same ingredients cooked. This claim, however, is contentious. According to the, health benefits claimed by raw milk advocates do not exist. "The small quantities of antibodies in milk are not absorbed in the human intestinal tract," says Barbara Ingham, PhD, associate professor and extension food scientist at the University of Wisconsin-Madison. "There is no scientific evidence that raw milk contains an anti-arthritis factor or that it enhances resistance to other diseases."

Heating sugars with proteins or fats can produce s ("glycotoxins").

Deep fried food in restaurants may contain high level of, which is known to increase levels of that in turn may increase risk of  and other conditions. However, many fast food chains have now switched to trans-fat-free alternatives for deep-frying.

Scientific aspects
The application of to cooking and  has become known as. This is a subdiscipline of. Important contributions have been made by scientists, chefs and authors such as (chemist),  (physicist),  (physicist),  (author),  (biochemist, author),  (chef),  (chef),  (chemist, author) and  (chef).

Chemical processes central to cooking include the – a form of non-enzymatic browning involving an amino acid, a reducing sugar and heat.

Home-cooking and commercial cooking
Home cooking has traditionally been a process carried out informally in a home or around a, and can be enjoyed by all members of the family, although in many cultures women bear primary responsibility. Cooking is also often carried out outside of personal quarters, for example at restaurants, or schools. were one of the earliest forms of cooking outside the home, and bakeries in the past often offered the cooking of pots of food provided by their customers as an additional service. In the present day, factory food preparation has become common, with many "ready-to-eat" foods being prepared and cooked in factories and home cooks using a mixture of, and factory made foods together to make a. The nutritional value of including more commercially prepared foods has been found to be inferior to home-made foods. Home-cooked meals tend to be healthier with fewer calories, and less, and  on a per calorie basis while providing more , , and. The ingredients are also directly sourced, so there is control over authenticity, taste, and nutritional value. The superior nutritional quality of home-cooking could therefore play a role in preventing. Cohort studies following the elderly over 10 years show that adults who cook their own meals have significantly lower mortality, even when controlling for confounding variables.

"Home-cooking" may be associated with, and some commercially produced foods and restaurant meals are presented through advertising or as having been "home-cooked," regardless of their actual origin. This trend began in the 1920s and is attributed to people in urban areas of the U.S. wanting homestyle food even though their schedules and smaller kitchens made cooking harder.