Cooking

Cooking is the process of preparing food with heat. Cooks select and combine ingredients using a wide range of tools and methods. In the process, the flavor, texture, appearance, and chemical properties of the ingredients can change.

Cooking techniques and ingredients vary widely across the world, reflecting unique environmental, economic, and cultural traditions. Cooks themselves also vary widely in skill and training.

Preparing food with heat or fire is an activity unique to humans, and some scientists believe the advent of cooking played an important role in human evolution. Most anthropologists believe that cooking fires first developed around 250,000 years ago.

The development of agriculture, commerce and transportation between civilizations in different regions offered cooks many new ingredients. New inventions and technologies, such as pottery for holding and boiling water, expanded cooking techniques. Some modern cooks apply advanced scientific techniques to food preparation.

History of cooking

There is no clear evidence as to when cooking was invented. Primatologist Richard Wrangham stated that cooking was invented as far back as 1.8 million to 2.3 million years ago. Other researchers believe that cooking was invented as late as 40,000 or 10,000 years ago. Evidence of fire is inconclusive as wildfires started by lightning-strikes are still common in East Africa and other wild areas, and it is difficult to determine when fire was first used for cooking, as opposed to just being used for warmth or for keeping predators away. Most anthropologists contend that cooking fires began in earnest barely 250,000 years ago, when ancient hearths, earth ovens, burnt animal bones, and flint appear across Europe and the middle East. The only evidence of human use of fire more than two million years ago is burnt earth with human remains, which most anthropologists consider coincidence rather than evidence of intentional fire.

However, some Fire-cracked rock, such as that in Central Texas (United States) are burned rock middens, or enormous piles fire-damaged rock dated to c. 3,500 years ago. These may represent the remains of earth ovens used in cooking since they contain evidence of Dasylirion wheeleri bulbs and other plants. In Great Britain similar Neolithic, Bronze Age and Iron Age features exist, but are commonly called 'burnt mounds'.

Ingredients in cooking
Most ingredients in cooking are derived from living things. Vegetables, fruits, grains and nuts come from plants, while meat, eggs, and dairy products come from animals. Mushrooms and the yeast used in baking are kinds of fungi. Cooks also utilize water and minerals such as salt. Cooks can also use wine, an alcohol-based liquid from the fermentation of juices of grapes or other fruits.

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

Proteins
Edible animal material, including muscle, offal, milk, eggs and egg whites, contains substantial amounts of protein. Almost all vegetable matter (in particular legumes and seeds) also includes proteins, although generally in smaller amounts. These may also be a source of essential amino acids. When proteins are heated they become denatured and change texture. In many cases, this causes the structure of the material to become softer or more friable - meat becomes cooked. In some cases, proteins can form more rigid structures, such as the coagulation of albumen in egg whites. The formation of a relatively rigid but flexible matrix from egg white provides an important component of much cake cookery, and also underpins many desserts based on meringue.

Carbohydrates
Carbohydrates include the common sugar, sucrose (table sugar), a disaccharide, and such simple sugars as glucose (from the digestion of table sugar) and fructose (from fruit), and starches from sources such as cereal flour, rice, arrowroot, potato. The interaction of heat and carbohydrate is complex.

Long-chain sugars such as starch tend to break down into simpler sugars when cooked, while simple sugars can form syrups. If sugars are heated so that all water of crystallization is driven off, then caramelization starts, with the sugar undergoing thermal decomposition with the formation of carbon, and other breakdown products producing caramel. Similarly, the heating of sugars and proteins elicits the Maillard reaction, a basic flavor-enhancing technique.

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

Fats
Types of fat include vegetable oils and animal products such as butter and lard. 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 or sautéing.

Water
Cooking often involves water which is frequently present as other liquids, both added in order to immerse the substances being cooked (typically water, stock or wine), and released from the foods themselves. Liquids are so important to cooking that the name of the cooking method used may be based on how the liquid is combined with the food, as in steaming, simmering, boiling, braising and blanching. Heating liquid in an open container results in rapidly increased evaporation, which concentrates the remaining flavor and ingredients - this is a critical component of both stewing and sauce making.

Vitamins and minerals
Vitamins are materials required for normal metabolism but which the body cannot manufacture itself and which must therefore come from soil. Vitamins come from a number of sources including fresh fruit and vegetables (Vitamin C), carrots, liver (Vitamin A), cereal bran, bread, liver e ( B vitamins), fish liver oil (Vitamin D) and fresh green vegetables (Vitamin K). Many minerals are also essential in small quantities including iron, calcium, magnesium and sulphur; and in very small quantities copper, zinc and selenium. The micronutrients, minerals, and vitamins[4] 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.

Cooking methods

Methods of cooking
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. Some foods are more appropriate to some methods than others. Some major hot cooking techniques include:
Roasting
Roasting - Barbecuing - Grilling - Rotisserie - Searing
Baking
Baking - Baking Blind - Broiling - Flashbaking
Boiling
Boiling - Blanching - Braising - Coddling - Double steaming - Infusion - Poaching - Pressure cooking - Simmering - Steaming - Steeping - Stewing - Vacuum flask cooking
Frying
Frying - Deep frying - Hot salt frying - Hot sand frying - Pan frying - Pressure frying - Sautéing - Stir frying
Smoking
Food smoking

Food safety
Main article: Food safety
When heat is used in the preparation of food, it can kill or inactivate potentially harmful organisms including bacteria and viruses.

The effect will depend on temperature, cooking time, and technique used. The temperature range from 41° F to 135° F (5° C to 57° C) is the "food danger zone." Between these temperatures bacteria can grow rapidly.  Under optimal conditions, E. coli, for example, can double in number every twenty minutes.  The food may not appear any different or spoiled but can be harmful to anyone who eats it.  Meat, poultry, dairy products, and other prepared food must be kept outside of the "food danger zone" to remain safe to eat.  Refrigeration and freezing do not kill bacteria, but only slow their growth. When cooling hot food, it should not be left standing or in a blast chiller for more than 90 minutes.  Cutting boards are a potential breeding ground for bacteria, and can be quite hazardous unless safety precautions are taken.

Plastic cutting boards are less porous than wood and have conventionally been assumed to be far less likely to harbor bacteria.  This has been debated, and some research has shown wooden boards are far better.  Washing and sanitizing cutting boards is highly recommended, especially after use with raw meat, poultry, or seafood. Hot water and soap followed by a rinse with an antibacterial cleaner (dilute bleach is common in a mixture of 1 tablespoon per gallon of water, as at that dilution it is considered food safe, though some professionals choose not to use this method because they believe it could taint some foods), or a trip through a dishwasher with a "sanitize" cycle, are effective methods for reducing the risk of illness due to contaminated cooking implements.

Effects on nutritional content of food
Proponents of Raw foodism argue that cooking food increases the risk of some of the detrimental effects on food or health. They point out that the cooking of vegetables and fruit containing vitamin C both elutes the vitamin into the cooking water and degrades the vitamin 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 also suggested that a greater proportion of nutrients present in food is absorbed from cooked foods than from uncooked foods.

Baking, grilling or broiling food, especially starchy foods, until a toasted crust is formed generates significant concentrations of acrylamide, a possible carcinogen.

Cooking dairy products may reduce a protective effect against colon cancer. Researchers at the University of Toronto suggest that ingesting uncooked or unpasteurized dairy products (see also Raw milk) may reduce the risk of colorectal cancer. Mice and rats fed uncooked sucrose, casein, and beef tallow had one-third to one-fifth the incidence of microadenomas as the mice and rats fed the same ingredients cooked. This claim, however, is contentious.

According to the Food and Drug Administration of the United States, 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, Ph.D., 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."

Several studies published since 1990 indicate that cooking muscle meat creates heterocyclic amines (HCAs), which are thought to increase cancer risk in humans. Researchers at the National Cancer Institute 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 eating muscle meat raw may be the only way to avoid HCAs fully, the National Cancer Institute states that cooking meat below 212 �F (100 �C) creates "negligible amounts" of HCAs. Also, microwaving meat before cooking may reduce HCAs by 90%. Nitrosamines, present in processed and cooked foods, have also been noted as being carcinogenic, being linked to colon cancer.

Research has shown that grilling or barbecuing meat and fish increases levels of carcinogenic Polycyclic aromatic hydrocarbons (PAH). However, meat and fish only contribute a small proportion of dietary PAH intake - most intake comes from cereals, oils and fats. 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 phytonutrients.

Heating sugars with proteins or fats can produce Advanced glycation end products ("glycotoxins"). These have been linked to ageing and health conditions such as diabetes.

Science of cooking
The application of scientific knowledge to cooking and gastronomy has become known as molecular gastronomy. This is a subdiscipline of food science. Important contributions have been made by scientists, chefs and authors such as Herve This (chemist), Nicholas Kurti (physicist), Peter Barham (physicist), Harold McGee (author), Shirley Corriher (biochemist, author), Heston Blumenthal (chef), Ferran Adria (chef), Robert Wolke (chemist, author) and Pierre Gagnaire (chef).

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

Home-cooking vs. factory cooking
Although cooking has traditionally been a process carried out informally at home or around a communal fire, cooking is often, and increasingly, carried out outside the home. Bakeries were an early form of cooking outside the home, and bakeries in the past often offered the cooking of foods provided by their customers as an additional service. In the present day, factory food preparation is rapidly becoming the norm, with many "ready-to-eat" foods being prepared and cooked in factories.

"Home-cooking" may be associated with comfort food, and some commercially produced foods are presented as having been "home-cooked", regardless of their actual origin.