Cooking warms food, and also transforms it at a chemical level. This chemical transformation of flavor, texture, and appearance is one of the great cultural arts, and can be achieved by applying heat by a variety of methods, and also by straight chemical reactions (ceviche, for example, is created by “cooking” fish in the acids found in citrus juice.) Cooking affects both the nutritional properties and safety of food; improperly prepared foods may lose important nutrients or may be riddled with dangerous bacteria. Cooking can be considered a science, as there are basic techniques that will create standard results, or an art, as many chefs—both professional and amateur—express their creativity through this medium. Also, as techniques and ingredients vary from location to location, cooking is also a marker that echoes each individual society’s history, culture, and ethnicity.
The earliest type of cooking was roasting, directly in a fire. There is archaeological evidence of roasted foodstuffs, both animal and vegetable, in human (Homo erectus) campsites dating from the first known use of fire some 800,000 years ago. Many important cookery techniques require boiling of water in a fire-proof pot, a practice that dates back at least since the 10th millennium BC with the introduction of pottery.
Effects of cooking
With the application of heat, foods can experience changes in their shape, texture, color, and flavor. Nutrients each react differently to heat. When temperatures reach between 160˚ and 185˚F, proteins begin to lose their moisture content and solidify in a process called coagulation. For example, when an egg white is added to a hot frying pan, you can see it change from a clear liquid into a solid white. Starches, which are complex carbohydrates, undergo the process of gelatinization. Gelatinization refers to the absorption of water that leads to swelling and softening, such as when rice is cooked. Gelatinization occurs over a broader range of temperatures than coagulation, between 150˚-212˚F. Simple carbohydrates called sugars undergo a process called caramelization, or browning, at very high temperatures. Caramelization is responsible for many of the flavors we experience, an integral processes in cooking meats, vegetables, breads, sauces, and desserts.
Heat can kill or inactivate organisms including bacteria and viruses. Whether or not heating actually does this depends on just how high the temperature of the food becomes, and how long it is heated. Techniques also come into play.
The temperature range from 4°C to 57°C (41°F to 135°F) is the "food danger zone." Between these temperatures bacteria can grow rapidly. Under the correct conditions bacteria 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.
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 are far less likely to harbor bacteria.  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 dilute bleach (1 Tbsp/gal water), or a trip through the dishwasher, are effective methods for reducing the risk of illness due to contaminated cooking implements.
Food groups and categories
Much edible animal material is made of proteins, including muscle, offal, and egg white. Nutritionally, these animal products offer all the essential amino acids needed in our diet. Almost all vegetable matter also includes proteins (although generally in smaller amounts). Vegetables are also a source of essential amino acids, but generally must be eaten in combination to provide the full range of essential amino acids. When proteins are heated to near boiling point they become de-natured 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 production of stable foams using egg whites. These are believed to be formed through the partial unraveling of the albumen protein molecules in response to beating with a whisk. 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.
Fats and oils come from both animal and plant sources. In cooking, fats provide tastes and textures but probably the most significant attribute is the wide range of cooking temperatures that can be provided by using a fat as the principal cooking medium rather than water. Commonly used fats and oils include butter, olive oil, sunflower oil, lard, beef fat - both dripping or tallow, rapeseed oil or Canola, and peanut oil. The inclusion of fats tend to add flavour to cooked food even though the taste of the oil on its own is often unpleasant. This fact has encouraged the popularity of high fat foods many of which are classified as junk food such as hamburgers or convenience fried cereal snacks. Fats can also be blended with cereal flours to make a range of doughs and pastries. Roux made with heated fat and flour can also absorb large volumes of water-based liquids, including milk and water itself to form smooth sauces. This relies on the properties of starches to create simpler mucilaginous saccharides during cooking, which causes the familiar thickening of sauces.
Carbohydrates used in cooking include a variety of sugars and starches including cereal flour, rice, arrowroot, and potato. Long chain sugars such as starch tend to break down into more simple sugars when cooked or made more acidic, such as with lemon juice or vinegar. 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.
For a comprehensive list of cooking techniques click here. Heat is the primary form of energy used to cook foods. When something gets hot, its molecules absorb the heat energy causing them to vibrate rapidly. This causes them to expand and bounce off of each other causing the heat energy to transfer. As the molecules move faster, the temperature gets higher. Heat based cooking techniques transfer energy to foods using conduction, convection, or radiation. Once the heat reaches the food, it continues through the food using conduction.
Conduction refers to the transfer of heat from one object to another through direct contact. For example, when the heat from a stove top burner touches the bottom of a frying pan, that heat is transferred to the pan. In turn, the heat is then transferred from the metal of the pan to surface of the food resting in the pan. Different materials make better conductors, copper and aluminium being the best. Conduction is a relatively slow method of heat transfer because of the need for physical contact.
Heat that is transferred through a liquid is called convection. Convection occurs when heat is transferred through a medium to a liquid via conduction, causing the molecules of the liquid to move from a warmer location to a cooler one. There are two types of convection - natural and mechanical. Natural convection refers to the circulation of heat caused by the tendency for warm liquids to rise and cooler liquids to fall. When a pot of water is placed on a burner, the molecules on the bottom of the pot are warmed first, causing them to rise to the top. They are replaced by the cooler molecules at the top of the pot, which are then warmed and repeats the cycle, transferring the heat throughout the pot. Mechanical convection uses a fan or stirring to circulate the heat more quickly.
Radiation differs from conduction and convection, in that it does not require physical contact to transfer heat. Instead it is transferred by waves of heat or light hitting the food. There are two forms of radiation used in cooking - infrared and microwave. Infrared radiation occurs when a heating element is heated to a very high temperature, sending out waves of heat to cook the food. Toasters and broilers are two pieces of equipment that use this method. Microwaving occurs in a special oven called a microwave. Microwaving is a very fast cooking method due to the deep penetration of heat.
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) and Pierre Gagnaire (chef). Food science has also been brought to the mainstream by popular television chef Alton Brown in his show Good Eats, in which Brown discusses the scientific reasons why different techniques or ingredients beget various results (such as why the molecules in cooking oil create a softer chewier cookie while using butter in the same recipe will create a crisper, firmer one.)
Raw Foods Movement
Mention raw food to most people and they will immediately think of the Japanese dish of Sushi. But that couldn't be further from the truth for members of the fast-growing 'Raw Food Movement'. Seeds, along with nuts, legumes, fresh fruits and vegetables will form the basis of your daily diet - all eaten uncooked.
On the west coast of the USA, Hollywood stars are embracing and popularizing the movement. This is evidenced by the growing number of raw food restaurants opening in California (U.S. state). The UK, Europe and Australia are also seeing an emergence of the movement.
Health is given as the reason to follow such a diet, but eating, for example, raw potatoes, is not necessarily such a healthy exercise. Potatoes are members of the Solanacae family, plants which contain potentially toxic alkaloids called solanine. Cooking a potato destroys the solanine, eating raw potatoes puts it into your body.
Whether a meat-eater or not, we still need protein for our bodies to perform. Raw Foodists get their protein from foodstuffs like lentils, chickpeas, tofu, peas, peanut butter, soy milk, almonds, spinach, rice, whole wheat bread, potatoes, broccoli and kale.
Vitamin D is noticeably lacking from a raw food diet. In summer this isn't a problem. Fifteen minutes or so in the sun will provide the required daily dose of Vitamin D. In winter, juices, soy milk and rice mik fortified with Vitamin D will fulfill the requirement.