In food processing, brining is treating food with brine or coarse salt which preserves and seasons the food while enhancing tenderness and flavor with additions such as herbs, sugar, caramel and/or vinegar. Meat and fish are brined for less than twenty-four hours while vegetables and fruit are brined in a much longer process known as pickling. Brining is similar to marination, except that a marinade includes a significant amount of acid, such as vinegar or citrus juice. Brining is similar to curing, which involves drying the food, is done over a much longer time period. Brining is a process in which meat is soaked in a salt water solution similar to marination before cooking. Meat is soaked anywhere from 30 minutes to several days; the amount of time needed to brine depends on the size of the meat: More time is needed for a large turkey compared to a broiler fryer chicken. A large roast must be brined longer than a thin cut of meat. Brining can be achieved by covering the meat in dry coarse salt and left to rest for several hours.
The salt draws moisture from the interior of the meat to the surface, where it mixes with the salt and is reabsorbed with the salt brining the meat in its own juices. The salt rub is rinsed off and discarded before cooking. Food scientists have two theories about the brining effect, but which one is correct is still under debate; the brine surrounding the cells has a higher concentration of salt than the fluid within the cells, but the cell fluid has a higher concentration of other solutes. This leads salt ions to diffuse into the cell, while the solutes in the cells cannot diffuse through the cell membranes into the brine; the increased salinity of the cell fluid causes the cell to absorb water from the brine via osmosis. The salt introduced into the cell denatures its proteins; the proteins coagulate, forming a matrix that holds them during cooking. This prevents the meat from dehydrating; as opposed to dry salting, fish brining or wet-salting is performed by immersion of fish into brine, or just sprinkling it with salt without draining the moisture.
To ensure long-term preservation, the solution has to contain at least 20% of salt, a process called "heavy salting" in fisheries. If less salt is used, the fish is suited for immediate consumption, but additional refrigeration is necessary for longer preservation. Wet-salting is used for preparation of: Salted herring, non-gutted, with hard or soft roe and salted, Soused herring, gutted and salted, without roe, which can be immersed in brine or wet-salted. After several years, the fish liquifies and can be processed into paste or anchovy butter and other types of roe. Pickled vegetables are immersed in brine, vinegar or vinaigrette for extended periods of time, where they undergo anaerobic fermentation which affects their texture and flavor. Pickling can preserve perishable foods for months. Antimicrobial herbs and spices, such as mustard seed, cinnamon or cloves, are added. Unlike the canning process, pickling does not require that the food be sterile before it is sealed; the acidity or salinity of the solution, the temperature of fermentation, the exclusion of oxygen determine which microorganisms dominate, determine the flavor of the end product.
Brine is commonly used to age brined cheeses, such as halloumi and feta. Not only does the brine carry flavors into the cheese, but the salty environment may nurture the growth of the Brevibacterium linens bacteria, which can impart a pronounced odor and interesting flavor; the same bacteria can have some effect on cheeses that are ripened in humid conditions, like Camembert. Large populations of these "smear bacteria" show up as a sticky orange-red layer on some brine-washed cheeses. Kosher salt – Coarse edible salt without common additives such as iodine Pickling salt – Fine-grained salt used for manufacturing pickles Curing – Food preservation and flavoring processes based on drawing moisture out of the food by osmosis Brining on Cooking For Engineers - a discussion on what happens to meat as it brines
Halal spelled hallal or halaal, refers to what is permissible or lawful in traditional Islamic law. It is applied to permissible food and drinks. In the Quran, the word halal is contrasted with haram. In Islamic jurisprudence, this binary opposition was elaborated into a more complex classification known as "the five decisions": mandatory, neutral and forbidden. Islamic jurists disagree on whether the term halal covers the first three or the first four of these categories. In recent times, Islamic movements seeking to mobilize the masses and authors writing for a popular audience have emphasized the simpler distinction of halal and haram; the term halal is associated with Islamic dietary laws, meat processed and prepared in accordance with those requirements. The words halal and haram are the usual terms used in the Quran to designate the categories of lawful or allowed and unlawful or forbidden. In the Quran, the root h-l-l denotes lawfulness and may indicate exiting the ritual state of a pilgrim and entering a profane state.
In both these senses, it has an opposite meaning to. In a literal sense, the root h-l-l may refer to alighting. Lawfulness is indicated in the Quran by means of the verb ahalla, with God as the stated or implied subject; the terms halal and haram parallel the Hebrew terms mutar and asur, — with respect to dietary rules — the Old Testament categories of clean and unclean. Several food companies offer halal processed foods and products, including halal foie gras, spring rolls, chicken nuggets, lasagna and baby food. Halal ready meals are a growing consumer market for Muslims in Britain and America and are offered by an increasing number of retailers. Vegetarian cuisine is halal; the most common example of haram food is pork. While pork is the only meat that categorically may not be consumed by Muslims other foods not in a state of purity are considered haram; the criteria for non-pork items include their source, the cause of the animal's death, how it was processed. It depends on the Muslim's madhab.
Muslims must ensure that all foods, as well as non-food items like cosmetics and pharmaceuticals, are halal. These products contain animal by-products or other ingredients that are not permissible for Muslims to eat or use on their bodies. Foods which are not considered halal for Muslims to consume include blood and intoxicants such as alcoholic beverages. A Muslim who would otherwise starve to death is allowed to eat non-halal food if there is no halal food available. At a conference called "Agri-biotechnology: Shariah Compliance" held in Malaysia in December 2010 by the Malaysian Biotechnology Information Centre and International Halal Integrity Alliance, participants "adopted a resolution that accepts GM crops and products as halal should all ingredients used to develop them are from halal sources.... The only Haram cases are limited to products derived from Haram origin retaining their original characteristics that are not changed."An article from 2000 stated: "Should a product be brought to market with a gene from a haram source, today it would at least be considered Mashbooh — questionable — if not outright haram.
However, all biotechnology-derived foods on the market today are from approved sources." Globally, halal food certification has been criticized by anti-halal lobby groups and individuals using social media. Critics have argued. Australian Federation of Islamic Councils spokesman Keysar Trad told a journalist in July 2014 that this was an attempt to exploit anti-Muslim sentiments; the Dubai Chamber of Commerce estimated the global industry value of halal food consumer purchases to be $1.1 trillion in 2013, accounting for 16.6 percent of the global food and beverage market, with an annual growth of 6.9 percent. Growth regions include Turkey; the European Union market for halal food has an estimated annual growth of around 15 percent and is worth an estimated $30 billion. The food must come from a supplier. Dhabīḥah is the prescribed method of slaughter for all meat sources, excluding fish and other sea-life, per Islamic law; this method of slaughtering animals consists of using a well-sharpened knife to make a swift, deep incision that cuts the front of the throat, the carotid artery and jugular veins.
The head of an animal, slaughtered using halal methods is aligned with the qiblah. In addition to the direction, permitted animals should be slaughtered upon utterance of the Islamic prayer Bismillah "in the name of God"; the slaughter can be performed by a Muslim or an adherent of religions traditionally known as People of the Book. Blood must be drained from the veins. Carrion cannot be eaten. Additionally, an animal, strangled, killed by a fall, savaged by a beast of prey, or sacrificed on a stone altar cannot be eaten; the animal may be stunned prior to having its throat cut. The UK Food Standards Agency figures from 2011 suggest that 84% of cattle, 81% o
Salt is a mineral composed of sodium chloride, a chemical compound belonging to the larger class of salts. Salt is present in vast quantities in seawater; the open ocean has about 35 grams of solids per liter of sea water, a salinity of 3.5%. Salt is essential for life in general, saltiness is one of the basic human tastes. Salt is one of the oldest and most ubiquitous food seasonings, salting is an important method of food preservation; some of the earliest evidence of salt processing dates to around 6,000 BC, when people living in the area of present-day Romania boiled spring water to extract salts. Salt was prized by the ancient Hebrews, the Greeks, the Romans, the Byzantines, the Hittites and the Indians. Salt became an important article of trade and was transported by boat across the Mediterranean Sea, along specially built salt roads, across the Sahara on camel caravans; the scarcity and universal need for salt have led nations to go to war over it and use it to raise tax revenues. Salt has other cultural and traditional significance.
Salt is processed from salt mines, by the evaporation of seawater and mineral-rich spring water in shallow pools. Its major industrial products are caustic chlorine. Of the annual global production of around two hundred million tonnes of salt, about 6% is used for human consumption. Other uses include water conditioning processes, de-icing highways, agricultural use. Edible salt is sold in forms such as sea salt and table salt which contains an anti-caking agent and may be iodised to prevent iodine deficiency; as well as its use in cooking and at the table, salt is present in many processed foods. Sodium is an essential nutrient for human health via its role as an osmotic solute. Excessive salt consumption may increase the risk of cardiovascular diseases, such as hypertension, in children and adults; such health effects of salt have long been studied. Accordingly, numerous world health associations and experts in developed countries recommend reducing consumption of popular salty foods; the World Health Organization recommends that adults should consume less than 2,000 mg of sodium, equivalent to 5 grams of salt per day.
All through history, the availability of salt has been pivotal to civilization. What is now thought to have been the first city in Europe is Solnitsata, in Bulgaria, a salt mine, providing the area now known as the Balkans with salt since 5400 BC; the name Solnitsata means "salt works". While people have used canning and artificial refrigeration to preserve food for the last hundred years or so, salt has been the best-known food preservative for meat, for many thousands of years. A ancient salt-works operation has been discovered at the Poiana Slatinei archaeological site next to a salt spring in Lunca, Neamț County, Romania. Evidence indicates that Neolithic people of the Precucuteni Culture were boiling the salt-laden spring water through the process of briquetage to extract the salt as far back as 6050 BC; the salt extracted from this operation may have had a direct correlation to the rapid growth of this society's population soon after its initial production began. The harvest of salt from the surface of Xiechi Lake near Yuncheng in Shanxi, dates back to at least 6000 BC, making it one of the oldest verifiable saltworks.
There is more salt in animal tissues, such as meat and milk, than in plant tissues. Nomads who subsist on their flocks and herds do not eat salt with their food, but agriculturalists, feeding on cereals and vegetable matter, need to supplement their diet with salt. With the spread of civilization, salt became one of the world's main trading commodities, it was of high value to the ancient Hebrews, the Greeks, the Romans, the Byzantines, the Hittites and other peoples of antiquity. In the Middle East, salt was used to ceremonially seal an agreement, the ancient Hebrews made a "covenant of salt" with God and sprinkled salt on their offerings to show their trust in him. An ancient practice in time of war was salting the earth: scattering salt around in a defeated city to prevent plant growth; the Bible tells the story of King Abimelech, ordered by God to do this at Shechem, various texts claim that the Roman general Scipio Aemilianus Africanus ploughed over and sowed the city of Carthage with salt after it was defeated in the Third Punic War.
Salt may have been used for barter in connection with the obsidian trade in Anatolia in the Neolithic Era. Salt was included among funeral offerings found in ancient Egyptian tombs from the third millennium BC, as were salted birds, salt fish. From about 2800 BC, the Egyptians began exporting salt fish to the Phoenicians in return for Lebanon cedar and the dye Tyrian purple. Herodotus described salt trading routes across Libya back in the 5th century BC. In the early years of the Roman Empire, roads were built for the transportation of salt from the salt imported at Ostia to the capital. In Africa, salt was used as currency south of the Sahara, slabs of rock salt were used as coins in Abyssinia. Moorish merchants in the 6th century traded salt for weight for weight; the Tuareg have traditionally maintained routes across the Sahara for the transportation of salt by Azalai. The caravans
Bacon is a type of salt-cured pork. Bacon is prepared from several different cuts of meat from the pork belly or from back cuts, which have less fat than the belly, it is used as a minor ingredient to flavour dishes. Bacon is used for barding and larding roasts game, including venison and pheasant; the word is derived from the Old High German bacho, meaning "buttock", "ham" or "side of bacon", is cognate with the Old French bacon. Meat from other animals, such as beef, chicken, goat, or turkey, may be cut, cured, or otherwise prepared to resemble bacon, may be referred to as, for example, "turkey bacon"; such use is common in areas with significant Jewish and Muslim populations as both religions prohibit the consumption of pork. Vegetarian bacons such as "soy bacon" exist and attract vegetarians and vegans. Bacon is cured through either a process of injecting with or soaking in brine, known as wet curing, or using plain crystal salt, known as dry curing. Bacon brine has added curing ingredients, most notably sodium nitrite, which speed the curing and stabilize color.
Fresh bacon may be dried for weeks or months in cold air, or it may be smoked or boiled. Fresh and dried bacon are cooked before eating by pan frying. Boiled bacon is ready to eat, as is some smoked bacon. Differing flavours can be achieved by using various types of wood, or less common fuels such as corn cobs or peat; this process can take up to eighteen hours, depending on the intensity of the flavour desired. The Virginia Housewife, thought to be one of the earliest American cookbooks, gives no indication that bacon is not smoked, though it gives no advice on flavouring, noting only that care should be taken lest the fire get too hot. In early American history, the curing and smoking of bacon seems to have been one of the few food-preparation processes not divided by gender. Bacon is distinguished from other salt-cured pork by differences in the cuts of meat used and in the brine or dry packing; the terms "ham" and "bacon" referred to different cuts of meat that were brined or packed identically together in the same barrel.
Today, ham is defined as coming from the hind portion of the pig and brine for curing ham includes a greater amount of sugar, while bacon is less sweet, though ingredients such as brown sugar or maple syrup are used for flavor. Bacon is similar to salt pork, which in modern times is prepared from similar cuts, but salt pork is never smoked, has a much higher salt content. For safety, bacon may be treated to prevent trichinosis, caused by Trichinella, a parasitic roundworm which can be destroyed by heating, drying, or smoking. Sodium polyphosphates, such as sodium triphosphate, may be added to make the product easier to slice and to reduce spattering when the bacon is pan-fried. Varieties differ depending on the primal cut. Different cuts of pork are used for making bacon depending on local preferences. Side bacon, or streaky bacon, comes from the pork belly, it has long alternating layers of muscle running parallel to the rind. This is the most common form of bacon in the United States. Pancetta is an Italian form of side bacon, sold unsmoked.
It is rolled up into cylinders after curing, is known for having a strong flavour. Back bacon contains meat from the loin in the middle of the back of the pig, it is a leaner cut, with less fat compared to side bacon. Most bacon consumed in the United Kingdom and Ireland is back bacon. Collar bacon is taken from the back of a pig near the head. Cottage bacon is made from the lean meat from a boneless pork shoulder, tied into an oval shape. Jowl bacon is smoked cheeks of pork. Guanciale is an Italian jowl bacon, seasoned and dry cured but not smoked; the inclusion of skin with a cut of bacon, known as the'bacon rind', though is less common in the English-speaking world. Bacon is served with eggs and sausages as part of a full breakfast; the most common form sold is middle bacon, which includes some of the streaky, fatty section of side bacon along with a portion of the loin of back bacon. In response to increasing consumer diet-consciousness, some supermarkets offer the loin section only; this is sold as short cut bacon and is priced higher than middle bacon.
Both varieties are available with the rind removed. In Canada, the term bacon on its own refers to side bacon. Canadian-style back bacon is a lean cut from the eye of the pork loin with little surrounding fat. Peameal bacon is an unsmoked back bacon, coated in fine-ground cornmeal. Bacon is eaten in breakfasts, such as with cooked eggs or pancakes. Maple syrup is used as a flavouring while curing bacon in Canada; some of the meanings of bacon overlap with the German-language term Speck. Germans use the term bacon explicitly for Frühstücksspeck which are smoked pork slices. Traditional German cold cuts favor ham over bacon, however "Wammerl" remains popular in Bavaria. Small bacon cubes have been a rather important ingredient of various southern German dishes, they are used for adding flavor to soups and salads and for speck dumplings and various noodle and potato dishes. Instead of preparing them at home from larger slices, they have been sold ready made as convenience foods as "B
Grilling is a form of cooking that involves dry heat applied to the surface of food from above or below. Grilling involves a significant amount of direct, radiant heat, tends to be used for cooking meat and vegetables quickly. Food to be grilled is cooked on a grill pan, or griddle. Heat transfer to the food when using a grill is through thermal radiation. Heat transfer when using a grill griddle is by direct conduction. In the United States, when the heat source for grilling comes from above, grilling is called broiling. In this case, the pan that holds the food is called a broiler pan, heat transfer is through thermal radiation. Direct heat grilling can expose food to temperatures in excess of 260 °C. Grilled meat acquires a distinctive roast aroma and flavor from a chemical process called the Maillard reaction; the Maillard reaction only occurs when foods reach temperatures in excess of 155 °C. Studies have shown that cooking beef, pork and fish at high temperatures can lead to the formation of heterocyclic amines and polycyclic aromatic hydrocarbons, which are carcinogens.
Marination may reduce the formation of these compounds. Grilling is presented as a healthy alternative to cooking with oils, although the fat and juices lost by grilling can contribute to drier food. In Japanese cities, yakitori carts, restaurants, or shops can be found; these marinated grilled meat on a stick. Yakiniku is a type of food where meat and/or vegetables are grilled directly over small charcoal or gas grills at high temperatures. In Malaysia, Singapore and Thailand, a popular food item from food vendors is satay, marinated meat on a bamboo skewer grilled over a charcoal fire and served with peanut sauce. In Germany, the most prominent outdoor form of grilling is using the gridiron over a bed of burning charcoal. Care is taken. Beer is sprinkled over the sausages or meat and used to suppress flames; the meat is marinated before grilling. Besides charcoal, sometimes gas and electric heat sources are used. Other methods are used less frequently. In Northern Mexico, carne asada is a staple food.
Popular cuts include arrachera and rib eye, as well as chorizo and chicken, among others. Charcoal, mesquite or firewood are used for the grilling. In Argentina and Uruguay, both asado and steak a la parrilla are staple dishes and hailed as national specialties. In Sweden, grilling directly over hot coals is the most prominent form of grilling; the meat is Boston butt, pork chops or pork fillet. It is common to cook meat and vegetables together on a skewer, this is called "grillspett". In the United Kingdom, Commonwealth countries, Ireland, grilling refers to cooking food directly under a source of direct, dry heat; the "grill" is a separate part of an oven where the food is inserted just under the element. This practice is referred to as "broiling" in North America. Sometimes the term grilling may refer to cooking with heat from below, as in the United States. In the 1970s and 1980s the electric, two sided vertical grill marketed by the Sunbeam company achieved cult status because of its quick, no added fat operation.
In electric ovens, grilling may be accomplished by placing the food near the upper heating element, with the lower heating element off and the oven door open. Grilling in an electric oven may create a large amount of smoke and cause splattering in the oven. Both gas and electric ovens have a separate compartment for grilling, such as a drawer below the flame or one of the stove top heating elements. In the United States, the use of the word grill refers to cooking food directly over a source of dry heat with the food sitting on a metal grate that leaves "grill marks." Grilling is done outdoors on charcoal grills or gas grills. Grilling may be performed using stove-top "grill pans" which have raised metal ridges for the food to sit on, or using an indoor electric grill. A skewer, brochette, or rotisserie may be used to cook small pieces of food; the resulting food product is called a "kabob" or "kebab" which means "to grill" in Persian. Kebab is short for "shish kebab". Mesquite or hickory wood chips may be added on top of the coals to create a smoldering effect that provides additional flavor to the food.
Other hardwoods such as pecan, apple and oak may be used. As is true of any high-temperature frying or baking, when meat is grilled at high temperatures, the cooking process can generate carcinogenic chemicals. Two processes are thought to be responsible. Heterocyclic amines are formed when amino acids and creatine react at high temperatures. Polycyclic aromatic hydrocarbons are formed when fat and juices from meat grilled directly over an open fire drip onto the fire, causing flames; these flames contain PAHs that adhere to the surface of the meat. However it is possible to reduce carcinogens when grilling meat, or mitigate their effect. Garlic, olive oil and vitamin E have been shown to reduce formation of both HCAs and PAHs. V-profiled grill elements placed at an angle may help drain much of the meat juices and dripping fat, transport them away from the heat source. Hea
Dried and salted cod
Dried and salted cod, sometimes referred to as salt cod, is cod, preserved by drying after salting. Cod, dried without the addition of salt is stockfish. Salt cod was long a major export of the North Atlantic region, has become an ingredient of many cuisines around the Atlantic and in the Mediterranean. With the sharp decline in the world stocks of cod, other salted and dried white fish are sometimes marketed as "salt cod", the term has become to some extent a generic name. Dried and salted cod has been produced for over 500 years in Newfoundland and the Faroe Islands, most in Norway where it is called klippfisk "cliff-fish". Traditionally it was dried outdoors by the wind and sun on cliffs and other bare rock-faces. Today klippfisk is dried indoors with the aid of electric heaters; the production of salt cod dates back at least 500 years, to the time of the European discoveries of the Grand Banks off Newfoundland. When explorer Jacques Cartier discovered the mouth of the St. Lawrence River in what is now Canada and claimed it for France, he noted the presence of a thousand Basque boats fishing for cod.
Salt cod formed a vital item of international commerce between the New World and the Old, formed one leg of the so-called triangular trade. Thus it spread around the Atlantic and became a traditional ingredient not only in Northern European cuisine, but in Mediterranean, West African and Brazilian cuisines; the drying of food is the world's oldest known preservation method, dried fish has a storage life of several years. Traditionally, salt cod was dried only by the wind and the sun, hanging on wooden scaffolding or lying on clean cliffs or rocks near the seaside. Drying preserves many nutrients, the process of salting and drying codfish is said to make it tastier. Salting became economically feasible during the 17th century, when cheap salt from southern Europe became available to the maritime nations of northern Europe; the method was cheap and the work could be done by the fisherman or his family. The resulting product was transported to market, salt cod became a staple item in the diet of the populations of Catholic countries on'meatless' Fridays and during Lent.
In Middle English salted cod was called haberdine. Dried cod and the dishes made from it are known by many names around the world, many of them derived from the root bacal-, itself of unknown origin. Explorer John Cabot reported; some of these are: bacalhau, bacalao salado, bacallà salat i assecat or bacallà salat, μπακαλιάρος, bakaliáros, cabillaud, baccalà, bakkeljauw, kapakala. Other names include ráktoguolli/goikeguolli, klipfisk/klippfisk/clipfish, stokvis/klipvis, morue, bakaljaw, "labardan"; the fish is beheaded and eviscerated on board the boat or ship. It is salted and dried ashore. Traditionally the fish was sun-dried on rocks or wooden frames, but modern commercial production is dried indoors with electrical heating, it is sold whole or in portions, without bones. Prior to the collapse of the Grand Banks stocks due to overfishing, salt cod was derived from Atlantic cod. Since products sold as salt cod may be derived from other whitefish, such as pollock, blue whiting and tusk. In Norway, there used to be five different grades of salt cod.
The best grade was called superior extra. Came superior, imperial and popular; these appellations are no longer extensively used, although some producers still make the superior products. The best klippfisk, the superior extra, is made only from line-caught cod; the fish is always of the cod that once a year is caught during spawning. The fish is bled while alive, it is cleaned and salted. Fishers and connoisseurs alike place a high importance in the fact that the fish is line-caught, because if caught in a net, the fish may be dead before caught, which may result in bruising of the fillets. For the same reason it is believed to be important. Superior klippfisk is salted fresh. Lower grades are salted by injecting a salt-water solution into the fish, while superior grades are salted with dry salt; the superior extra is dried twice, much like Parma ham. Between the two drying sessions, the fish rests and the flavour matures. Before it can be eaten, salt cod must be rehydrated and desalinated by soaking in cold water for one to three days, changing the water two to three times a day.
In Europe, the fish is prepared for the table in a wide variety of ways. In France, brandade de morue is a popular baked gratin dish of potatoes mashed with rehydrated salted cod, seasoned with garlic and olive oil; some Southern France recipes skip the potatoes altogether and blend the salted cod with seasonings into a paste. There is a wide variety of salt cod dishes in Portuguese cuisine. In Greece, fried cod is served with skordalia. Salt cod is part of many European celebrations of the Christmas Vigil, in particular the southern Italian Feast of the Seven Fishes. In several islands of the West Indies, it forms the basis of the common
Bacteria are a type of biological cell. They constitute a large domain of prokaryotic microorganisms. A few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, are present in most of its habitats. Bacteria inhabit soil, acidic hot springs, radioactive waste, the deep portions of Earth's crust. Bacteria live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, only about half of the bacterial phyla have species that can be grown in the laboratory; the study of bacteria is known as a branch of microbiology. There are 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water. There are 5×1030 bacteria on Earth, forming a biomass which exceeds that of all plants and animals. Bacteria are vital in many stages of the nutrient cycle by recycling nutrients such as the fixation of nitrogen from the atmosphere.
The nutrient cycle includes the decomposition of dead bodies. In the biological communities surrounding hydrothermal vents and cold seeps, extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane, to energy. Data reported by researchers in October 2012 and published in March 2013 suggested that bacteria thrive in the Mariana Trench, with a depth of up to 11 kilometres, is the deepest known part of the oceans. Other researchers reported related studies that microbes thrive inside rocks up to 580 metres below the sea floor under 2.6 kilometres of ocean off the coast of the northwestern United States. According to one of the researchers, "You can find microbes everywhere—they're adaptable to conditions, survive wherever they are."The famous notion that bacterial cells in the human body outnumber human cells by a factor of 10:1 has been debunked. There are 39 trillion bacterial cells in the human microbiota as personified by a "reference" 70 kg male 170 cm tall, whereas there are 30 trillion human cells in the body.
This means that although they do have the upper hand in actual numbers, it is only by 30%, not 900%. The largest number exist in the gut flora, a large number on the skin; the vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, though many are beneficial in the gut flora. However several species of bacteria are pathogenic and cause infectious diseases, including cholera, anthrax and bubonic plague; the most common fatal bacterial diseases are respiratory infections, with tuberculosis alone killing about 2 million people per year in sub-Saharan Africa. In developed countries, antibiotics are used to treat bacterial infections and are used in farming, making antibiotic resistance a growing problem. In industry, bacteria are important in sewage treatment and the breakdown of oil spills, the production of cheese and yogurt through fermentation, the recovery of gold, palladium and other metals in the mining sector, as well as in biotechnology, the manufacture of antibiotics and other chemicals.
Once regarded as plants constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and harbour membrane-bound organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two different groups of organisms that evolved from an ancient common ancestor; these evolutionary domains are called Archaea. The word bacteria is the plural of the New Latin bacterium, the latinisation of the Greek βακτήριον, the diminutive of βακτηρία, meaning "staff, cane", because the first ones to be discovered were rod-shaped; the ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, about 4 billion years ago. For about 3 billion years, most organisms were microscopic, bacteria and archaea were the dominant forms of life. Although bacterial fossils exist, such as stromatolites, their lack of distinctive morphology prevents them from being used to examine the history of bacterial evolution, or to date the time of origin of a particular bacterial species.
However, gene sequences can be used to reconstruct the bacterial phylogeny, these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage. The most recent common ancestor of bacteria and archaea was a hyperthermophile that lived about 2.5 billion–3.2 billion years ago. Bacteria were involved in the second great evolutionary divergence, that of the archaea and eukaryotes. Here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves related to the Archaea; this involved the engulfment by proto-eukaryotic cells of alphaproteobacterial symbionts to form either mitochondria or hydrogenosomes, which are still found in all known Eukarya. Some eukaryotes that contained mitochondria engulfed cyanobacteria-like organisms, leading to the formation of chloroplasts in algae and plants; this is known as primary endosymbiosis. Bacteria display a wide diversity of sizes, called morphologies.
Bacterial cells are about one-tenth the size of eukaryotic cells