In chemistry, a dehydration reaction is a conversion that involves the loss of water from the reacting molecule or ion. Dehydration reactions are the reverse of a hydration reaction. Common dehydrating agents used in organic synthesis include sulfuric alumina. Dehydration reactions are effected with heating; the classic example of a dehydration reaction is the Fischer esterification, which involves treating a carboxylic acid with an alcohol in the presence of a dehydrating agent: RCO2H + R′OH ⇌ RCO2R′ + H2OTwo monosaccharides, such as glucose and fructose, can be joined together using dehydration synthesis. The new molecule, consisting of two monosaccharides, is called a disaccharide; the process of hydrolysis is the reverse reaction, meaning that the water is recombined with the two hydroxyl groups and the disaccharide reverts to being monosaccharides. In the related condensation reaction water is released from two different reactants. In organic synthesis, there are many examples of dehydration reaction, for example dehydration of alcohols or sugars.
Other examples of dehydration synthesis reactions are the formation of triglycerides from fatty acids and the formation of glycosidic bonds between carbohydrate molecules, such as the formation of maltose from two glucose molecules. Hydration reaction
In chemistry, pH is a scale used to specify how acidic or basic a water-based solution is. Acidic solutions have a lower pH, while basic solutions have a higher pH. At room temperature, pure water is neither acidic nor basic and has a pH of 7; the pH scale is logarithmic and approximates the negative of the base 10 logarithm of the molar concentration of hydrogen ions in a solution. More it is the negative of the base 10 logarithm of the activity of the hydrogen ion. At 25 °C, solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic; the neutral value of the pH depends on the temperature, being lower than 7 if the temperature increases. Contrary to popular belief, the pH value can be less than 0 or greater than 14 for strong acids and bases respectively; the pH scale is traceable to a set of standard solutions whose pH is established by international agreement. Primary pH standard values are determined using a concentration cell with transference, by measuring the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode.
The pH of aqueous solutions can be measured with a glass electrode and a pH meter, or a color-changing indicator. Measurements of pH are important in chemistry, medicine, water treatment, many other applications; the concept of pH was first introduced by the Danish chemist Søren Peder Lauritz Sørensen at the Carlsberg Laboratory in 1909 and revised to the modern pH in 1924 to accommodate definitions and measurements in terms of electrochemical cells. In the first papers, the notation had the "H" as a subscript to the lowercase "p", as so: pH; the exact meaning of the "p" in "pH" is disputed, but according to the Carlsberg Foundation, pH stands for "power of hydrogen". It has been suggested that the "p" stands for the German Potenz, others refer to French puissance. Another suggestion is that the "p" stands for the Latin terms pondus hydrogenii, potentia hydrogenii, or potential hydrogen, it is suggested that Sørensen used the letters "p" and "q" to label the test solution and the reference solution.
In chemistry, the p stands for "decimal cologarithm of", is used in the term pKa, used for acid dissociation constants. Bacteriologist Alice C. Evans, famed for her work's influence on dairying and food safety, credited William Mansfield Clark and colleagues with developing pH measuring methods in the 1910s, which had a wide influence on laboratory and industrial use thereafter. In her memoir, she does not mention how much, or how little and colleagues knew about Sørensen's work a few years prior, she said: In these studies Dr. Clark's attention was directed to the effect of acid on the growth of bacteria, he found that it is the intensity of the acid in terms of hydrogen-ion concentration that affects their growth. But existing methods of measuring acidity determined not the intensity, of the acid. Next, with his collaborators, Dr. Clark developed accurate methods for measuring hydrogen-ion concentration; these methods replaced the inaccurate titration method of determining acid content in use in biologic laboratories throughout the world.
They were found to be applicable in many industrial and other processes in which they came into wide usage. The first electronic method for measuring pH was invented by Arnold Orville Beckman, a professor at California Institute of Technology in 1934, it was in response to local citrus grower Sunkist that wanted a better method for testing the pH of lemons they were picking from their nearby orchards. PH is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity, aH+, in a solution. PH = − log 10 = log 10 For example, for a solution with a hydrogen ion activity of 5×10−6 we get 1/ = 2×105, thus such a solution has a pH of log10 = 5.3. For a commonplace example based on the facts that the masses of a mole of water, a mole of hydrogen ions, a mole of hydroxide ions are 18 g, 1 g, 17 g, a quantity of 107 moles of pure water, or 180 tonnes, contains close to 1 g of dissociated hydrogen ions and 17 g of hydroxide ions. Note that pH depends on temperature. For instance at 0 °C the pH of pure water is 7.47.
At 25 °C it's 7.00, at 100 °C it's 6.14. This definition was adopted because ion-selective electrodes, which are used to measure pH, respond to activity. Ideally, electrode potential, E, follows the Nernst equation, for the hydrogen ion can be written as E = E 0 + R T F ln = E 0 − 2.303 R T F pH where E is a measured potential, E0 is the standard electrode potential, R is the gas const
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
French onion soup
French onion soup is a type of soup based on meat stock and onions, served gratinéed with croutons and cheese on top or a large piece of bread. Although ancient in origin, the dish underwent a resurgence of popularity in the 1960s in the United States due to a greater interest in French cuisine. French onion soup is served as a starter. Onion soups have been popular at least as far back as Roman times. Throughout history, they were seen as food for poor people, as onions were plentiful and easy to grow; the modern version of this soup originates in Paris, France in the 18th century, made from beef broth, caramelized onions. It is finished by being placed under a grill in a ramekin with croutons and Comté melted on top; the crouton on top is reminiscent of ancient soups. Recipes for onion soup vary greatly: Though the liquid is meat stock, it may be water. Milk may be added, it may be thickened with eggs or flour. It may be gratinéed or not. Recipes specify that the onions should be cooked becoming caramelized.
Brandy or sherry is added at the end. The soup base is topped with a slice of bread. For the gratinéed version, the croute is topped with cheese and baked; the soup is immediately served in the bowl or ramekin in which it was broiled, baked, or—in family-style—immediately transferred to individual serving bowls via a ladle. Some alternative names for the soup include: Soupe à l'oignon à la Parisienne Gratinée Parisienne Gratinée des Halles Gratinée Lyonnaise Soupe à l'oignon Lyonnaise Soupe à l'oignon Gratinée French cuisine French onion dip List of French soups and stews List of onion dishes List of soups List of vegetable soups Onion sauce Sop Vegetable soup Onion Soup at Wikibook Cookbooks
A mirepoix is a flavour base made from diced vegetables that are cooked with butter, oil, or other fat, for a long time on a low heat without colour or browning. It is not sautéed or otherwise hard cooked because the intention is to sweeten the ingredients rather than caramelise them, it is a long-standing cooking technique in French cuisine. Further cooking with the addition of tomato purée, creates a darkened brown mixture called pincage; when the mirepoix is not precooked, the constituent vegetables may be cut to a larger size, depending on the overall cooking time for the dish. The vegetable mixture is onions and celery, with the traditional ratio being 2:1:1, two parts onion, one part carrot, one part celery. Mirepoix is the flavour base for a wide variety of Western dishes: stocks, soups and sauces. Similar flavour bases include the Italian soffritto, the Spanish sofrito, refogado/sufrito from Portuguese-speaking nations, the German Suppengrün, the Polish włoszczyzna, the Russian/Ukrainian smazhennya or zazharka, the US Cajun / Creole holy trinity, the French duxelles.
Though the cooking technique is older, the word mirepoix dates from the 18th century and derives, as do many other appellations in French cuisine, from the aristocratic employer of the cook credited with establishing and stabilizing it: in this case, Charles-Pierre-Gaston François de Lévis, duc de Lévis-Mirepoix, French field marshal and ambassador and a member of the noble family of Lévis, lords of Mirepoix, Ariège, in Languedoc since the 11th century. According to Pierre Larousse, the unfortunate Duke of Mirepoix was "an incompetent and mediocre individual... who owed his vast fortune to the affection Louis XV felt toward his wife and who had but one claim to fame: he gave his name to a sauce made of all kinds of meat and a variety of seasonings". The term is not encountered in French culinary texts until the 19th century, so it is difficult to know what a dish à la mirepoix was like in 18th-century France. Antoine Beauvilliers, for instance, in 1814, gives a short recipe for a Sauce à la Mirepoix, a buttery, wine-laced stock garnished with an aromatic mixture of carrots, a bouquet garni.
Marie-Antoine Carême, in the 1830s, gives a similar recipe, calling it "Mire-poix". By the mid-19th century, Jules Gouffé refers to a mirepoix as "a term in use for such a long time that I do not hesitate to use it here", his mirepoix is listed among essences and, indeed, is a meaty concoction, like all other essences, was used to enrich many a classic sauce. By the end of the 19th century, the mirepoix had taken on its modern meaning. Joseph Favre, in his Dictionnaire universel de cuisine, uses the term to describe a mixture of ham, carrots and herbs used as an aromatic condiment when making sauces or braising meat; the matignon is similar to the mirepoix, except that the matignon is designed to be brought to the table and eaten with the dish or alone as a side dish. According to the 1938 Larousse Gastronomique, a mirepoix may be prepared "au gras" or "au maigre". Mirepoix au maigre is sometimes called a brunoise. A mirepoix au gras contains diced pork belly as an additional ingredient. Similar combinations, both in and out of the French culinary repertoire, may include leeks, garlic, shallots, bell peppers and ginger, according to the requirements of the regional cuisine or the instructions of the particular chef or recipe.
The analogous soffritto is the basis for many traditional dishes in classic Italian cuisine, the sofrito serves a similar purpose in Spanish cuisines. In Cajun and Creole cuisine, a mirepoix or "holy trinity" is a combination of onions and bell peppers. Traditionally, the weight ratio for mirepoix is 2:1:1 of onions and carrots; when making a white stock, or fond blanc, parsnips are used instead of carrots to maintain the pale color. Suppengrün means soup greens in German, the Dutch equivalent is soepgroente. Soup greens come in a bundle and consists of a leek, a carrot, a piece of celeriac, it may contain parsley, celery leaves, parsley root, onions. The mix depends on regional traditions, as well as individual recipes; the vegetables used are cold-climate bulbs with long shelf lives. Suppengrün act as herbs and impart hearty, strong flavors to the soup or sauce, providing a foil for other strong tasting ingredients such as dried peas and beans or pot roast. Large chunks of vegetables are slow cooked to make flavorful soups and stocks, are discarded when the vegetables have given up most of their flavor.
Finely chopped suppengrün are used as a basis for a finished sauce. The vegetables may be cooked long enough until they fall apart, may become part of the sauce or pureed to form the sauce. In Italian cuisine, chopped onions and celery is battuto, slowly cooked in olive oil, becomes soffritto, it is used as the base for most pasta sauces, such as arrabbiata sauc
Sucrose is common sugar. It is a molecule composed of two monosaccharides: glucose and fructose. Sucrose is produced in plants, from which table sugar is refined, it has the molecular formula C12H22O11. For human consumption, sucrose is extracted, refined, from either sugar cane or sugar beet. Sugar mills are located where sugarcane is grown to crush the cane and produce raw sugar, shipped around the world for refining into pure sucrose; some sugar mills process the raw sugar into pure sucrose. Sugar beet factories are located in colder climates where the beet is grown and process the beets directly into refined sugar; the sugar refining process involves washing the raw sugar crystals before dissolving them into a sugar syrup, filtered and passed over carbon to remove any residual colour. The by-now clear sugar syrup is concentrated by boiling under a vacuum and crystallized as the final purification process to produce crystals of pure sucrose; these crystals are clear and have a sweet taste. En masse, the crystals appear white.
Sugar is an added ingredient in food production and food recipes. About 185 million tonnes of sugar were produced worldwide in 2017; the word sucrose was coined in 1857 by the English chemist William Miller from the French sucre and the generic chemical suffix for sugars -ose. The abbreviated term Suc is used for sucrose in scientific literature; the name saccharose was coined in 1860 by the French chemist Marcellin Berthelot. Saccharose is an obsolete name for sugars in general sucrose. In sucrose, the components glucose and fructose are linked via an ether bond between C1 on the glucosyl subunit and C2 on the fructosyl unit; the bond is called a glycosidic linkage. Glucose exists predominantly as two isomeric "pyranoses", but only one of these forms links to the fructose. Fructose itself exists as a mixture of "furanoses", each of which having α and β isomers, but only one particular isomer links to the glucosyl unit. What is notable about sucrose is that, unlike most disaccharides, the glycosidic bond is formed between the reducing ends of both glucose and fructose, not between the reducing end of one and the nonreducing end of the other.
This linkage inhibits further bonding to other saccharide units. Since it contains no anomeric hydroxyl groups, it is classified as a non-reducing sugar. Sucrose crystallizes in the monoclinic space group P21 with room-temperature lattice parameters a = 1.08631 nm, b = 0.87044 nm, c = 0.77624 nm, β = 102.938°. The purity of sucrose is measured by polarimetry, through the rotation of plane-polarized light by a solution of sugar; the specific rotation at 20 °C using yellow "sodium-D" light is +66.47°. Commercial samples of sugar are assayed using this parameter. Sucrose does not deteriorate at ambient conditions. Sucrose does not melt at high temperatures. Instead, it decomposes at 186 °C to form caramel. Like other carbohydrates, it combusts to carbon water. Mixing sucrose with the oxidizer potassium nitrate produces the fuel known as rocket candy, used to propel amateur rocket motors. C12H22O11 + 6 KNO3 → 9 CO + 3 N2 + 11 H2O + 3 K2CO3This reaction is somewhat simplified though; some of the carbon does get oxidized to carbon dioxide, other reactions, such as the water-gas shift reaction take place.
A more accurate theoretical equation is: C12H22O11 + 6.288 KNO3 → 3.796 CO2 + 5.205 CO + 7.794 H2O + 3.065 H2 + 3.143 N2 + 2.998 K2CO3 + 0.274 KOH Sucrose burns with chloric acid, formed by the reaction of hydrochloric acid and potassium chlorate: 8 HClO3 + C12H22O11 → 11 H2O + 12 CO2 + 8 HClSucrose can be dehydrated with sulfuric acid to form a black, carbon-rich solid, as indicated in the following idealized equation: H2SO4 + C12H22O11 → 12 C + 11 H2O + Heat. The formula for sucrose's decomposition can be represented as a two-step reaction: the first simplified reaction is dehydration of sucrose to pure carbon and water, carbon oxidises to CO2 with O2 from air. C12H22O11 + heat → 12 C + 11 H2O 12 C + 12 O2 → 12 CO2 Hydrolysis breaks the glycosidic bond converting sucrose into glucose and fructose. Hydrolysis is, however, so slow. If the enzyme sucrase is added, the reaction will proceed rapidly. Hydrolysis can be accelerated with acids, such as cream of tartar or lemon juice, both weak acids.
Gastric acidity converts sucrose to glucose and fructose during digestion, the bond between them being an acetal bond which can be broken by an acid. Given heats of combustion of 1349.6 kcal/mol for sucrose, 673.0 for glucose, 675.6 for fructose, hydrolysis releases about 1.0 kcal per mole of sucrose, or about 3 small calories per gram of product. The biosynthesis of sucrose proceeds via the precursors UDP-glucose and fructose 6-phosphate, catalyzed by the enzyme sucrose-6-phosphate synthase; the energy for the reaction is gained by the cleavage of uridine diphosphate. Sucrose is formed by plants and cyanobacteria but not by other organisms. Sucrose is found in many food plants along with the monosaccharide fructose. In many fruits, such as pineapple and apricot, sucrose is the main sugar. In others, such as grapes and pears, fructose is the main sugar. Although sucrose is invariably isolated from natural sources, its chemical synthesis was first achieved in 1953 by Raymond Lemieux. In nature, sucrose is present in many plants, in particular their roots and nectars, because it serves as a way to store energy from photosynthesis.
Many mammals, birds and bacteria accumulate and feed on the sucrose in plants and for some it is their main food sou
Brown sugar is a sucrose sugar product with a distinctive brown color due to the presence of molasses. It is either an unrefined or refined soft sugar consisting of sugar crystals with some residual molasses content, or it is produced by the addition of molasses to refined white sugar; the Codex Alimentarius requires brown sugar to contain at least 88% of sucrose plus invert sugar. Commercial brown sugar contains from 3.5% molasses to 6.5% molasses based on total volume. Based on total weight, regular commercial brown sugar contains up to 10% molasses; the product is moist from the hygroscopic nature of the molasses and is labelled as "soft." The product may undergo processing to give a product. The addition of dyes or other chemicals may be permitted for industrial products. Particle size is variable but less than granulated white sugar. Products for industrial use may be based on caster sugar which has crystals of 0.35 mm. Brown sugar is produced by adding sugarcane molasses to refined white sugar crystals to more control the ratio of molasses to sugar crystals and to reduce manufacturing costs.
Brown sugar prepared in this manner is much coarser than its unrefined equivalent and its molasses may be separated from the crystals by washing to reveal the underlying white sugar crystals. The molasses used for food is obtained from sugar cane, because the flavor is preferred over beet sugar molasses, although in some areas in Belgium and the Netherlands, sugar beet molasses is used; the white sugar used can be from either beet or cane, as the chemical composition, nutritional value and taste of refined white sugar is for practical purposes the same, no matter from what plant it originates. With less-than-perfect refining, the small differences in color and taste of the white sugar will be masked by the molasses. In the late 19th century, the newly consolidated refined white sugar industry, which did not have full control over brown sugar production, mounted a smear campaign against brown sugar, reproducing microscopic photographs of harmless but repulsive-looking microbes living in brown sugar.
The effort was so successful that by 1900, a best-selling cookbook warned that brown sugar was of inferior quality and was susceptible to infestation by "a minute insect". This campaign of disinformation was felt in other sectors using raw or brown sugar such as brewing. For this reason, raw sugars must always be considered dangerous brewing materials. Natural brown sugar, raw sugar or whole cane sugar are sugars that retain a small to large amount of the molasses from the mother liquor. Based upon weight, brown cane sugar when refined yields up to 70% white sugar, the degree depending on how much molasses remained in the sugar crystals, which in turn is dependent upon whether the brown sugar was centrifuged or not; as there is more molasses in natural brown sugar, it contains minor nutritional value and mineral content. Some natural brown sugars have particular names and characteristics, are sold as turbinado, demerara or raw sugar if they have been centrifuged to a large degree. Brown sugars that have been only mildly centrifuged or unrefined retain a much higher degree of molasses and are called various names across the globe according to their country of origin: e.g. panela, jaggery, piloncillo, etc.
Although brown sugar has been touted as having health benefits ranging from soothing menstrual cramps to serving as an anti-aging skin treatment, there is no nutritional basis to support brown sugar as a healthier alternative to refined sugars despite the negligible amounts of minerals in brown sugar not found in white sugar. Turbinado, demerara and so-called "raw" sugars are made from crystallized evaporated sugar cane juice and spun in a centrifuge to remove all of the molasses; the sugar crystals are golden-coloured. This sugar can be sold as sent to the refinery to produce white sugar. Muscovado, piloncillo, chancaca and other natural dark brown sugars have been minimally centrifuged or not at all; these sugars are made in smaller factories or "cottage industries" in developing nations, where they are produced with traditional practices that do not make use of industrialized vacuum evaporators or centrifuges. They are boiled in open pans upon wood-fired stoves until the sugar cane juice reaches 30% of the former volume and sucrose crystallization begins.
They are poured into molds to solidify or onto cooling pans where they are beaten or worked vigorously to produce a granulated brown sugar. In some countries, such as Mauritius or the Philippines, a natural brown sugar called muscovado is produced by centrifuging the evaporated and crystallizing cane juice to create a sugar-crystal rich mush, allowed to drain under gravity to produce varying degrees of molasses content in the final product; this process approximates a modernized practice introduced in the 19th century to generate a better quality of natural brown sugar. A similar Japanese version of uncentrifuged natural cane sugar is called kokuto; this is a regional specialty