A sugar is a form of carbohydrate; the most commonly used sugar is a white crystalline solid, sucrose; used to alter the flavor of beverages and food. The "simple" sugars, such as glucose (which exists within sucrose), store potential energy which is used by biological cells.
In culinary terms, sugar is a type of food associated with one of the primary taste sensations, that of sweetness. Culinary sugar is available in many forms, from "brown" or "raw" (which is not truly raw, but refined from sugarcane) to highly refined "white" sugar. Turbinado sugar is raw sugar that has been steam-cleaned. Sugar comes in lumps, grains, powder, cubes, octogons, and fruity loops.
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The major cane sugar producing countries are countries with warm climates, such as Australia, Brazil, and Thailand. In 2001/2002 there was over twice as much sugar produced in developing countries as in developed countries. The greatest quantity of sugar is produced in Latin America and the Caribbean nations, and in the Far East.
Ironically, the world's second largest sugar exporter is the EU. Although beet sugar costs four times as much to produce as cane sugar, huge subsidies and a high import tariff make it difficult for other countries to export to the EU, or compete with it on world markets. The U.S. sets high sugar prices to support its producers with the effect that many sugar consumers have switched to corn syrup (beverage manufacturers) or moved out of the country (candy makers).
The raw vegetable material is crushed, and the juice is collected and filtered. The liquid is then treated (often with lime) to remove impurities, this is then neutralised with sulfur dioxide. The juice is then boiled, sediment settles to the bottom and can be dredged out, scum rises to the surface and this is skimmed off. The heat is removed and the liquid crystallises, usually while being stirred, to produce sugar which can be poured into moulds. A centrifuge can also be used during crystallisation.
There is little difference between sugar made from beet and that made from cane, but sophisticated tests can distinguish the two, and have been developed to reduce fraudulent abuse of EU subsidies.
In biochemistry, a sugar is the simplest molecule that can be identified as a carbohydrate. These are monosaccharides and disaccharides. Sugars contain either aldehyde groups (-CHO) or ketone groups (C=O), where there are carbon-oxygen double bonds, making the sugars reactive. Most sugars conform to (CH2O)n where n is between 3 and 7. A notable exception is deoxyribose, which as the name suggests is "missing" an oxygen. As well as being clasified by their reactive group, sugars are also classified by the number of carbons they contain. Derivatives of trioses (C3H6O3) are intermediates in glycolysis. Pentoses include ribose and deoxyribose, which are present in nucleic acids. Ribose is also a component of several chemicals that are important to the metabolic process, including NADH and ATP. Hexoses include glucose which is a universal substrate for the production of energy in the form of ATP. During photosynthesis plants produce glucose which is then stored as starch.
Many pentoses and hexoses are capable of forming ring structures. In these closed-chain forms the aldehyde or ketone group is not free, so many of the reactions typical of these groups cannot occur. Glucose in solution exists mostly as a ring at equilibrium, with less than 0.1% of the molecules in the open-chain form.
Monosaccharides in a closed-chain form can form glycosidic bonds with other monosaccharides, creating disaccharides, such as sucrose, and polysaccharides such as starch. Glycosidic bonds must be hydrolised or otherwise broken by enzymes before such compounds can be used in metabolism.
The term "glyco-" indicates the presence of a sugar in an otherwise non-carbohydrate substance: for example, a glycoprotein is a protein to which one or more sugars are connected.
Sucrose can be converted by hydrolysis into fructose and glucose, producing what is called inverted sugar. This resulting sugar is sweeter than the original sucrose, and is useful for making confections sweeter and softer in texture.
Sugar cane has long been known in tropical areas of the world, and was chewed raw to extract its sweetness.
Later sugar refining was developed in the Middle East, India and China, where it became a staple of cooking and desserts.
Later sugar spread to other areas of the world through trade.
It arrived in Europe with the arrival of the Moors.
Crusaders also brought sugar home with them after their campaigns in the Holy Land.
While sugar cane could not be grown in Europe, sugar beets could and these began to be widely cultivated.
With the European colonization of the new world the Caribbean became the world's largest source of sugar. Sugar cane could be grown on these islands using slave labour at vastly lower prices than sugar beets could be grown in Europe, or cane sugar imported from the East. Thus the economies of entire islands such as Tobago, Guadaloupe, and Barbados were based on sugar production. Sugar prices fell, especially in Britain, and what had previously been a luxury good began, by the eighteenth century, to be commonly consumed by all levels of society. At first most sugar in Britain was used in tea, but later candies and chocolates became extremely popular. Sugar was commonly sold in solid cones and required a sugar nip, a plyers-like tool, to break off pieces.
Sugar cane quickly exhausts the soil and production soon fell dramatically in the Caribbean. Production thus spread to South America as well as to new European colonies in Africa. While it is no longer grown by slaves, sugar growing continues to this day to be associated with workers earning minimal wages and living in extreme poverty. Cuba was a large producer of sugar in the 20th century until the collapse of the Soviet Union took away their export market and the industry collapsed.