Sugarcane
|
? Sugarcane |
|||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
 Sugar cane
leaves
|
|||||||||||||
| Scientific classification | |||||||||||||
|
|||||||||||||
|
Species
|
|||||||||||||
| Saccharum
arundinaceum Saccharum bengalense Saccharum edule Saccharum officinarum Saccharum procerum Saccharum ravennae Saccharum robustum Saccharum sinense Saccharum spontaneum |
Sugarcane or Sugar cane (Saccharum) is a genus of between 6 and 37 species (depending on taxonomic interpretation) of tall grasses (family Poaceae, tribe Andropogoneae), native to warm temperate to tropical regions of the Old World. They have stout, jointed fibrous stalks 2 m – 6 m tall and sap rich in sugar. All the species interbreed, and the major commercial cultivars are complex hybrids.
Cultivation and uses
About 107 countries grow the crop to produce 1,324 million tonnes (more than 6 times the amount of sugar beet produced). The largest producers are Brazil, India, and China, accounting for more than 50% of world production.
History
- For a longer history, see Sugar.
Sugar Cane is a type of grass originally from southeast Asia. The thick stalk stores energy as sucrose in the sap. From this juice sugar is extracted by evaporating the water. Crystalized sugar was reported 2500 years ago in China and India. Around the eighth century A.D. the Arabs introduced sugar to the Mediterranean and it was cultivated in Spain. It was among the early crops brought to the Americas by Spaniards.
Sugar cane was grown extensively in the Caribbean and still is on some islands. In colonial times sugar was a major product of the triangular trade of New World raw materials, European manufactures and African slaves. France found its sugar cane islands so valuable it effectively traded Canada to Britain for their return of Guadeloupe, Martinique and St. Lucia at the end of the Seven Years' War. The Dutch similarly kept Suriname, a sugar colony in South America, instead of seeking the return of the New Netherlands (New Amsterdam). Cuban sugar cane produced sugar which received price supports from and a guaranteed market in the USSR; the dissolution of that country forced the closure of most of Cuba's sugar industry. Sugar cane is still an important part of the economy in Barbados, the Dominican Republic, Guadeloupe, Jamaica, Grenada, and other islands. The sugar cane industry is a major export for the Caribbean, but it is expected to collapse with the removal of European preferences by 2009.
 Sugar cane
Saccharum
officinarum at Kew Gardens,
London
|
 Saccharum
officinarum grown in
Hawaii
|
Sugar cane production also greatly influenced the modern history of many tropical Pacific islands, most particularly the Hawaii and Fiji. In these islands, sugar came to dominate the economic and political landscape after the indigenous societies were invaded by Europeans and Americans. The Europeans and Americans also promoted immigration from various Asian countries for workers to tend and harvest the crop. Sugar-industry policies eventually established the ethnic makeup of the island populations that now exist, profoundly affecting modern politics and society in the islands.
Brazil is a major grower of sugar cane, where it is used to produce sugar as well as to provide the alcohol used in making gasohol and biodiesel fuels.
Cultivation
Sugarcane cultivation requires a tropical or subtropical climate, with a minimum of 600 mm (24 in) of annual moisture. It is one of the most efficient photosynthsizers in the plant kingdom, able to convert up to 2% of incident solar energy into biomass. In prime growing regions, such as Hawaii, sugarcane can produce 20 kg for each square metre exposed to the sun.
Sugarcane is propagated from cuttings rather than from seed. Each cutting must contain at least one bud, and the cuttings are usually planted by hand. Once planted, a stand of cane can be harvested several times; after each harvest, the cane sends up new stalks, called ratoons. Usually, each successive harvest gives a smaller yield, and eventually the declining yields justify replanting. Depending on agricultural practice, 2 to 10 harvests may be possible between each planting.
Sugar cane is used as a food plant by the larvae of some lepidoptera species, including turnip moth.
Sugar cane is harvested by hand or mechanically. Hand harvesting accounts for more than half of the world's production, and is especially dominant in the developing world. When harvested by hand, the field is first set on fire. The fire spreads very rapidly, burning away the leaves, but leaving the water-rich stalks and roots unharmed. Harvesters then cut the standing cane just above the ground with knives. A skilled cane harvester can cut 500 kg of sugar cane in an hour.
The sugar cane combine, or chopper harvester, is a harvesting machine originally developed in Australia. The combine cuts the cane at the base of the stalk, separates the cane from its leaves, and then deposits the cane into a cart while blowing the cut leaves back onto the field. Such machines can harvest 30 tonnes of cane each hour, but cane harvested using these machines must be transported to the processing plant rapidly; once cut, sugar cane begins to lose its sugar content, and damage inflicted on the cane during mechanical harvesting only accelerates this decay.
Processing
Traditionally, sugarcane has been processed in two stages. Sugar cane mills, located in sugarcane producing regions, extract sugar from freshly harvested sugarcane, resulting in raw sugar for later refining, and in mill white sugar for local consumption. Sugar refineries, often located in heavy sugar-consuming regions such as North America, Europe, and Japan, then purify raw sugar to produce refined white sugar, a product that is more than 99% pure sucrose. These two stages are, however, slowly becoming blurred. Increasing affluence in the sugar-producing tropics has led to an increase in demand for refined sugar products in those areas, and there is a trend towards combined milling and refining in these areas.
Milling
In a sugar mill, sugarcane is washed, and then chopped and shredded by revolving knives. The shredded cane is then repeatedly mixed with water and crushed between rollers; the collected juices (called garapa in Brazil) contain 10–15% sucrose, while the remaining fibrous solids, called bagasse, are burnt for fuel. Bagasse makes a sugar mill more than self-sufficient in energy; the surplus bagasse can be used for animal feed, in paper manufacture, or burnt to generate electricity for the local power grid.
The cane juice is next mixed with lime to adjust its pH to 7. This arrests sucrose's decay into glucose and fructose, and precipitates out some impurities. The mixture then sits, allowing the lime and other suspended solids to settle out, and the clarified juice is then concentrated in a multiple-effect evaporator to make a syrup about 60% by weight in sucrose. This syrup is further concentrated under vacuum until it becomes supersaturated, and then seeded with crystalline sugar. Upon cooling, sugar crystallizes out of the syrup. A centrifuge is used to separate the sugar from the remaining liquid, or molasses. Additional crystallizations may be performed to extract more sugar from the molasses; the molasses remaining after no more sugar can be extracted from it in a cost-effective fashion is called blackstrap.
Raw sugar has a yellow to brown colour. If a white product is desired, sulfur dioxide may be bubbled through the cane juice prior to evaporation. This bleaches many colour-forming impurities into colorless ones. Sugar bleached white by this sulfitation process is called mill white, plantation white or crystal sugar. This form of sugar is the most commonly consumed form of sugar in sugarcane-producing countries.
Refining
In sugar refining, raw sugar is further purified. First, the raw sugar is mixed with heavy syrup and then centrifuged clean. This process is called affination; its purpose is to wash away the outer coating of the raw sugar crystals, which is less pure than the crystal interior. The remaining sugar is then dissolved to make a syrup, about 70% by weight solids.
The sugar solution is then clarified by the addition of phosphoric acid and calcium hydroxide, which combine to precipitate calcium phosphate. The calcium phosphate particles entrap some impurities and adsorb others, and then float to the top of the tank where they can be skimmed off. An alternative to this phosphatation technique is carbonatation, which is similar, but uses carbon dioxide and calcium hydroxide to produce a calcium carbonate precipitate.
After any remaining solids are filtered out, the clarified syrup is decolorized by filtration through a bed of activated carbon ( bone char was traditionally used in this role, but its use is no longer common). Some remaining colour-forming impurities adsorb to the carbon bed. The purified syrup is then concentrated to supersaturation and repeatedly crystallized under vacuum, to produce white refined sugar. As in a sugar mill, the sugar crystals are separated from the molasses by centrifugation. Additional sugar is recovered by blending the remaining syrup with the washings from affination and again crystallizing to produce brown sugar. When no more sugar can be economically recovered, the final molasses still contains 20–30% sucrose, as well as 15–25% glucose and fructose.
To produce granulated sugar in which the individual sugar grains do not clump together, sugar must be dried. This is accomplished first by drying the sugar in a hot rotary dryer, and then by conditioning the sugar by blowing cool air through it for several days.
Ribbon cane syrup
Ribbon cane is a subtropical type that was once widely grown in southern United States, as far north as coastal North Carolina. The juice was extracted with horse or mule-powered crushers, then the juice was boiled, similar to maple syrup, in a flat pan, then used in the syrup form as a sweetener for other foods. It is not a commercial crop nowadays, but a few growers try to keep alive the old traditions and find ready sales for their product. Most sugar cane production in the United States occurs in Florida and Louisiana, and to a lesser extent in Hawaii and Texas.
Sugarcane as foodstuff
In most countries where sugarcane is cultivated, there are several foodstuffs and popular dishes derived from it, such as:
- Direct consumption of raw sugarcane cylinders or cubes, which are chewed to extract the juice and the bagasse is spit out
- Freshly extracted juice ( garapa, guarab, guarapa or caldo de cana) by hand- or electrically operated small mills, with a touch of lemon and ice, makes a delicious and very popular drink.
- Molasses, used as a sweetener and also as a syrup accompanying other foods, such as cheese
- Rapadura, a candy made of flavoured solid brown sugar in Brazil, which can be consumed in small hard blocks, or in pulverized form (flour), as an add-on to other desserts.