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Sugarcane or Sugar cane (Saccharum) is a genus of between 6–37 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 2–6 m tall and sap rich in sugar. All the species interbreed, and the major commercial cultivars are complex hybrids.

Cultivation and uses

Saccharum officinarum grown in HawaiiThere are 13 million hectares (32 million acres) of sugar cane plantations worldwide, with over 100 countries growing the crop. The top twenty producing countries harvested 1200 million metric tons of sugar cane in 2002 (more than 6 times the amount of sugar beet produced). The largest producers are Brazil, India, and China.

The history of sugar in the West is an important subject for understanding the emerging industrial power of Europe in the 1700s and 1800s. 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 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 a large 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 2008.

Sugar cane production also greatly influenced the modern history of many tropical Pacific islands, most particularly the Hawaiian Islands 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.

Sugarcane cultivation requires a tropical or subtropical climate, with a minimum of 60 cm (24 in) of annual moisture. It is one of the most efficient photosynthsizers in the plant kingdom, able to convert as much as 2% of incident solar energy into biomass. In prime growing regions, such as Hawaii, sugarcane harvests can exceed 200 metric tons per hectare.

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, 2–10 harvests may intervene between each planting.

Sugarcane is harvested either by hand or mechanically. Hand harvesting accounts for more than half of the world's sugarcane 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 sugarcane in an hour.

The sugarcane 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 metric tons of cane each hour, but cane harvested using them must be transported to the processing plant rapidly; once cut, sugarcane begins to lose its sugar content, and damage inflicted on the cane during mechanical harvesting only accelerates this decay.

Milling

Sugar mills at an old plantation in Antigua.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 wt% 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 color. If a white product is desired, sulfur dioxide may be bubbled through the cane juice prior to evaporation. This bleaches many color-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.