Sugar cane (Saccharum officinarum)
POACEAE, Grass Family
One of the most important species of food-producing grasses is sugar cane (Saccharum officinarum). Of the major crop grasses, cane is remarkable because this is a perennial. Typically, a stem of sugar cane grows to a height of 4 or 5 meters in 11 to 18 months and then produces a flower stalk. Just when a flower stalk forms, the solid stem of this plant is loaded with sucrose, which can be easily removed from the stem by crushing, eaten raw or then concentrated to produce crystallized sugar and other sugar derivatives.
The primitive forms of sugar cane came from Asia. Experts surmise that this crop plant arose as a hybrid between several species of Saccharum. Some workers guess that it was first cultivated in New Guinea and Indonesia, whereas others point to India, where several species of Saccharum are still under cultivation. Sugar cane was taken to Europe by Alexander the Great as a competitor to honey, and it was widely planted in Egypt by Arabs in the Middle Ages. This crop was introduced to the West Indies by Columbus and was already cultivated in Brazil in the 1530s. By 1753, sugar cane was commercially grown in Louisiana.
Traditional ways of cane propagation are vegetative. Stems are cut into pieces a foot long with about three nodes (a sett). Setts are laid in shallow furrows in a cleared field and then covered with a thin layer of soil. In several days the nodes sprout, producing aerial shoots, roots, and underground stems (rhizomes). New rhizomes send up innumerable shoots, resulting soon in a dense stand of shoots.
Sugar cane has one of the highest growth rates of any plant, so in 18 months (8-30), after the rainy season and before fruits can develop (they normally do not develop fruits anyway), the stems are harvested. Often the field is burned (another view) or topped to eliminate the leaves, which have little sugar. Leaves are left in the field to be grazed by cattle and to decompose, thus returning nutrients to the soil. Harvesting is usually done with machetes, which requires abundant, cheap labor. Simply stated, this meant that slaves were needed in the Americas to run this industry. Even today, the cheap price of sugar requires low wages for field hands, if efficient mechanization is not used.
Stems are subdivided into 4-foot lengths and transported in carts or rail cars to a nearby factory. Cane must be processed within two days of harvesting, otherwise fermentation and bacterial growth destroy the crop and the sugar content decreases sharply. Stems are harvested when sucrose content in the stems is 12-20%. At the sugar mill, which works around the clock, the fresh stems are fed into a mechanical crusher. Originally, the crushers were hand- or animal-turned wooden rollers, but now they are steel ones. Crushing may have to be repeated several times. Much solid waste remains at the sugar mill from the crushed stems. This is called bagasse. Water is added to the thick, brown sap, which is boiled. Sometimes lime water (alkali) is added to help remove impurities, which must be filtered out. The purified syrup is concentrated to a stage called massecuite, a mixture of brown sugar crystals and liquid molasses, which are then separated by centrifugation. White sugar is made from the brown crystals by redissolving and chemically bleaching (see below) to remove all iron and protein. Hence, brown sugar is slightly more healthful than white sugar. Molasses can be used immediately for cooking, silage, and the manufacture of rum by fermentation. Some molasses is also used as a sugar source for making vinegar.
Mechanization has greatly improved production in places like Queensland, Australia and Hawaii, where labor is not cheap. Fertilizers greatly increase production. Several decades ago on Hawaiian plantations, which were fertilized and mechanized, one could obtain up to 100 tons of cane per acre (= 9 tons of refined sugar). Forms used today are special hybrids that were developed through intensive breeding of Saccharum officinarum with the other species in the genus.
Development of the sugar cane industry in the United States increased with the Cuban embargo, so that up until recently this was an important crop in Louisiana, Florida, Texas, and especially Hawaii. Whereas the Hawaiian Islands were, for more than a century, a prime source of domestically grown sugar cane, acreage devoted to sugar cane from 1992-1996 was halved, and by 1996 all cane fields on Oahu and Hawaii were retired, to be used instead for vegetables, macadamia nuts (Macadamia ternifolia), coffee (Coffea), tropical flowers, bananas, and timber, and leaving only the four most efficient growers on Maui and Kauai still in production (84,000 acres). In Louisiana, where sugar plantations have been commercially viable, bagasse has been recycled for many years, being baled to be used in the 1970s to manufacture ceiling tile, building board, and paper, and now to generate steam for sugar cane processing and as a garden mulch.
Sugar cane has become a valuable renewable natural resource in Brazil, where it is used to produce large quantities of ethanol, which is used in automobiles in place of gasoline.
Raw sugar crystal, obtained from the crushed stems of sugar cane or the roots of sugar beets (Beta vulgaris), is yellowish or brownish, because the sugar crystals are covered with a thin film of molasses and contain organic and inorganic impurities. To obtain pure white, small sugar crystals, raw sugar must be refined. Sugar refining is demanded by most world consumers and for foods, especially baked goods, confectioneries, cereals, beverages, and sweetened canned goods. So important to French culture was refined sugar that Napoleon in 1811 started the domestic sugar beet industry because of a British blockade. Sugar beets are grown in temperate zones in user countries, and the sugar is refined where the raw sugar is extracted. Cane sugar, however, is grown in the tropics but, for economic reasons, is often processed in user countries.
Raw sugar from the tropics is loaded via conveyor belts into the holds of large ocean-going ships. The ship is unloaded with cranes and caterpillars at the refinery, where the raw sugar is stored in a large, dry warehouse. Raw sugar keeps a long time if kept dry and awy from the bees; few pests thrive on raw sugar.
First in refining, a film of molasses is removed from the crystals in centrifuge machines. The sugar crystals are then melted in hot water and screened to remove crude trash (sticks, leaves, rodent dung, etc.) before the liquid sugar goes to the filter house. Here the sugar is passed through sweetened cloth, which has such small pores that it removes even the bacteria. Phosphoric acid is commonly added as a bleaching agent, because it releases the iron in sugar. If iron is present in sugar, the crystals grays with age. Liquid sugar is finally put through charcoal filters made of granular bone charcoals, made from bones of African mammals. Nonsugar impurities are adsorbed on the charcoal, yielding a clear solution.
Liquid sugar is concentrated by boiling in vacuum pans and spun in centrifuges to separate syrup from crystals. The last syrup is removed by spraying with hot water. In a granulator, the crystals are broken down to uniform size. The final product is pure sucrose, with the iron, protein, and any other organic residues removed.