How Sweet It Is Back to Map Page Brazil The term sugar is applied in general to carbohydrates that are water-soluble, lacking in color and odor, sweet in taste, and able to crystallize. More specifically, sugar is used to mean common table sugar, or sucrose, a compound produced by plants. About 60% of the world's sugar is supplied by the stem of sugarcane, while the other 40% comes from the root of the sugar beet, making these two plants the only commercially important sources of sucrose. According to figures from the Food and Agriculture Organization (FAO), more than 1,214,293,000 metric tons of cane sugar and 270,252,800 metric tons of beet sugar were produced in 1997. Countries producing the largest amount of sugar include Brazil and Cuba. Structures of glucose and fructose molecules The carbohydrates produced by sugarcane and sugar beets are chemically identical. Carbohydrates, the most abundant organic compounds in nature, contain carbon, hydrogen, and oxygen, and are typically expressed as Cm(H20)n. The carbohydrate group is further subdivided into monosaccharides, disaccharides, and polysaccharides. Monosaccharides, such as glucose, fructose, and ribose, are simple sugars with three to seven carbon atoms. Disaccharides are formed when two monosaccharides bond together. Sucrose, for example, is a disaccharide formed from a molecule of glucose and a molecule of fructose. Polysaccharides, which are three or more monosaccharides bonded together, include starch and cellulose, each potentially containing thousands of glucose molecules attached at specific points. Plants produce carbohydrates through the metabolic process of photosynthesis, in which radiant energy is used to convert inorganic carbon into organic carbon. The photosynthetic reaction is summarized in the following equation: CO2 + H2O + radiant energy---->Cm(H20)n + O2 + H2O + ATP According to the pressure-flow hypothesis, carbohydrates are shuttled between sources such as food storage tissue and sinks where they are utilized. Scientists have determined that the transport molecules within plants are mainly carbohydrates. They discovered this by studying aphids, which derive nutrition by inserting their stylets into the lumens of sieve-tube elements in phloem tissue. Carbohydrates, representing 90% of the organic molecules within the phloem, are mostly in the form of sucrose. The sugarcane and sugar beet plants retain and store the sucrose, instead of converting it to starch after it is unloaded from the phloem as most other plants do. Sugarcane stores sucrose in the cells of the stem, while the sugar beet stores the sucrose in the cells of the root. Sugarcane, Saccharum officinarum, is a perennial grass in the Poaceae family. These cultivated monocots are believed to have originated from wild-type populati Various forms of processed sugar ons in Oceania. The Poaceae family, also known as Gramineae, is represented by 635 genera and 9,000 species. While there are tropical, subtropical, and a few temperate species in the Poaceae, Saccharum is mainly a tropical genus. Molasses, the uncrystallizable portion of sugar, is an economically valuable by-product of the refining process. It is used as a table syrup and a food flavoring as well as in the manufacture of some processed tobacco. In Madagascar, the juices of Saccharum are fermented into a beverage called "betsa-betsa." The alcoholic beverage rum is the distillate of fermented molasses. After the stems of S. officinarum are processed for sucrose, the remaining crushed stems, called bagasse, are used as a fuel in mills, made into fiberboard, or mixed with molasses for cattle feed. Because tropical conditions were necessary to grow sugarcane, honey remained the primary sweetener in Europe until almost 1500. The scarcity of sugar made it very expensive-a pound was sold for the equivalent of $110 today. As a result, sugar was primarily used in medicinal preparations to make bitter herbal remedies more palatable. Not until the colonization of the New World did Europeans acquire land suitable for growing sugarcane. In 1493, crops were established in the West Indies, which became the center of both the American and British sugar-trading triangles in the late seventeenth and early eighteenth centuries. Eventually, sugarcane was harvested on the islands of Hispaniola and Puerto Rico, as well as on other Caribbean islands and in South America, with sugar plantations established in Brazil in 1521. According to the USDA's International Agricultural Trade Report, Brazil is today the largest producer and exporter of sugar.   Sugarcane growing in Benin (Africa). The stem of sugarcane, often called the cane, attains a height of 15 to 20 feet and a diameter of about 5 inches. Since sugarcane can propagate vegetatively, segments containing nodes, called setts, are planted. Roots develop from the node and produce a new plant with harvestable cane in 20-24 months. Sugarcane undergoes C4 photosynthesis, a type of photosynthesis considered very efficient in high- temperature areas. With its typical Krantz anatomy, the photosynthetic rate is two or three times higher than that of C3 plants.  After the cane is stripped of its leaves, the stems are crushed and shredded in rollers while hot water is sprayed over them to dissolve out any additional sucrose.  The extracted juice is mixed with calcium hydroxide to reduce acidity and then boiled to kill microorganisms. After being filtered and evaporated under partial vacuum, the resulting thick syrup contains many sugar crystals and is referred to as massecuite. The massecuite is centrifuged so that the crystals separate from the molasses. Sugar beets, Beta vulgaris, are in the Chenopodiaceae family. This family of dicots is represented by 120 genera and 1,300 species, many of which are commonly found in desert and semi-desert areas. The characteristic red color of the beet is due to betalain pigments. Another economically valuable genus within the Chenopodiaceae is spinach (Spinacia sp.). In the eighteenth century, German scientists noted that the root of B. vulgaris, though too tough and fibrous to be eaten by humans as a vegetable, contained high amounts of sugar. Selective breeding for high sucrose content has resulted in up to 20% of the root's total weight in sucrose, compared to sugarcane, in which sucrose comprises a still impressive 15% of the cane's total weight. In 1747, a way to extract sugar from beets was first developed in Germany, but the process was not perfected until 1877. By 1890, sugar beets were being cultivated in the United States and Europe. Although B. vulgaris is a biennial, it is harvested at the end of the first year, when the sucrose content is highest. The aerial portion of the sugar beet is used as cattle feed, while the roots are cut into smaller pieces to facilitate crushing and juice extraction. The pulp that remains after crushing and extracting is a very rich food for domesticated animals. Calcium hydroxide is then added to the extracted juice; the remainder of the process is similar to that used to make cane sugar. References, Websites, and Further Reading Levetin, Estelle, and Karen McMahon. 1999. Plants and society, 2d ed. New York: McGraw-Hill Companies, pp. 56-58. Simpson, B.B., and Molly C. Ogorzaly. 2001. Economic botany: Plants in our world, 3d ed. New York: McGraw-Hill Companies. Sugar," Microsoft® Encarta® Online Encyclopedia 2000. © 1997-2000, Microsoft Corporation. http://encarta.msn.com The American Sugar Alliance http://www.sugaralliance.org/ The United States Department of Agriculture, Foreign Agricultural Service, The commodity SUGAR http://www.fas.usda.gov/htp/sugar/sugar.html Related Reading in Stern, Introductory Plant Biology, 8th Edition Chapter 2: The Nature of Life The Elements: Units of Matter, pp. 15-16 The pH scale, p. 20 Chemical Components of Cells, pp. 21-23 Chapter 4: Tissues Complex Tissues: Xylem; Phloem, pp. 54-57 Chapter 5: Roots and Soils How Roots Develop, p. 63 Specialized Roots: Food-Storage Roots, pp. 69-70 Chapter 6: Stems Origin and Development of Stems, pp. 85-87 Herbaceous and Woody Dicotyledonous Stems, pp. 88-93 Monocotyledonous Stems, pp. 93-95 Chapter 8: Flowers, Fruits, and Seeds Annuals, Perennials, and Biennials, pp. 127-29 Differences Between Dicots and Monocots, including Table 8.1, pp. 129-30 Chapter 9: Water in Plants Transport of Food Substances (Organic Solutes) in Solution, p. 159 The Pressure-Flow Hypothesis, p. 159 Chapter 10: Plant Metabolism Photosynthesis, pp. 166-75 The 4-Carbon Pathway, p. 176 Krantz Anatomy, Figures 10.11 and 10.12, pp. 176-77 Fermentation, p. 178 Chapter 14: Plant Propagation and Biotechnology Traditional Vegetative Propagation, pp. 238-40 Propagation from Specialized Stems and Roots, pp. 240-42 Chapter 24: Flowering Plants and Civilization Monocots: The Grass Family (Poaceae), p. 454