Sugars, through the process called cellular respiration, are the primary power sources used to produce adenosine triphosphate (ATP), the energy exchange molecule that sustains all life.
Energy is stored in organisms as starch or fat but is burned as sugar. Sugars include some of the simplest carbohydrates, and they are building blocks of more complicated molecules. Common sugars include glucose, fructose, sucrose,maltose, and lactose.
Alcohol (ethanol) derived from sugar fermentation is an important product to the food and beverage, fuel, and drug manufacturing industries. The primary sugar derived from plants is sucrose, a disaccharide composed of two simpler sugars, glucose and fructose, joined together.
History of Use in Food
Demand for sugar and other food flavorings was particularly strong before canning and refrigeration. People often had to eat partially spoiled food, and they eagerly sought ways to improve its flavor. Items with high sugar levels, such as berries and grapes, were especially prized.
Sugarcane (Saccharum officinarum y officinarum) has a stem that can be squeezed to deliver a sucrose-rich syrup, and the leftover woody material (bagasse) can be dried and burned to boil off water. Molasses syrup or solid sugar can be made in this way.
Arab traders brought sugarcane to Europe in the 1100’s. By the 1500’s European colonization in Brazil and the Caribbean provided rich growing fields. So important and valuable were sugar crops that in 1800 the new countries of Haiti and the United States had similar gross national products.
However, the cravings and rivalries that created sugar empires caused their decline. England and its allies fought a series of wars with France in the late 1700’s and early 1800’s, and British blockades kept molasses out of Europe.
France’s Napoleon responded by offering a prize for a process to produce sugar from a European-grown plant. A sugar beet process won, and cane sugar was never again as centrally important.
Meanwhile, cane roots steadily grow and increase humus in the soil. Sugar beets require plowing and are dug from the ground during harvesting, but they, too, leave extensive roots.
When sucrose prices rose in the 1950’s, high-fructose sweeteners were developed as alternatives. Enzymes are used to break starches into fructose.Corn syrup, one fructose sweetener, is cheaper than sucrose and has displaced much U.S. sucrose use. Elsewhere, fructose syrups are made from wheat, rice, tapioca, and cassava.
Sugar and Alcohol
The fermentation of alcohol has been a major aspect of sugar use since antiquity. Fungi called yeasts convert sugars into ethyl alcohol (ethanol); the yeasts can produce only mild alcohol levels. Alcohol, although medically classified as a depressant, can provide a short-term energy boost.
It also acts as a mild poison that desensitizes the central nervous system, allowing drinkers to feel relaxed. Ancient Egyptians and Mesopotamians fermented grains into beer, while Greeks and Phoenicians traded wine from grapes.
In the Middle Ages, alchemists experimented with distillation, a process in which a substance boiled out of one substance is cooled back into liquid elsewhere.Distillation transformed beers and wines into whiskeys and brandies, alcoholic drinks several times more potent.
Caribbean sugar and alcohol formed one leg of the “triangle trade” from the 1600’s through the early 1800’s. New Englanders sold fish for Caribbean molasses, fermented it, and distilled it into rum. They traded rum in Africa for slaves, sold largely in the Caribbean.
Fuel and Other Uses
The energy crisis of 1973 involved oil shortages and soaring prices, and it stimulated many experimental ethanol programs. Most experiments were abandoned when oil prices dropped in the mid-1980’s, but Brazil persevered in a national program of sugar-cane alcohol fuel.
Even Brazilian ethanol is only barely economically competitive with fossil fuels. The major problem is that energy expenditures in the manufacture of ethanol include fuel for tending the fields and gathering cane, energy lost to yeasts (about half, although the yeasts do yield high-protein by-product), and another half of the remainder expended for distilling the material to 95 percent alcohol.
Suggested improvements include developing more efficient yeasts and performing the distillation process under partial vacuum, which would allow continuous processing rather than batch processing.
Theoretically, the most efficient way to use sugar energy would be the development of electrical fuel cells that would take energy from sugar, just as living organisms do.
Losses from yeast digestion and distillation would be eliminated, and a fuel cell might achieve 50 percent efficiency, rather than the 25 percent efficiency of internal combustion engines, yielding eight times more energy.
This approach could create an energy revolution if the technical problems could be overcome. (Energy-efficient processes must be developed for saccharification, or hydrolysis, of cellulose from wood and garbage.)
Sugars can also be nutrients for generating other products. Specialized groups of other cells, such as juice-producing cells from oranges or fiber-producing cells from cotton, can be cultured with sugar nutrients, for example, and genetic engineering has developed yeasts that produce specialty chemicals such as catalysts.