Sugar beet (Beta vulgaris L.) belongs to the subfamily of the Chenopodiaceae and to the Family of the Amaranthaceae. Its roots contain a high concentration of sucrose and therefore it is grown commercially for sugar production. The three largest sugar beet producers worldwide are the European Union, the United States, and Russia. Only Europe and Ukraine are significant exporters of sugar from beet. Ukraine and Russia have the largest cultivated area, but the largest producers by volume are France and Germany. Apart from the food industry, sugar beets are a valuable feedstock for bioethanol especially in France [1-2].
Sugar beet is a hardy biennial plant that can be grown commercially in a wide variety of temperate climates. During growth it produces a large (1–2 kg) storage root whose dry mass is 15–20% sucrose by weight. This sucrose and the other nutrients in the root are consumed to produce the plant's flowers and seeds if it is not harvested in the first year. In commercial beet production, the root is harvested in the first growing season, when the root is at its maximum size. Beets are planted from small seeds. In most temperate climates, beets are planted in spring and harvested in autumn. A minimum growing season of 100 days can produce commercially viable sugar beet crops. In warmer climates, sugar beets can be cultivated as winter crop, being planted in the autumn and harvested in the spring [3-4].
Harvesting of sugar beets is entirely mechanical. The sugar beet harvester chops the leaf and crown which is high in non-sugar impurities from the root. It further lifts the root, and removes excess soil from the root in a single pass over the field. A modern harvester is typically able to cover 6 rows at the same time. The beet is usually left in piles on the field and then delivered to the factory. Thereby sugar beets do not have to be stored too long as it quickly deteriorates and modifies the sugar molecules.
Due to concerns about the potential survival of pests in the soil, the beets can be cultivated only every three years on the same field. The yields strongly depend on climatic conditions. Sugar beets generate good yields in many temperate settings, but compared to sugar cane, they are a more chemical- and energyintensive crop. Since sugar beets are a more expensive feedstock for fuel production than sugar cane, the economic competitiveness often depends on governmental protection through subsidies and import duties especially for cane sugar (WWI 2006 p. 23f).
Sugar cane (Saccharum sp.) is a genus of 37 species of tall grasses and belongs to the family of the Poaceae and is native to warm temperate to tropical regions. All the species interbreed, and the major commercial cultivars are complex hybrids. Sugarcane is a grass originally from tropical Southeast Asia. The plants have stout, jointed fibrous stalks which are 2 to 6 meters tall and rich in a sugar bearing sap. Today about 107 countries grow sugar cane whereas Brazil is the world leading producer. Sugar cane is the most significant crop for biofuel production today, supplying more than 40 % of all fuel ethanol (WWI 2006 p. 22). Besides the production of bioethanol, sugar cane is also used for the production of alimentary sugar, molasses, and rum.
Sugarcane cultivation requires a tropical or subtropical climate, with a minimum of 600- 850 mm of annual moisture. It is one of the most efficient plants in photosynthesis which is able to convert up to 2 % of incident solar energy into biomass. In prime growing regions, sugarcane can produce up to 20 kg for each square meter exposed to the sun.
Sugarcane is propagated from cuttings, rather than from seeds. Modern methods of stem cuttings have become the most common method of reproduction. Once planted, a stand of cane can be harvested several times as the cane continuously sends up new stalks. Usually, each successive harvest gives a smaller yield, and eventually the declining yields justify replanting. Depending on agricultural practice, two to ten harvests may be possible between plantings.
Sugar cane is harvested by using a sugarcane combine or a chopper harvester. Nevertheless more than half of the world's production is still harvested manually, especially in the developing world. When harvested by hand, the field is first set on fire, burning away dry and dead leaves, and killing venomous snakes, but leaving the water-rich stalks and roots unharmed. Once the cane is cut, it rapidly begins to modify its sugar molecules. Damage on the cane caused during harvesting accelerates this decay.
The juice from sugar cane is further processed, refined, fermented and distilled for bioethanol production. In a sugar mill the harvested sugarcane is washed, chopped, and shredded by revolving knives. The shredded cane is repeatedly mixed with water and crushed between rollers. The collected juice contains 10–15 % sucrose. The remaining fibrous solids, also called bagasse, can be used as co-product to generate process heat. It makes a sugar mill more than self-sufficient in energy. The surplus bagasse can be used for animal feed, in paper manufacture, or burned to generate electricity for the local power grid.
- AGQM (Arbeitsgemeinschaft Qualitätsmanagement Biodiesel E.V.) (2006): Internet: http://www.agqm-biodiesel.de/3.html [12.06.06]
- Armstrong S.R. (1999): Ethanol Brief Report on its Use in Gasoline. – Internet:http://www.ethanol.org/pdfs/health_impacts.p df [02.08.06]
- Arnold K. Ramesohl S. Fischerdick M. Merten F. (2005): Synopsis of German and European erperience and state of the art of biofuels for transport. – Study commissioned by the German GTZ; Wuppertal Institute; 91 p.
- Australian government (2005): Setting National Fuel Quality Standards – Proposed Fuel Quality Standard for Fuel Grade Ethanol. – Austrian Government Position; Canberra; July 2005; 13 p.