Ethanol is produced by fermenting plant carbohydrates with yeast. Sucrose, commonly called table sugar, is a soluble sugar carbohydrate composed of two simple sugars, fructose and glucose. Sucrose is the main sugar extracted from sugar cane and sugar beets, and is highly soluble in water. Industrial strains of yeast can be used to break down the sucrose into fructose and glucose and ferment the sugars into ethanol. Ethanol production from sucrose predominates in tropical regions with sugar cane production, such as Brazil, which produced 4.2 billion gallons (15 billion liters) of fuel ethanol in 2004.
Fermentation of sucrose from sugar cane can be conducted using the sugar cane juice directly obtained from squeezing the stalks, or from the molasses. Most ethanol plants in Brazil produce ethanol from molasses, typically molasses A, which has had the sugar removed by a single crystallization step. The ethanol concentration in the fermented molasses is about 9% by volume, or 7% by weight. From each gallon of sugar cane molasses, 0.41 gallons of ethanol can be produced. If both the raw sugar and molasses in sugar cane is used to produce ethanol, 19.6 gallons of ethanol can be produced per ton of harvested sugar cane.
The fermentation and ethanol recovery processes for sugarcane juice or molasses use technologies similar to those used to produce ethanol from corn. The fibrous plant material that remains after the juice has been squeezed out of the sugarcane stalk is called bagasse. In most processing facilities, bagasse is burned to produce the heat and steam used to evaporate water from the sugar in the crystallization process, and to distill the ethanol. Bagasse is also used to produce the electricity used by the processing plant, with excess electricity sold to the power grid. However alternatively, bagasse could be used as a cellulosic biomass resource to produce ethanol, other biofuels, and bioproducts.