Sugarcane molasses is a by-product of sugar processing. It is generated during sugar crystallization by evaporation and represents the mother liquor from which the crystals are formed. Most cane molasses used for ethanol production corre­sponds to the C-molasses. Due to the repeated evaporation-centrifugation process, the molasses obtained is a viscous, thick brown liquid with a higher concentra­tion of impurities and mineral salts compared to cane juice. An example of the
average composition of cane molasses is presented in Table 3.6. The data in this table correspond to cane molasses from the United States, Colombia, and Costa Rica (Curtin, 1983; Fajardo and Sarmiento, 2007; Vega-Baudrit et al., 2007). This composition is quite variable because it depends on factors such as the type of soil, temperature, humidity, cane production season, cane variety, type of cane processing in the sugar mill, and storage conditions (Curtin, 1983). This implies great variations in the content of sugar and remaining nutrients in molasses as well as its color, viscosity, and flavor.

The molasses is commercialized based on its degrees Brix, which is an indi­cator of the specific gravity and represents an approximation to its total solid content. The degrees Brix were originally defined for solutions of pure sucrose indicating the percentage (by weight) of this sugar in the solution. However, and besides sucrose, molasses contains other sugars, such as glucose, fructose, and raffinose, as well as a variety of nonsugar organic compounds. In this way, the value of degrees Brix for molasses does not correspond to the content of sugars or total solids. Nevertheless, the degrees Brix are still being used for trading molasses. Cane molasses contains some vitamins that are crucial if considering the subsequent fermentation. For this reason, in general, it is not necessary to add vitamins to the culture medium based on cane molasses for fermentation with the yeasts of the Saccharomyces cerevisiae species. Biotin, pantothenic acid (in the form of pantothenate), and inositol are probably the three vitamins essential for the normal yeast growth. To this regard, the biotin is in excess in cane molasses, while the pantothenate is found in minimal amounts required for fermentation. The inositol is present in adequate amounts in cane molasses (Murtagh, 1995).