In order to establish a metabolic flux analysis applied to ethanol production an user interface based on the program METATOOL using C language combined with MSEXCEL was developed. It has built a metabolic network composed of 42 metabolic reactions including glicolysis, pentose, citric acid and ammonium assimilation pathways. It was found 23 solutions for the metabolic flux vector, in which 11 are valid experimentally. There was a maximum yield for ethanol production (YEtOH / S) of 0.51 g / g. It was found consistent with previous studies. With the results it was identified the carbon flux distribution to produce ethanol and glycerol, which opens the possibility for increasing the yield of ethanol by manipulating strains of Saccharomyces cerevisiae.