BACKGROUND The purpose of this study was to evaluate the juice of the fescue grain sorghum, since it is a low‐cost agricultural waste, for the production of bioethanol to be used as a gasoline additive. In addition, the octane number has been investigated by varying the ethanol‐gasoline mixture 2, 6 and 10%. RESULTS The wort fermentation was carried out with commercial bread yeast (Saccharomyces cerevisiae). The liquor obtained was characterized and quantified through gas chromatography. Bioethanol–gasoline mixtures were prepared as: 2, 6 and 10% v/v to determine their octane index. Bioethanol was purified in a fractional distillation tower, attaining thereby a 93.5% purity: lastly, it was dehydrated through molecular sieves to obtain a 99.2% final purity bioethanol. Spectroscopy aided also to determine that the bioethanol–gasoline mixture containing 10% ethanol attained an octane index of 89, which is the value required for commercial gasoline in Mexico. CONCLUSION The bioethanol obtained from the fermentation of juice of fescue grain sorghum is indeed viable to be used as additive in gasolines. The fermentation can be carried out with the bread yeast, at the natural pH of the juice and without the addition of nutrients, which leads to an attractive economic process. © 2019 Society of Chemical Industry