Tests were performed in a continuous stirred tank reactor (CSTR), with and without cell recycling, to produce ethanol. The reactor without cell recycling produced the kinetic model of ethanol production, whereas the reactor with tell recycling allowed for a study of process stability. The Levenspiel kinetic model was adopted; however, in the case of fermentation with cell recycling, the coefficient of cell death was added. It was observed that cellular viability varied greatly throughout the fermenting process and that microaeration is of fundamental importance in maintaining the stability of the process.