NOVELTY - Method for increasing overall rate of ethanol production by microorganism selected from yeast and natural and/or genetically engineered bacterium during fermentation of sugars in fermentation medium, where sugars are derived from a feedstock substrate consisting of e.g. corn, wheat, or rye involves: adding emulsion comprising monoterpene and surfactant to fermentation medium in amount to improve viability of yeast or genetically engineered bacterium, so as to increase overall rate of ethanol production as primary product of fermentation.    USE - For increasing overall rate of ethanol production by microorganism selected from yeast and natural and/or genetically engineered bacterium during fermentation of sugars (claimed). The ethanol is useful as fuel.    ADVANTAGE - The use of composition of terpene and surfactant improves viability of yeast/bacterium, and increases rate and/or yield of production of ethanol, preferably increases overall rate of ethanol production as primary product of fermentation. Thus composition reduces frequency of plant shutdowns for cleaning and sanitizing and results in reduced cleaning requirements for fermentation operation; is easy to administer; does not interfere with operation of fermentation plant; reduces competition from bacteria; reduces undesirable side products; improves operating conditions; and is cost effective. The composition increases rate of fermentation in initial stages of sugar fermentation by Saccharomyces sp. yeast by over 75%, and also maintains viability of yeasts at end of a commercial ethanol fermentation by significant amount. These effects result in improvements in cost and ease of operation of fermentation operations in bioethanol plants. The surfactant(s) reduce interfacial tension, allowing for formation of small emulsion droplets, where small droplet size is preferred to minimize the rate of gravity separation of phases of emulsion.    DETAILED DESCRIPTION - Method for increasing overall rate of ethanol production by a microorganism selected from a yeast and natural and/or a genetically engineered bacterium during fermentation of sugars in a fermentation medium, where the sugars are derived from a feedstock substrate consisting of corn, wheat, rye, barley, cassaya, millet, potato, cellulose, molasses, fruit, cane juice, and/or beet juice, involves: adding an emulsion comprising a monoterpene and a surfactant to the fermentation medium in amount to improve viability of yeast or genetically engineered bacterium, so as to increase the overall rate of ethanol production as primary product of fermentation.