A fermentation process for the production of ethanol from natural sources, such as corn, comprising introducing a fermentable sugar and an inoculant, and a bacteriophage cocktail into a fermentation system and introducing a cocktail comprising one or more lytic bacteriophage is added to one or more of the fermentable sugar, the inoculant, or the fermentation system. Bacteriophages that infect and lyse the bacteria that contaminate fermentable sugars are selected. The bacteriophage cocktail is added in an amount effective to substantially prevent growth of these bacteria.