Theoretical considerations show that very high gravity fermentation technology promotes considerable savings of water and increased plant productivity and therefore results in reduced fermentation and distillation costs per liter of ethanol. Formulae are derived to permit calculation of the amounts of grain and water required to prepare mashes with predetermined concentrations of dissolved solids and insoluble materials. Practical and theoretical methods are described to determine the quantity of the liquid portion of the mash before and after fermentation. Using these values, the efficiency of mashing and fermentation can be calculated. A theoretical method is also presented to predict the maximum concentration of ethanol in fermented mash. These calculations, unlike those used currently in industry, take into account changes in the weight and volume of mash during fermentation.