A high final ethanol concentration during ethanol production will improve the plant profitability by reducing water usage, increasing the plant capacity, and decreasing the downstream processing costs, thereby improving plant efficiency. High final ethanol concentrations (i.e., >14 %) can be achieved by high-gravity fermentation. At a high initial dry solids content (~33 %), it is particularly important to ensure that the nutritional needs of the yeast are appropriately met as a preventive measure to avoid stuck or sluggish fermentations.
It has been found that temperature staging (33 C during early stage and 28 C or lower during later stages) is also important to complete a high-gravity mash; The addition of proteases, urea, Mg2+, yeast extracts, and amino acids, have all been reported to provide useful nutrients to yeasts, thereby increasing fermentation rates and final ethanol concentrations in high-gravity mashes.
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