NOVELTY - Production (P1) of ethanol comprising: (a) contacting biomass with aqueous solution containing ammonia, in concentration sufficient to maintain alkaline pH of the biomass-aqueous ammonia mixture (preferably less than 12 wt.% and such that the dry weight of biomass is at a high solids concentration of at least 15 wt.% relative to biomass-aqueous ammonia mixture); (b) contacting product of step (a) with a saccharification enzyme consortium to produce fermentable sugars; and (c) contacting the product of step (b) under fermentation conditions with a suitable biocatalyst to produce ethanol.    USE - For producing ethanol from treated biomass e.g. from bioenergy crops, agricultural residues, municipal solid waste, industrial solid waste, yard waste, wood and forestry waste including e.g. switchgrass, waste paper, corn grain, corn cobs, con grasses, wheat, wheat straw, hay, barley, barley straw, rice straw, sugar cane bagasse, sorghum, soy, components obtained from processing of grains, trees, branches, roots, leaves, wood chips, sawdust, shrubs and bushes, vegetables, fruits, flowers and animal manure (claimed).    ADVANTAGE - Ammonia partitions into a liquid phase and vapor phase. Gaseous ammonia can diffuse more easily through biomass resulting in more efficacious pretreatment at lower concentrations. Ammonia also competes with hydrolysis via ammonolysis of acetyl esters in biomass to form acetamide. Acetamide is less toxic than acetate to certain fermentation organisms which produce ethanol, such as Zymomonas mobilis. Thus conversion of acetyl esters to acetamide rather than to acetic acid reduces the need to remove acetic acid. The use of ammonia also reduces the requirement to supplement growth medium used during fermentation with a nitrogen source. In addition, ammonia is a low-cost material and can also be recycled to the pretreatment reactor during pretreatment or following pretreatment, thus enabling a more economical process. The use of ammonia during pretreatment provides a nitrogen source and reduces or eliminates the need to supplement the growth medium used during fermentation with a nitrogen source.