NOVELTY - Treating (M1) biomass involves: (A) providing biomass with dry matter content of at least 60%; (B) charging a static pretreatment vessel with the biomass of step A); (C) contacting the biomass at least 4% anhydrous ammonia measured as a function of dry weight of the biomass in the vessel, under conditions, thus the total moisture content in the vessel remains below 40 wt.% measured as a function of total mass in the vessel, thus a majority of the biomass is permeated by ammonia vapor; and (D) venting the vessel to remove vapor, where the biomass in the vessel is pretreated.    USE - For treating biomass (selected from cellulosic biomass comprising cellulose, hemicellulose and lignin, corn cobs, corn husks, corn stover, grasses, wheat straw, barley straw, oat straw, canola straw, hay, rice straw, switchgrass, miscanthus, cord grass, reed canary grass, waste paper, sugar cane bagasse, sorghum bagasse or stover, soybean stover, components obtained from milling of grains, trees, branches, roots, leaves, wood chips, sawdust, shrubs and bushes, vegetables, fruits, flowers and animal manure) to produce a pretreated biomass product (claimed) for obtaining fermentable sugar; for production of readily saccharifiable material. The biomass includes other crop residues, forestry wastes such as aspen wood, other hardwoods, softwood and sawdust; and post-consumer waste paper products; and fiber process residues such as corn fiber, beet pulp, pulp mill fines and rejects.    ADVANTAGE - The method uses anhydrous ammonia which is effective in a static reactor vessel when the ammonia can penetrate through the biomass particles or pieces in vapor state, and when biomass is continuously fed and moved through the reactor. The pretreated biomass product is effectively saccharified to produce fermentable sugars for biocatalyst production of a product. The method effectively pretreats biomass with ammonia, producing a readily saccharifiable material that reduces reactor costs. The pretreatment is performed in a static reactor by continuous feeding of biomass to the reactor and moving the biomass through the reactor, with no mechanical mixing, thus removing energy and maintenance costs associated with a mixing reactor where ammonia is a reactant.