TECHNOLOGY FOCUS - BIOLOGY - Preferred Method: The method further involves maintaining the moisture concentration at a first moisture level or within a first moisture range. The method further involves (e) increasing the moisture concentration of the contents of the reactor vessel to a second moisture level; and (f) collecting methane gas from the reactor vessel. The step (e) involves increasing the moisture concentration by introducing water, a liquid stream, a dilution leaching solution, steam or vapor, where there is no chemical agent or heat pretreatment to enrich the bacterial inoculum. In the method, the first moisture concentration of the contents of the reactor vessel is less than 85%. In the method, the first moisture concentration of the contents of the reactor is less than 80%. In the method, the second moisture concentration of the contents of the reactor vessel is greater than 90%. The method further involves maintaining a pH level of the contents of the reactor vessel at a first pH level or within a first pH range. In the method, the biomass feedstock is non-sterile. In the method, the biomass feedstock is pretreated, where the pretreatment is a member selected from acid treatment, steam explosion, and ammonia fiber-freeze explosion. In the method, the biomass feedstock is a residue obtained from a process to produce ethanol, where the biomass feedstock and the bacterial inoculum are introduced into the reactor vessel substantially at the same time. EXAMPLE - Production of hydrogen and methane gas was carried out as follows: each seed sludge (the bacterial inocula containing a mixed anaerobic bacterial community) was inoculated at 10 vol./vol.% into corn stover substrate. Two sets of bottles (150 ml per bottle) for different moisture concentrations (97%, 90%, 83% and 76%) were prepared in duplicate. Then, 0.8 g of sodium bicarbonate was added to the serum bottles. The culture was adjusted to its initial pH with 5 N HCl or 5 N NaOH. The headspace of the bottles was purged with nitrogen gas to eliminate remaining oxygen from the headspace, and the bottles were sealed with butyl rubber stoppers and aluminum crimps. The bottles were then placed in a static incubator with temperature controlled at 35 plus minus 0.5 degrees C to form higher hydrogen/methane gas.