TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: In carrying out liquefaction of biomass slurry in reactor using enzymes, adding enzymes to the biomass slurry in the reactor includes adding enzymes to the biomass slurry in the reactor after each of at least two iterations of the operations of measuring pH of the biomass slurry and adjusting the pH of the biomass slurry as needed to a value within a desired range. Each operation of adjusting the pH of the biomass slurry in the reactor as needed to a value within a desired range includes adding an acid and/or a base to the biomass slurry as needed. Adding an acid and/or a base to the biomass slurry as needed includes adding the acid and/or the base to the biomass slurry as needed in a continuously-stirred region of the reactor. Adjusting the pH of the biomass slurry in the reactor as needed to a value within a desired range includes adjusting the pH of the biomass slurry in the reactor as needed to a value between about 4 and about 6.5. Adding enzymes to the biomass slurry in the reactor includes adding the enzymes to the biomass slurry in a continuously-stirred region of the reactor. The enzymes include cellulase enzymes. The method further comprises measuring viscosity of the biomass slurry in at least one plug flow region of the reactor; discharging the biomass slurry from the liquefaction tower with a viscosity of about 8000 centipoise or less; and retaining the biomass slurry in each plug flow region of the reactor for about five minutes or less and retaining the biomass slurry in each continuously-stirred region of the reactor for about two minute or less. Measuring pH of the biomass slurry in multiple regions of the reactor includes measuring pH of the biomass slurry in multiple plug flow regions of the reactor. Measuring pH of the biomass slurry in multiple regions of the reactor includes measuring pH of the biomass slurry in at least one continuously-stirred region of the reactor. In carrying out liquefaction of pre-treated biomass slurry in liquefaction reactor, adjusting the pH of the biomass slurry measured in the plug flow region as needed includes adding an acid and/or a base to the biomass slurry in the liquefaction reactor as needed. Adding an acid and/or a base to the biomass slurry in the liquefaction reactor as needed includes adding the acid and/or the base to the biomass slurry as needed in a continuously-stirred region of the liquefaction reactor. The desired pH range of the biomass slurry includes a pH range of between about 4 and about 6.5. The method further comprises adding enzymes to the biomass slurry in the liquefaction reactor after adjusting the pH of the biomass slurry measured in the plug flow region as needed to the value within the desired range. Adding enzymes to the biomass slurry in the liquefaction reactor includes adding the enzymes to the biomass slurry in a continuously-stirred region of the liquefaction reactor. A predetermined total amount of enzymes is added to the biomass slurry; where adding enzymes to the biomass slurry after adjusting the initial pH of the slurry to the value within the desired range and before the biomass slurry enters the liquefaction reactor comprises adding about sixty percent or less of the predetermined total amount of enzymes to the biomass slurry; and where adding enzymes to the biomass slurry in the liquefaction reactor after adjusting the pH of the biomass slurry measured in the plug flow region as needed to the value within the desired range comprises adding the remaining amount of the enzymes to the biomass slurry. The method also comprises measuring pH of the biomass slurry in each plug flow region of the liquefaction reactor; and after each the operation of measuring pH of the biomass slurry, adjusting the pH of the biomass slurry in the liquefaction reactor as needed to a value within the desired range. It further comprises measuring viscosity of the biomass slurry in the liquefaction reactor. It also comprises pumping the biomass slurry into the liquefaction tower after the operations of measuring an initial pH of the biomass slurry before the biomass slurry enters the liquefaction reactor, adjusting the initial pH as needed to a value within a desired range, and adding enzymes to the biomass slurry after adjusting the initial pH of the slurry to the value within the desired range and before the biomass slurry enters the liquefaction reactor. Preferred Reactor: The tower reactor further comprises instruments positioned in communication with multiple ones of the plug flow regions and configured to measure viscosity of the biomass slurry in the multiple ones of the plug flow regions. EXAMPLE - No example given.