NOVELTY - System for producing biogas (16) from biomass (14), comprises: digestion reservoir (20) having path defined by passageways (32) along which biomass is conveyed and digested, where digestion reservoir has inlet and outlet; and at least one mixing assembly (40) located along the path, where each mixing assembly is operatively connected between different passageway segments of path so as to selectively mix given biomass from one segment to another, to increase overall production of biogas along the path.    USE - The system is useful for producing: biogas from biomass; and methane (all claimed).    ADVANTAGE - The system: increases the total production of biogas, thus increasing profitability and avoiding significant downtime periods in energy production; and provides biogas which has relatively high energy potential.    DETAILED DESCRIPTION - System for producing biogas (16) from biomass (14), comprises: a digestion reservoir (20) having a path defined by passageways (32) along which biomass is conveyed and digested, where the digestion reservoir has an inlet fluidly connected to the path for receiving biomass to be digested, and an outlet fluidly connected to the path for releasing digested biomass, and the digestion reservoir is further configured for containing biogas generated from a digestion of biomass along the path; and at least one mixing assembly (40) located along the path, where each mixing assembly is operatively connected between different passageway segments of the path so as to selectively mix given biomass from one segment to another, to increase overall production of biogas along the path. INDEPENDENT CLAIMS are also included for:    (1) a kit with components for assembling the system; and    (2) producing biogas from biomass, comprising (a) providing the system, (b) conveying and digesting biomass along the path of the digestion reservoir, and (c) transferring given biomass from one passageway to another to increase overall production of biogas along the path.    DESCRIPTION OF DRAWING(S) - The figure shows an exposed side elevational view of a reservoir with organic matter and biogas.    Biomass (14)    Biogas (16)    Digestion reservoir (20)    Passageways (32)    Mixing assembly (40)