GCSE BIOLOGY; When does digestion come in to the ethanol-based fuels production from plant materials?

To generate plant based ethanol fuels, you need microorganisms to digest the structural polysaccharides of plant cell walls (cellulose, lignin, etc...). They break these polymers into single glucose monomers which they then ferment into ethanol. Often this process is referred to as digestion and occurs in reactors called digesters.