Converting this biomass to a useable fermentation feedstock (typically some form of sugar) can be achieved using a variety of different process technologies. These processes for fermentation feedstock production constitute the critical differences among all of the bioethanol technology options.

Fermenting the biomass intermediates using biocatalysts (microorganisms including yeast and bacteria) to produce ethanol in a relatively dilute aqueous solution is probably the oldest form of biotechnology developed by humankind.

Processing the fermentation product yields fuel-grade ethanol and byproducts that can be used to produce other fuels, chemicals, heat and/or electricity.

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