The processes used to produce bio-based products from biomass belong to four main groups:

• Mechanical or physical processes: (milling, separation, upgrading, dehydration etc.) are mainly used as biomass pre-treatments or in intermediate processing stages;
• Chemical processes (hydrolysis, oxidation etc.) are also mainly used as biomass pre-treatments or in intermediate processing stages;
• Biochemical processes (anaerobic digestion, fermentation, transesterification etc.). Fermentation processes have been used since World War I for industrial production of energy carriers and chemicals. Many bio-based chemicals are now manufactured by fermentation at an industrial scale, such as ethanol, lactate, amino acids and citric acid with the potential to produce many more. Apart from sugar and starch feedstock, lignocellulosic feedstock is also tested in more advanced fermentation systems. Anaerobic digestion is a well-established process for biogas production
• Thermochemical processes (combustion, gasification, pyrolysis etc.) are suitable for the conversion of lignocellulosic feedstock, such as wood. Incineration is the most widely used process to produce bioenergy for heat or power. Gasification technologies are under development and few large commercial units exist, mainly in areas with substantial forestry biomass capacity. Pyrolysis technologies are not yet fully commercially mature with a number of pilot plants in use worldwide and they can be economically efficient for Combined Heat and Power (CHP) only or in a biorefinery concept where both energy and other products of higher value are produced. Liquefaction and torrefaction of biomass are not well developed and are expensive, although they have several potential applications.