Bioenergy encompasses all energy produced from biomass (which represents more than 80% of energy production in this sector) or biofuels. In Portugal, the prominent biofuel is biogas, a mixture of gases produced by the biological decomposition of organic matter in the absence of oxygen. Biomass is all organic matter of plant or animal origin capable of regenerating in a short period of time and in a sustainable way. Biomass includes byproducts of forestry, agriculture, livestock farming, and municipal solid organic waste. In forest biomass power plants, electricity is produced through the direct combustion of biomass. This combustion allows for the production of heat energy that transforms liquid water into steam, which in turn is used to move turbines and power electric generators. Although this process releases CO₂ into the atmosphere, the CO₂ emissions balance is zero, since the plants that gave rise to the fuel absorb quantities of CO₂ during their life cycle that offset the emissions.