Yeast and Biofuel Biofuels are fuel that are produced through biological processes. This is different than fossil fuels because they are produced by geological processes. Fossil fuels are fossilized organic matter that needs to be burned to produce energy. Biofuel is made of plants, grasses, and roots. By involving yeast to sugar plants fermentation can occur. Thy by product ethanol is produced. This alcohol can be harnessed and used to create energy for running cars, machines, and other combustible mechanisms.