Biofuels are combustible fuels created from biomass; in other words, fuels created from recently living plant matter as opposed to ancient plant matter in hydrocarbons. The term biofuel is usually used to reference liquid fuels, such as ethanol and biodiesel that are used as replacements for transportation fuels like petroleum, diesel and jet fuel. Biofuels can also include solid fuels like wood pellets and biogas or syngas – however in this summary we will focus on liquid fuels.
There are two main types of biofuels – ethanol and biodiesel. The simplest way to distinguish between the two is to remember ethanol is an alcohol and biodiesel is an oil. Ethanol is an alcohol formed by fermentation and can be used as a replacement for, or additive to, gasoline whereas biodiesel is produced by extracting naturally occurring oils from plants and seeds in a process called transesterification. Biodiesel can be combusted in diesel engines.