So far, the largest biofuels efforts have involved the age-old process of converting sugars in plants into ethanol. If biofuels are ever to make a significant dent in fossil fuel use, however, they're probably going to have to be made from something that can't also be used as food (either by us or our farm animals.) That means working with something other than sugar.

The leading candidate is cellulose, a robust polymer of sugars that give plants the strength to grow several hundred feet tall. Breaking down cellulose into sugars (which can then be converted into ethanol) is not easy to do economically, although a lot of research has gone into finding processes that work. A leading candidate for this is to use the enzymes from bacteria and fungi that normally decompose wood. The US Energy Information Agency has announced that the nation's first commercial-scale plant based on this approach has just opened in Iowa.

"Project Liberty," the result of a joint venture between US-based POET and the Netherlands' Royal DSM, will have the capacity to process over 750 tons of corn stover each day. Stover is the inedible parts of the plant: husks, cobs, the stalk and leaves. Although intended to work with corn (hence the Iowa location), it's possible that the facility could be used for other sources of cellulose, like grasses.

The EIA says that Project Liberty is one of three commercial facilities that will launch in the near future. Collectively, they'll provide the capacity to produce over 75 million gallons of ethanol each year. That sounds great, but the government had once projected that over a billion gallons would be produced—in 2013. So, clearly the industry is running a bit behind. That said, testing how the digestion of cellulose scales up to these levels will be critical to understanding if and when the process can be competitive with fossil fuels.