Building on methods used by farmers to produce silage for feeding livestock, Japanese researchers have developed a technology for simultaneous biofuel and animal feed production which doesn't require off-site processing. The solid-state fermentation (SSF) system captures ethanol produced as a result of fermentation resulting from wrapping rice plants grown to feed livestock in a plastic-covered bale containing yeast, enzymes and bacteria.

Researchers have previously looked into what’s termed "second-generation" biofuel production that uses inedible (for humans at least) organic matter such as wood or straw rather than corn or sugar. The downside is lower efficiency. However, Japanese researchers may have found a way around that.

Non-sterilized whole rice plants plants are packed into a round bale in the field at harvest and wrapped in polyethylene, along with the yeasty mixture. The bales are then left in the field to ferment. After a period of "incubation," ethanol is recovered via one-step distillation using vacuum distillation equipment. What remains after processing can be used as cattle feed.

According to Mitsuo Horita, a researcher at the National Institute for Agro-Environmental Sciences, the SSF system produces high yields of ethanol and silage and, unlike traditional biofuel production, it doesn't compete with human food crops.

It's still early days though. The researchers have yet to tackle issues concerning on-site ethanol recovery and still need to evaluate the suitability of the remaining residue as feed for cattle. Then there are potential problems in finding power station customers near SSF farms capable of using the bioethanol, together with a possible negative impact should the system expand to areas currently used to grow food for humans.

A paper detailing the research project has been published in the journal Biotechnology for Biofuels.