Researchers are already developing methods of making biofuel from cellulosic waste, such as corn stover and wood fibers, offering reduced environmental impact and no competition with food crops. Now, new research is investigating the possibility of turning waste from the winemaking industry into biofuel, not requiring the planting of any new crops.

This alternative is being explored by PhD student Kendall Corbin at the School of Agriculture, Food and Wine at the University of Adelaide, Australia. She analyzed the composition of grape marc, the term used to describe solid leftovers such as skins, seeds and stalks.

The research found that in dry weight, between 31 to 54 percent of grape marc consisted of carbohydrate. Of this total, between 47 and 80 percent was soluble in water.

Corbin looked at cabernet sauvignon and sauvignon blanc grapes. She also investigated how to pre-treat grape marc with acid and enzymes in order to boost efficiency.

Using acids and enzymes, a tonne (1.1 tons) of grape marc could be converted into up to 400 liters (106 US gal) of bioethanol. Without those additives, most of the carbohydrates found in grape marc could be converted directly to ethanol through fermentation, with a yield of up to 270 liters from that same amount. The remaining part could be used as fertilizer or animal feed.

"Using plant biomass for the production of liquid biofuels can be difficult because of it structurally complex nature that is not always easily broken down," says Corbin. "Grape marc is readily available, can be sourced cheaply and is rich in the type of carbohydrates that are easily fermented."

Details of the research are published in the journal Bioresource Technology.