Solid waste left over from wine-making could make a competitive biofuel.
Up to 400 liters of bioethanol could end up produced by fermentation of a metric ton of grape marc (the leftover skins, stalks and seeds from wine-making).
Global wine production leaves an estimated 13 million metric tons of grape marc waste each year. Estimates show several hundred thousand metric tons end up generated annually and it is generally disposed of at a cost to the winery.
“This is a potentially economic use for what is largely a waste product,” said University of Adelaide Associate Professor Rachel Burton, program leader with the Australian Research Council (ARC) Centre of Excellence in Plant Cell Walls in the School of Agriculture, Food and Wine.
PhD candidate Kendall Corbin analyzed the composition of grape marc from two grape varieties, cabernet sauvignon and sauvignon blanc. She also investigated pre-treatment of the grape marc with acid and enzymes.
Corbin found the majority of the carbohydrates found in grape marc could end up converted directly to ethanol through fermentation with a yield of up to 270 liters per metric ton of grape marc. The leftover product was suitable for use as an animal feed or fertilizer.
Ethanol yields could end up increased by pre-treatment with acid and enzymes up to 400 liters a metric ton.
“Using plant biomass for the production of liquid biofuels can be difficult because of its structurally complex nature that is not always easily broken down,” Corbin said.
“Grape marc is readily available, can be sourced cheaply and is rich in the type of carbohydrates that are easily fermented,” she said.
“We’ve shown that there is a potential new industry with the evolution of local biofuel processing plants to add value to the grape for an environmentally friendly biofuel,” Burton said.