Now coffee could get cars going too
Scientists have made biofuel from ground coffee produced in 20 different geographic regions - including caffeinated and decaffeinated forms.
New research from the University of Bath suggests waste coffee grounds could be a "sustainable fuel source" for powering vehicles.
The study found different varieties of coffee, including Robusta and Arabica, have reasonably standard composition and relevant physical properties of fuel.
This means all coffee waste could be a "viable" way of producing biodiesel, scientists from the University's Centre for Sustainable Chemical Technologies said.
Waste produced from the average coffee shop - around 22lb each day - was found to produce around two litres of biofuel.
Chris Chuck, Whorrod research fellow at the university, said the research highlighted the potential for waste coffee to be a "truly sustainable" biofuel.
"Around eight million tonnes of coffee are produced globally each year and ground waste coffee contains up to 20% oil per unit weight," Dr Chuck said.
"This oil also has similar properties to current feedstocks used to make biofuels. But, while those are cultivated specifically to produce fuel, spent coffee grounds are waste.
"Using these, there's a real potential to produce a truly sustainable second-generation biofuel."
Oil can be extracted from coffee grounds by soaking them in an organic solvent, before using a process called transesterification to transform them into biodiesel.
The University of Bath study examined how fuel properties depend on the type of coffee used. It found all waste coffee grounds has reasonably standard composition and relevant physical properties, irrespective of source.
"The yields and properties of biodiesel can differ depending on the growth conditions of current biodiesel feedstocks, sometimes causing them to fall out of specification," Dr Chuck added.
"The uniformity across the board for the coffee biodiesel fuel is good news for biofuel producers and users."
Dr Chuck added that coffee biodiesel would be a minor part of the energy mix but could be produced on a small scale by coffee shop chains to fuel vehicles used for deliveries.
The same delivery vehicles could be used to collect waste coffee grounds and take them to a central biodiesel production facility to be processed.
Companies such as London-based bio-bean already produce biodiesel and biomass pellets from waste coffee grounds.
Rhodri Jenkins, a PhD student in sustainable chemical technologies and first author of the study, said: " We estimate that a small coffee shop would produce around 10kg (22lb) of coffee waste per day, which could be used to produce around two litres of biofuel.
"There is also a large amount of waste produced by the coffee bean roasting industry, with defective beans being thrown away. If scaled up, we think coffee biodiesel has great potential as a sustainable fuel source."
The researchers are now examining whether other types of food waste can be used to make biofuels.
Effect Of The Type Of Bean, Processing, And Geographical Location On The Biodiesel Produced From Waste Coffee Grounds is published in Energy Fuels.