The epidermis of the coffee bean, known as coffee silverskin, is usually removed after the beans have been dried, and of course used coffee grounds are normally discarded unless people use them in their garden or as an abrasive cleaning product.

It might be time to reconsider putting them in a landfill, according to a study from the University of Granada which set out to see what other value they might have. They found that the antioxidant effects of these coffee grounds are 500 times greater than those found in vitamin C and could be employed to create functional foods with significant health benefits. 

Credit: UGR Divulga

"They also contain high levels of melanoidins, which are produced during the roasting process and give coffee its brown colour. The biological properties of these melanoidins could be harnessed for a range of practical applications, such as preventing harmful pathogens from growing in food products. If we are to harness the beneficial prebiotic effects of the coffee by-products, first of all we need to remove the melanoidins, since they interfere with such beneficial prebiotic properties,"  Professor José Ángel Rufíán Henares points out .

The researchers writing in Food Science and Technology conclude that processed coffee by-products could potentially be recycled as sources of new food ingredients. This would also greatly diminish the environmental impact of discarded coffee by-products.