Reusing wastes generated by roasting coffee

There is no shortage of caffeine dealers in Australia. With each churning out hundreds of coffee shots every day, that’s a lot of leftover grounds! Having spent years studying the reuse of organic waste, we knew there was a better place for them than the local tip.

Working with Core Roasters, who make some of the most fragrant roasts in Melbourne, to reuse coffee grounds, spent filters and waste chaff (skins of coffee beans discarded during roasting), we discovered how richness in these wastes could be returned to earth.

The fragrant beans which make up our espressos and cappuccinos leave a byproduct which is quite dense in its make up. The spent coffee grounds provide a concentrated source of nutrients which can be great for your garden, if released properly.

Spent grounds can be spread liberally across soil and will eventually break down to a point where their goodness is released back into the earth. It will take time, so to speed up the transfer, we need to look after the microbes that unlock the goodness.

Much like humans, a well-balanced diet is important for microbes to do their best work. Coffee grounds are highly concentrated nutrient sources, so it's important to mix them up with other organic matter to better distribute their bounty. Through compost trials, a coffee waste composite (of two lots of chaff and one of spent grounds and filters) was found to have the nutritional balance that ensures every nutrient makes its way back into the soil - a simple way to deal with roasters’ waste.

Compost microbes do better on a diet of diverse wastes, so avoid feeding them the same composite all the time. For the home coffee drinkers, try including coffee grounds with kitchen scraps, and use the controlled environment of a gravity fed compost system (like Bioverter) to unlock the goodness in kitchen waste for your garden.

So don't throw away your grounds! There is a much better use for them, right under your feet.

Preparing a balanced coffee waste composite.