Coffee aficionados often add a drop of water to their beans before grinding – now scientists have shown that this leads to less mess and a more flavourful espresso
By Alex Wilkins
6 December 2023
A splash of water helps ground coffee avoid clumping together
D.Kvasnetskyy/Shutterstock
Adding a drop of water to your coffee beans before grinding them can reduce mess and lead to a more flavourful brew.
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Coffee aficionados often add a little water to their beans before grinding, either from a wet spoon or as a spritz of moisture, because it stops coffee grounds sticking together and keeps them from flying away from the main pile. Scientists think this is because the water reduces static electricity, but the exact mechanism and the perfect amount of water to add were unclear.
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To investigate, Christopher Hendon at the University of Oregon and his colleagues sprayed various amounts of water on a range of coffee beans that had been roasted for different lengths of time, with varying levels of internal moisture, and then put them through a grinder. They then measured the amount of static electricity, how large the ground coffee particles were and the flavour of the coffee brewed with an espresso machine.
They found that the most important factor in determining the electrostatic charge, and so the clumpiness of the coffee, was the total moisture in the beans before grinding. Beans roasted to a darker colour have less moisture, and this makes them more susceptible to clumping.
“It’s not about the origin or the processing method. It’s not about the quality of the coffee or the price that one might pay for those particular beans,” says Hendon. “It really boils down to the colour of coffee and the internal moisture.”