If coffee powder clumps together, the water does not adhere well to it and absorbs fewer flavourings. But there is a simple trick to prevent this.
Spectrum of science
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Cover image: Shutterstock / How intense an espresso tastes depends not on the origin of the beans or their price, but above all on the moisture they still contain.
The art of making outstanding coffee starts with grinding the beans. Because they become electrostatically charged, the powder sticks together and clumps. This impairs the flavour quality of the popular brew and both the grinder and coffee machine get dirty more quickly. What many a coffee lover may have already suspected has now been scientifically substantiated. A research team led by Joshua Méndez Harper from the University of Oregon has systematically investigated the phenomenon. And the scientists found out what can help: even a little moisture can minimise the electrostatic charge - and make the espresso more intense.
As the group reported in the specialist journal "Matter", electrostatically charged coffee powder is somewhat more difficult to wet with hot water, which means that fewer flavourings get into the espresso. However, if the beans are sprinkled with moisture before grinding, this can be prevented. Thanks to the conductive water, the electrical charges then flow away better. "It's not about the origin or the processing method. It's also not about the quality of the coffee or the price you pay for these beans," said Christopher Hendon, one of the researchers involved, told the New Scientist. "It depends on the roast level of the coffee and the humidity."
For their experiment, the researchers used a simple but effective measuring device: They placed a metal cup under a coffee grinder and connected an electrometer to it, which detected even small electrical charges. They then ground coffee beans of different origins, roasts and qualities. The friction and grinding caused the powder to become electrostatically charged - they measured between 0.1 and 100 nanocoulombs per gram of coffee. First author and volcanologist Joshua Méndez Harper compares the process in a press release to the eruption of a volcano: "During this process, the magma disintegrates into many small particles, which then emerge from the volcano in a large cloud. During this whole process, the particles rub against each other and become charged, creating lightning bolts." The extent to which the coffee powder becomes electrostatically charged during grinding depends on the roasting profile and - even more importantly - the moisture content of the beans. The effect was greatest with darker, drier beans.
The team then investigated whether the flavour of the espresso changed when the beans were moistened with a little water before grinding. The researchers found that the flavour intensity could be specifically controlled. Moister beans led to a longer extraction time and a stronger brew. In addition, the espresso shots tasted more similar to each other - a major hurdle for many baristas. They found that adding around 20 microlitres of water per gram of coffee, or around half a millilitre for a typical espresso, improved the taste and texture. According to Christopher Hendon, the findings could not only help people make better coffee at home, but also lead to savings of hundreds of millions of dollars. If the coffee beans in commercial coffee bars were moistened before grinding, more espresso could be brewed with fewer coffee beans - while maintaining the same intense flavour.
