The trick is to reduce the amount of static electricity generated when grinding whole coffee beans, which otherwise causes them to stick together and clog the grinder.
Funnily enough, coffee connoisseurs have long been spritzing the beans to hydrate them before grinding. Now scientists have confirmed that it really matters! The study showed how baristas can reduce static electricity to produce richer espresso.
A little about the research itself
Hendon, who previously showed how freezing coffee beans improves flavor, collaborated with former University of Oregon volcanologist Joshua Mendez Harper to investigate which types of coffee tend to clump and why, as well as how this affects brewing.
Harper, Hendon and their colleagues compared a set of commercially sourced and laboratory-roasted coffee beans that varied in origin, roasting time and moisture content. They measured the static electricity in each coffee after grinding, as well as the particle size of the freshly ground coffee and the taste of the finished drink.
Grinding whole coffee beans into small particles creates a lot of friction as the particles rub against each other and break apart. This generates static electricity – the separation of charged particles – in much the same way that dust particles in volcanic plumes rub against each other and discharge to form lightning.
By grinding coffee beans twice, the researchers showed that most of the static electricity in ground coffee comes from breaking down the beans and, to a lesser extent, from friction between them.
For bean types that tend to clump together when ground, the drier, darker roasts used in the team’s experiments produced more electrostatic charges than lighter roasts. Researchers suspect this may be because dark roasts are more fragile than lightly roasted beans, which retain moisture.
Comparing ground beans with and without added water, Harper and colleagues also showed that adding water before grinding resulted in longer espresso brew times and consistently stronger brews. The water penetrates the moistened coffee grounds and imparts more flavor to the less clumpy beans.
Speaking to New Scientist, Hendon recommends adding about 20ml of water per gram of coffee, or about half a ml for a regular shot of espresso, to improve its consistency and taste.