Grinding coffee with a little water reduces static electricity and produces a heartier, more intense espresso: Study

The fracturing and friction of coffee beans during grinding generates electricity that causes the coffee particles to clump together and stick to the grinder. The researchers report December 6 in the journal Matter that coffee beans with higher internal humidity produce less static electricity, which means less wasted coffee and less mess to clean up.

This effect can be simulated by adding a small amount of water to the beans just before grinding them. The team also showed that grinding with a little water produces a heartier, more intense espresso.

“Moisture, whether residual moisture inside the roasted coffee or external moisture added during grinding, is what dictates the amount of filler formed during grinding,” explains l lead author Christopher Hendon, a computational materials chemist at the University of Oregon.

“Water not only reduces static electricity and therefore damage when grinding, but it can also have a major impact on the intensity of the drink and, potentially, the ability to access higher concentrations of flavors favorable.”

These improvements in coffee extraction could have massive economic implications for the coffee industry, which accounts for $343.2 billion, or 1.5 percent of the U.S. gross domestic product, according to researchers. “Increasing the concentration by 10-15% for the same mass of dry coffee has huge implications in terms of saving money and improving quality,” says Hendon.

The fact that coffee grinds produce static electricity has long been known in the coffee industry, where this electrification causes clumping and occasional zaps, but little is known about how different coffee attributes contribute to this phenomenon or its impact on brewing. To identify factors associated with the production of static electricity during coffee grinding, Hendon teamed up with volcanologists who study similar electrification processes during volcanic eruptions.

“During the eruption, the magma breaks into a multitude of small particles which then come out of the volcano in this large plume, and during this whole process, these particles rub against each other and charge each other to the point of producing lightning “, explains the first. author and volcanologist Joshua Méndez Harper of Portland State University. “In a simplistic way, it’s similar to coffee grinding, where you take these beans and grind them into a fine powder.”

The researchers measured the amount of static electricity produced when they ground different commercially and in-house roasted coffee beans, which varied depending on factors such as country of origin, processing method (natural, washed or decaffeinated), roast color and moisture content. They also compared the impact of grinding coarseness on the amount of electricity produced.

There was no association between static electricity and country of origin or coffee processing method, but the researchers found associations between electrification and water content, roast color, and particle size. Less electricity was produced when the coffee had a higher internal moisture content and when the coffee was ground at a coarser setting.

Light roasts produced less charge, and that charge was more likely to be positive, while darker roasts, which also tend to be drier, charged negatively and produced greater overall charge. Researchers also showed that dark roast coffees produce much finer particles than light roast coffees when ground at the same setting.

Next, the team tested whether grinding with water changed how the espresso was prepared. When they compared espresso made with identical coffee beans ground with or without a little water, they found that grinding with water resulted in a longer extraction time and a stronger brew. Grinding with water also made espressos more similar from shot to shot, overcoming a major obstacle for baristas and industrial coffee brewers.

Although they only tested espresso, the researchers say these benefits would apply to many other brewing methods. “The main material advantage of adding water during grinding is that you can pack the bed more densely because there is less clumping,” says Hendon.

“Espresso is the worst offender, but you’ll also see benefits in brewing formats where you pour water over the coffee or in small percolation systems like a stovetop Bialetti. Where you won’t see no advantage during brewing is for methods like the French press, where you submerge the coffee in water.

The researchers plan to continue their research into how to brew the perfect coffee. “Now that we know which grind settings to use to make reproducible espresso, we can begin to try to understand what factors give rise to sensory differences in coffee taste,” says Hendon.

Their work also has implications beyond everyday life, as the electrification of granular materials is an active area of ​​research in materials science, geophysics and engineering.

“It’s kind of like the beginning of a joke: a volcanologist and a coffee expert walk into a bar and come out with a newspaper,” says Méndez Harper, “but I think there are a lot more opportunities for this type of collaboration, and there is much more to know about how coffee breaks, how it flows as particles, and how it interacts with water. These investigations can help solve parallel problems in geophysics, whether it’s landslides, volcanic eruptions or how water seeps through the ground.