Physicists Present Findings From Study On Channeling – CoffeeTalk

Scientists from the University of Warsaw have discovered that “channeling” during the brewing process can lead to non-uniform filtration and lower extraction yield, which significantly affects the quality of the final brew. They presented their preliminary findings at the American Physical Society’s Global Physics Summit in Anaheim, California. The Specialty Coffee Association sets strict guidelines for brewing espresso, which include heating water to 92° to 95°C and forcing it through a bed of 7 to 9 grams of finely ground coffee for 20 to 30 seconds. However, most coffee shops don’t follow these guidelines closely, as brewing machines allow baristas to configure water pressure, temperature, and other key variables to their liking.

In 2020, Christopher Hendon’s lab at the University of Oregon helped devise a mathematical model for brewing the perfect cup of espresso over and over while minimizing waste. They focused on an easily measurable property known as the extraction yield (EY), which depends on controlling water flow and pressure as the liquid percolates through the coffee grounds. They concluded that the most reproducible thing to do is use fewer coffee beans and opt for a coarser grind with a bit less water; brew time was largely irrelevant.

Three years later, Hendon’s team showed that adding a single squirt of water to coffee beans before grinding can significantly reduce the static electric charge on the resulting grounds, reducing clumping during brewing, yielding less waste and the strong, consistent flow needed to produce a tasty cup of espresso. Good baristas already employ the water trick, known as the Ross droplet technique, but this was the first time scientists have rigorously tested that well-known hack and measured the actual charge on different types of coffee.

A team of physicists at the University of Warsaw in Poland has conducted a study on the mechanical and physical processes involved in brewing coffee. The team, led by Maciej Lisicki, a physicist, aims to understand the complex phenomenon of channeling, which is a reactive flow through a porous medium that undergoes dynamic reconfiguration. The team’s research is motivated by many myths or assumptions within the coffee community, as many people have a religious attitude towards their favorite drink.

The team initially tried to use a simple home coffee machine for their experiments but eventually partnered with Coffeelab, a major roaster in Poland, and CoffeeMachineSale, the largest global distributor of roasting gear. This brought industrial-grade equipment and professional coffee expertise to the project, including state-of-the-art grinders and a cafe-grade espresso machine equipped with a pressure sensor, flow meter, and scales. The entire setup was connected to laboratory laptops via a microchip and controlled with custom software that allowed the scientists to precisely monitor pressure, mass, and water flowing through the coffee.

The scientists measured the total dissolved solids to determine the rate at which coffee is dissolved, comparing brews without a channel to those with artificially induced channels. They found that channeling adversely affected extraction yields, but not the rate at which water flows through the espresso puck. This is due to the structural rearrangement of coffee grounds under pressure, which compacts and swells up when hit with water under high pressure.

The team is now factoring their results into numerical and theoretical models of porous bed extraction and compiling an atlas of different kinds of espresso pucks based on micro-CT imaging of the coffee. Their approach may help the coffee industry brew with more knowledge, as many people follow procedures based on unconfirmed intuitions or claims that prove to be true.

Read More @ Ars Technica