The secret to making stronger or weaker coffee depends on the firmness of the powder. The search for the perfect coffee recipe was the focus of a study, described in the journal Physics of Fluids, conducted by scientists at the University of Huddersfield.
The team, led by William Lee, used a mathematical model to identify the optimal mix that leads to the best taste of one of the world’s most popular beverages. Espresso, the experts explain, is prepared by grinding roasted coffee beans, which are then passed through a mixture of hot water at high pressure. This dissolves the soluble content of the beans and gives the drink its distinctive and unmistakable flavor.
In 2020, the research team found that more finely ground coffee beans are associated with a less intense taste. This counterintuitive result makes sense if one imagines parts of the blend where flavor extraction does not occur. To explore this hypothesis, experts divided the powder according to the consistency obtained from grinding. In the more compact blend, the scholars report, the water flowed faster and the coffee lost about 20-25 percent of its mass as the water passed through. In contrast, when the powder was less compact, the hot water passage was longer lasting, so the aroma was more intense.
“Our model,” says Lee, “shows that flow and aroma extraction tend to widen the disparity that depends on the compactness of the powder. This is a virtuous circle, because greater flow causes greater extraction, which consequently reduces resistance and leads to more intense flow.” The effect seems to persist until the mixture completely loses the percentage of soluble substances contained within it. These results, the authors comment, suggest that the taste of coffee depends directly on the level of aroma extraction.