Researchers at the University of Huddersfield discovered that finely ground coffee beans lead to weaker espresso due to uneven extraction during the brewing process. This finding stems from a mathematical model designed to analyze how fluid flow affects coffee extraction by dividing the coffee into two regions with distinct flow characteristics. As water is forced through the coffee bed at high pressure, it encounters uneven resistance, leading to variations in extraction rates. The model revealed that this uneven flow creates a feedback loop—where increased flow enhances extraction, which subsequently reduces resistance, thus perpetuating the cycle.
William Lee, a co-author of the study, noted that the uneven extraction can result in a coffee taste that is either underdeveloped or overly bitter, despite a seemingly adequate overall extraction level. The implications of this research suggest that better understanding and mitigating uneven extraction can improve espresso quality and promote more efficient coffee use, ultimately leading to cost savings. The researchers aim to refine their model for greater accuracy and explore practical changes to brewing methods to minimize uneven extraction. Their findings were published in the journal Physics of Fluids.
