The secret to obtaining a tastier espresso lies in making the coffee extraction process from the pressed powder of the beans uniform: this is demonstrated by a mathematical model which for the first time reveals the reason why ground that is too fine worsens the yield. The study results, which could help improve the product by limiting waste, are published in the journal Physics of Fluids by the University of Huddersfield in the UK.
The researchers used a mathematical model to try to understand whether the more finely ground powder worsens the quality of the coffee because it favors non-homogeneous extraction. In particular, they simulated what happens in the espresso machine filter when there is one area where the coffee powder is pressed more compactly than in the other. This initial disparity in the resistance to the flow of boiling water becomes even more accentuated due to the effect of the passage of the water and the extraction process itself, which further reduce the resistance to the flow (given that the coffee grains lose 20-25 % of their mass). This creates a vicious circle, where more water flow increases extraction which, in turn, reduces drag and increases flow even more.
“This is important because the taste of coffee depends on the level of extraction,” explains one of the authors of the study, William Lee. Too little extraction makes the coffee tasteless, while excessive extraction makes it bitter. “These results indicate that even if the overall extraction is at the right level, it could be a mix between coffee with an underdeveloped taste and bitter coffee.”
Source: Ansa
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