The “perfect recipe” for espresso has a lot to do with the compact disc of ground coffee that is pressed into the machine’s filter holder, according to a new study.
An international team of mathematicians and environmental scientists believes they have taken a big step towards answering a very old question — and one that has already been echoed on several occasions: how to obtain the ideal espresso.
In a study published on April 1st (don’t worry, it’s not a lie) researchers argue that it is possible to calculate with mathematical rigor the ideal conditions for extracting great coffee. The key lies, above all, in the compact disc of ground coffee that is pressed into the machine’s filter holder.
When hot water passes through this block of coffee, it extracts compounds responsible for the flavor, color and caffeine, explains But the final result depends on several factors, such as the compaction of the coffee, the time of contact with the water and, mainly, the grain size of the grind.
Accurately predicting the impact of these variables has always been a difficult task — until now.
Researchers in this new study at Royal Society Open Science analyzed coffee beans of Rwandan and Colombian origin, ground to 11 different thicknesses, from very fine to coarser grinds. Each sample was placed in tubes and observed using three-dimensional imaging technology, X-ray microcomputed tomography, which allowed the creation of detailed maps of the internal structure of ground coffee, including the tiny spaces between the particles, invisible to the naked eye, through which water circulates.
Based on the models, the team digitally simulated the flow of water through the coffee using the so-called percolation theorya branch of physics that studies the movement of fluids in porous media. This was done with the aim of understanding the extent to which the internal channels formed between the grains facilitated a continuous flow of water along the machine’s disc.
Comparison between the different samples allowed the authors to develop an equation capable of calculating the permeability of ground coffee — the ease with which water passes through it. According to the researchers, the results coincide very solidly with the predictions of the physical theory used.
The study concludes that factors such as the connection between the pores, the size of the beans, the surface area and the way the coffee is compacted determine the contact time between the water and the coffee and, consequently, the intensity and complexity of the flavor. The greater this contact, the more intense the extraction tends to be.
The researchers believe that these formulas could be useful for improving machinery and equipment in the industry, and that they can lead to more precise adjustments in grinding, filtering and extraction.
Other studies point to other “secrets”, such as . Of course, outside the laboratory, there is still room for personal taste: whether the espresso tastes good to you is perhaps the most important criterion.
