When preparing espresso coffee, various factors can affect the final taste of the drink and even the caffeine concentration, such as the water pressure, the grind size of the grains, the degree of compaction and the amount of coffee in grams. The good news is that science is revealing the mysteries of this complex process gradually begins to air.
With the help of mathematical models, scientists from various research centers have already observed that the secret of a good espresso does not lie in the excessively fine grinding of the grain, as we will see below. Coarser grinds also have numerous advantages.
What is the ideal grind for the perfect espresso?
Among the studies demonstrating an ideal grind for espresso is the study developed by an international team of scientists including members from the University of Oregon in the United States and the University of Limerick in Ireland.
This 2020 study, published in Matter magazine, examined what variables affect beverage quality even before ground coffee comes into contact with water and the extraction process begins.
For the group, the focus is on grinding, as it determines the size of the coffee grounds particles and therefore the surface area of the extraction process. In addition, particle size plays an important role in controlling surface permeability and flow rate when the coffee is already compacted in the machine’s filter.
The weird thing is that for a long time it was thought that finer grinds were better for espresso. However, the mathematical model developed by the team showed the opposite. At a certain point, a very fine grind will no longer allow for a homogeneous extraction, resulting in poor reproducibility, potentially undesirable results and wasted raw material.
“A barista is able to get a highly reproducible espresso with the same EY [rendimento de extração] “With 20 g of espresso, the coffee mass is reduced to 15 g and the coffee is ground much coarser, which is counterintuitive,” according to the authors of the study. The average extraction time in this case is about 15 seconds.
Why is the finer grind better?
Considering that the contact area of finer coffee is larger, the main hypothesis to justify the fact that espresso is “weaker” is that for some reason there are “regions” in the ground coffee mass where less or nothing of what we define as “coffee” is made.
After a detailed analysis, the idea becomes more plausible since coffee is not a single substance as we speak and think. In fact, around 2,000 different compounds are extracted from mud. They also break down during the grinding process and, depending on where they end up in the machine’s filter, can affect the taste.
Further studies on the preparation of espresso coffee
However, a group of scientists from the University of Huddersfield in England were not satisfied with the results or the first explanations of the ideal grind for espresso coffee. The latest study, published in the journal Physics of Fluids in March this year, involves the creation of another mathematical model to study the problem of overmilling.
According to the authors, the new results confirm previous research. “Surprisingly, the observed trend of a peak in extraction yield could be reproduced with grind size,” the article states. In other words, if the powder is very fine, the coffee extraction is not homogeneous and therefore the final quality of the drink can vary greatly.
Guilherme Lee, one of the authors of the study, reinforces this point of view, noting that the taste of coffee always depends on the degree of extraction. With low extraction, the coffee taste is more like “smoked water”. On the other hand, overextraction is characterized by a bitter taste.
“Our next step is to make the model [matemático] “It’s more realistic to see if we can get more detailed information about this puzzling phenomenon,” Lee said in a statement. Then “we can think about whether it’s possible to change the way espresso is made to reduce uneven extraction,” he concludes.
Source: Matter, Physics of Fluids and AIP