February 26, 2024

A Shot of Science: Perfecting Espresso Extraction for Maximum Flavor

Scientists discovered that more finely ground coffee beans result in weaker espresso due to unequal extraction. By comprehending and preventing uneven extraction, it might be possible to enhance coffee developing and accomplish monetary cost savings through more efficient coffee usage.
” This is essential because the taste of the coffee depends on the level of extraction,” said Lee. “Too little extraction and the taste of the coffee is what specialists call underdeveloped, or as I describe it: smoky water. Too much extraction and the coffee tastes extremely bitter.

Scientists discovered that more carefully ground coffee beans result in weaker espresso due to unequal extraction. They utilized a simple mathematical model to divide the coffee into two areas and taken a look at how uneven circulation impacts the brewing process. This unequal circulation continued throughout various parts of the coffee bed, impacting the taste of the coffee. By understanding and preventing unequal extraction, it may be possible to improve coffee developing and attain financial cost savings through more effective coffee use.
Understanding the origin of irregular extraction in brewing espresso can improve the beverage and make it possible for considerable financial cost savings by utilizing coffee more effectively and sustainably.
University of Huddersfield scientists discovered that unequal extraction in espresso brewing results in weaker coffee when using carefully ground beans. Understanding and preventing this phenomenon could enhance coffee taste and enable financial savings through more efficient coffee usage.
Espresso coffee is brewed by first grinding roasted coffee beans into grains. Hot water then forces its way through a bed of coffee grains at high pressure, and the soluble material of the coffee grains dissolves into the water (extraction) to produce espresso.

In 2020, scientists found that more carefully ground coffee beans brew a weaker espresso. This counterintuitive experimental outcome makes good sense if, for some factor, areas exist within the coffee bed where less and even no coffee is extracted. This uneven extraction becomes more pronounced when coffee is ground more finely.
In Physics of Fluids, from AIP Publishing, University of Huddersfield scientists explored the function of uneven coffee extraction utilizing an easy mathematical design. They split the coffee into 2 areas to examine whether uneven flow carries out in reality make weaker espresso.
In this figure, Q is the rate of flow, epsilon is the porosity (which increases as coffee is extracted), and c is the concentration of dissolved coffee (a procedure of the strength of the espresso). Credit: W.T. Lee, A. Smith, and A. Arshad
One of the regions in the model system hosted more securely packed coffee than the other, which triggered an initial disparity in flow resistance due to the fact that water streams faster through more tightly packed grains. The extraction of coffee decreased the circulation resistance even more, as coffee grains lose about 20% to 25% of their mass during the process.
” Our model shows that circulation and extraction broadened the initial variation in flow between the two areas due to a positive feedback loop, in which more flow leads to more extraction, which in turn decreases resistance and causes more flow,” stated co-author William Lee. “This effect appears to constantly be active, and it isnt until one of the areas has all of its soluble coffee extracted that we see the experimentally observed reduction in extraction with reducing grind size.”
The scientists were amazed to discover the model always anticipates uneven flow across different parts of the coffee bed.
” This is very important due to the fact that the taste of the coffee depends on the level of extraction,” said Lee. “Too little extraction and the taste of the coffee is what professionals call underdeveloped, or as I describe it: smoky water. Too much extraction and the coffee tastes really bitter. These results suggest that even if it looks like the total extraction is at the best level, it may be due to a mix of underdeveloped and bitter coffee.”
Comprehending the origin of unequal extraction and avoiding or preventing it might enable much better brews and substantial monetary savings by utilizing coffee more effectively.
” Our next step is to make the model more sensible to see if we can obtain more comprehensive insights into this confusing phenomenon,” stated Lee. “Once this is achieved, we can begin to consider whether it is possible to make modifications to the way espresso coffee is brewed to reduce the amount of irregular extraction.”
Recommendation: “Uneven extraction in coffee developing” by W. T. Lee, A. Smith and A. Arshad, 9 May 2023, Physics of Fluids.DOI: 10.1063/ 5.0138998.