The extraction process for coffee is complicated due to the nature of the coffee. In this paper, we studied the particle size distribution for coffee grinds and further analyzed that with the help of an inverted microscope and a scanning electron microscope. We drew a conclusion that the coffee grinds can be divided into two parts: cell fragments with smaller particles size and intact coffee cells with larger particles. The intact coffee cell was found to be a porous media. Therefore, we tried to brew the espresso with both normal grind size coffee and sieved coffee to study the extraction of the coffee as a function of the mass ratio of espresso collected. The high-performance liquid chromatography and mass spectrometry were performed to both espresso prepared by normal grind size coffee and sieved coffee mixed with glass beads. The results showed that the compounds extracted for both brews are mostly identical. We also tried to fit our data to a double porosity mathematical model that was recently published, and we found that the model is not perfect for our espresso brewing conditions.
Zhong, Sichen and Stork, Lauren Elizabeth, "Mass Transfer Effects of Particle Size on Brewing Espresso" (2017). Rose-Hulman Undergraduate Research Publications. 24.