Tuning the packed bed configuration for selective extraction of espresso non-volatiles based on polarity

Abstract

The taste of espresso is impacted by the absolute and relative concentrations of numerous marker compounds extracted during the brewing process. Due to the complex diffusion-convection process, the resulting concentration of the compounds in the espresso cup is largely influenced by the extraction conditions. In our previous work (Vaca Guerra et al., 2023) we have demonstrated that the hydrodynamics of extraction is significantly impacted by the size distribution of the coffee particles. In the present work, using a similar approach, we evaluated its impact on the kinetics of the extraction of specific coffee marker compounds. The results obtained show that, even having similar extraction conditions, changes in the bed configuration, namely reducing the specific wetting surface area, decreased the extraction rate of the components asymptotically. Moreover, being polar components the most affected and non-polar the least, the impact of particle size was correlated with the polarity of the components, showing good agreement. This work provides insight into the possible ways to perform selective extraction from components with different polarities driven only by variations of the initial bed parameters and evaluating the necessary conditions to scale up the results to larger bed lengths.