Time-resolved extraction of caffeine and trigonelline from finely-ground espresso coffee with varying particle sizes and tamping pressures

We investigated the extraction kinetics of caffeine and trigonelline from espresso coffee prepared in a commercial machine under realistic process conditions with varying particle sizes and tamping pressures of the coffee powder. On the one hand, it was found that the particle size significantly affects the extraction kinetics with smaller particles leading to a higher extracted amount of caffeine and trigonelline per collected coffee mass. Tamping pressure, on the other hand, has no detectable effect. Furthermore, the total extracted coffee mass was found to influence coffee composition as measured by the trigonelline/caffeine ratio. All data were sampled in triplicates with a high time resolution using a newly constructed sampling device. Finally, we introduced a new reduced model that describes the measured data well and contains only physically meaningful parameters. This work provides detailed data for better understanding the extraction of nonvolatile water-soluble components from espresso coffee, thereby aiding model development and validation. The presented simplified model may also prove useful for other related applications.