How different particle sizes of ground coffee influence the extraction of a good espresso coffee

Introduction: Espresso coffee (EC) is one of the most widely consumed beverages in the world and particularly in Italy. EC is different from other types of coffee, with its dense cream, mouthful flavor and attractive aroma [1]. This research aims to study the influence of ground coffee’s particle sizes on the EC extraction. Methods: Quantitative and qualitative analyses are carried out on the two most common coffee cultivars, Arabica and Robusta. Experiments with different averages of particle sizes (200-400 and 400-1000 microns) are performed through previously developed methods [2], in order to check optimal level of bioactive and volatile compounds at the end of the extraction. The samples are analyzed by GC-MS and HPLC-VWD. Results: EC extraction time, kinetics of extraction and its dependence on water pressure and temperature were controlled during the analyses. Bioactive compounds as caffeine, trigonelline, nicotinic acid, chlorogenic acids (CQAs) and volatiles were identified [3]. EC extractions were performed in duplicate for each particle size. Results confirmed a good extraction efficiency of caffeine, which accounted for 170 mg per cup at 200-400 microns and 90 mg at 400-1000 microns. Likewise, the amount of all other bioactive compounds increased when extracting coffee with smaller particle sizes. Conclusions: EC extraction at different particle sizes was evaluated by analyzing the content in bioactive components and volatiles that were found in EC. Extraction optimization will be enhanced by modifying extraction variables. References [1] C. Severini, I. Ricci, M. Marone, A. Derossi, and T.De Pilli, "Changes in the Aromatic Profile of Espresso Coffee as a Function of the Grinding Grade and Extraction Time: A Study by the Electronic Nose System," Agricultural and Food Chemistry, vol. 63, pp. 2321-2327, 2015. [2] Giovanni Caprioli, Manuela Cortese, Gloria Cristalli, Filippo Maggi, Luigi Odello, Massimo Ricciutelli, Gianni Sagratini, Veronica Sirocchi, Giacomo Tomassoni, Sauro Vittori, "Optimization of espresso machine parameters through the analysis of coffee odorants by HS-SPME-GC/MS," Food Chemistry, vol. 135, no. 3, pp. 1127-1133, 2012. [3] Jose A. Sanchez Lopez, Marco Wellinger, Alexia N. Gloess, Ralf Zimmermann, Chahan Yeretzian, "Extraction kinetics of coffee aroma compounds using a semi-automatic machine: On-line analysis by PTR-ToF-MS," International Journal of Mass Spectrometry, vol. xxx, pp. xxx-xxx, 2016