THE IMPACT OF GROUND COFFEE PARTICLE SIZE ON THE EXTRACTION OF ESPRESSO COFFEE

Espresso coffee (EC) is one of the most known and consumed types of coffee. EC extraction depends deeply on ground coffee particles produced by the grinding process. To achieve a tempting aroma and taste in EC, the grinding process is in fact a crucial step, because the taste and flavor change a lot due to the particle size of ground coffee [1, 2]. Particle size distribution (PSD) is essential for extraction kinetics and hydrodynamics of the coffee packed bed [3]. The extraction yield and the strength of the extracted coffee depend greatly on PSD. The same type of roasted coffee in three different PSD (coarse, medium and fine) can generate from sour to acidic (non-volatiles) and from woody/papery to rubbery (volatiles) notes, while maintaining the temperature and pressure constant (94⁰C and 9 bar) [4, 5]. This highlights that the porosity of the bed and the particle size have to be adjusted to obtain the desired flavor. The influence of PSD on the number of volatiles and non-volatiles in extracted coffee has not well been studied yet [6, 7]. This research particularly aims to develop an innovative extraction process through PSD by decreasing the amount of grinded coffee before extraction (from 14 g to 12 g for double Italian EC, at particle sizes between 200-400 and 400-1000 microns). Quantitative and qualitative analyses on bioactive compounds (caffeine, trigonelline and CQAs) are carried out with HPLC-VWD and GC-MS [8]. Extraction are performed in triplicate for each particle size. The first results confirm a good extraction efficiency of caffeine, which accounted for 170 mg (200-400 microns) and 90 mg (400-1000 microns), respectively. Thus, the number of bioactive compounds increase by extracting with smaller particle size. The final outcomes will give us the opportunity to study further different extraction processes and to develop more sustainable and economically affordable coffee of high quality.