Influence of espresso machine parameters on coffee extraction.

Level of bioactive components and aroma profile of espresso coffee depend also on different espresso coffee machines, working with different mechanisms, and by extraction temperature and pressure set in the machine. The present contribution will report results of some years of research on such issue, studying electrical (Aurelia) and mechanical (Leva) pump equipped machine, along with different water temperature (88, 92 and 98 °C) and pressure (7, 9 and 11 bar) settings. The study on the effect of those variables has been used to assess the level, in different extraction conditions, of 10 chosen aroma constituents, chlorogenic acids (3-CQU, 5-CQA and 3,5-diCQA), caffeine, trigonelline and nicotinic acid. Influence of the main two cultivars, Arabica and Robusta, on the quantitative assay results were studied. More, the above analysis was applied to time portions of espresso coffee, prepared by collecting the portion of EC produced in the first 10 s, and then portions every 5 s, for a total of 7 fractions, to study the kinetics of extraction and its dependence on pressure, temperature and coffee blends used, during espresso making. Finally, the aroma sensory profile was studied, using a selected panel of trained sensory judges. Analytical instruments used for experiments were GC-MS for aroma constituents, and HPLC-DAD for the other molecules. Results demonstrated that the espresso machine settings for the best espresso coffee, as assessed by sensory panel, were 9 bar and 88 or 92 °C. The two different espresso machine showed a quite different extraction kinetic, with Leva machine being more efficient in the first fractions.