# Computer Percolation Models for Espresso Coffee: State of the Art, Results and Future Perspectives
## 3 Results and Discussion
### Results of Chemical Analyses
#### 3.1.1 Total Solids and Total Lipids: Results  
Total solids, also called dry matter, measure the strength or concentration of coffee brew, which is the first indicator of coffee extraction efficiency [10]. In this study, total solids have been calculated in different EC samples prepared by varying granulometry, pressure and temperature using two coffee types, i.e., Arabica and Robusta. These results are shown in Table 2.  
ECs prepared with finer coffee powder generate higher levels of total solids (total solids average of all ECs prepared with coarse, optimal and fine granulometry, 9.52, 9.82 and 10.73 g/100 mL for Arabica and 9.83, 10.44 and 11.46 g/100 mL for Robusta, respectively). At optimal conditions, i.e., 9 bar of pressure and 93.4 \({}^{\circ}\)C of water temperature set up for these coffee types, finer particle sizes increased the total solids level both for Arabica (8.79, 10.03 and 10.73 g/100 mL) and Robusta (9.46, 9.78 and 12.55 g/100 mL). These findings are in agreement with [32; 33; 34], in which higher total solids levels are reported when finer particles are used. On the other hand, the influence of water temperature and pressure is more complex to understand since variations were in ranges quite narrow. Similar results were found in another research project [17], which analysed different ECs prepared by varying pressure, temperature and tamping pressure and they concluded that among different extraction conditions variations, although slight, such differences in the EC cup are appreciable. Some variations are appreciable in our experiment as well. For example, \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Arabica** & **TS** & **RSD** & **Robusta** & **TS** & **RSD** \\
**Sample** & **(g/100 mL)** & **(\%)** & **Sample** & **(g/100 mL)** & **(\%)** \\ \hline A1 & 10.03 & 2.9 & R1 & 9.78 & 17.9 \\ A2 & 9.65 & 2.6 & R2 & 10.12 & 16.9 \\ A3 & 10.42 & 1.0 & R3 & 10.15 & 18.8 \\ A4 & 9.69 & 4.7 & R4 & 10.31 & 9.7 \\ A5 & 9.59 & 2.4 & R5 & 10.72 & 9.1 \\ A6 & 9.94 & 5.4 & R6 & 11.20 & 0.9 \\ A7 & 9.87 & 10.7 & R7 & 11.19 & 3.8 \\ A8 & 9.80 & 3.2 & R8 & 9.63 & 14 \\ A9 & 9.38 & 1.9 & R9 & 10.88 & 3.7 \\ A10 & 9.57 & 0.4 & R10 & 12.09 & 16.9 \\ A11 & 10.21 & 4.5 & R11 & 9.83 & 14.5 \\ A12 & 8.79 & 2.2 & R12 & 9.46 & 3.6 \\ A13 & 10.08 & 11.2 & R13 & 8.62 & 17.1 \\ A14 & 10.38 & 14.4 & R14 & 10.86 & 0.7 \\ A15 & 9.15 & 8.9 & R15 & 9.69 & 4.7 \\ A16 & 9.38 & 0.9 & R16 & 11.03 & 5.6 \\ A17 & 9.49 & 4.5 & R17 & 9.13 & 2.7 \\ A18 & 9.59 & 6.8 & R18 & 9.53 & 1.8 \\ A19 & 9.05 & 1.2 & R19 & 8.85 & 19.4 \\ A20 & 9.79 & 0.9 & R20 & 11.30 & 8.0 \\ A21 & 8.80 & 6.4 & R21 & 10.88 & 11.0 \\ A22 & 9.22 & 1.2 & R22 & 8.53 & 9.6 \\ A23 & 10.73 & 5.0 & R23 & 12.55 & 3.5 \\ A24 & 10.84 & 7.6 & R24 & 10.05 & 18.3 \\ A25 & 10.50 & 2.3 & R25 & 11.95 & 6.7 \\ A26 & 10.90 & 9.9 & R26 & 11.63 & 18.6 \\ A27 & 11.61 & 2.3 & R27 & 11.28 & 3.1 \\ A28 & 10.93 & 3.5 & R28 & 10.36 & 3.5 \\ A29 & 10.87 & 6.2 & R29 & 12.37 & 8.3 \\ A30 & 10.65 & 0.6 & R30 & 11.23 & 0.3 \\ A31 & 11.52 & 5.6 & R31 & 11.73 & 13.7 \\ A32 & 11.42 & 4.5 & R32 & 10.90 & 13.8 \\ A33 & 10.31 & 1.9 & R33 & 11.19 & 3.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Content of total solids (TS) (g/100 mL) found in different EC samples, Arabica and Robusta. ECs extracted with 93.4 \({}^{\circ}\)C generate a smaller increment on total solids than 88 \({}^{\circ}\)C and 98 \({}^{\circ}\)C especially with optimal granulometry and pressure in Arabica samples. Regardless of the water temperature used, in Arabica coffee increasing the water pressure results in higher total solids levels on coffees prepared with optimal granulometry whereas in lower total solid contents on ECs prepared with finer particles. Hence, particle sizes, water pressure and temperature can affect the total solids content and therefore the coffee extraction efficiency. The lipids in EC possess an important role in retaining lipophilic aroma compounds; therefore, high amount of lipids increases the aroma contained in the cup. Moreover, lipids can influence the foam phase [35].