# Quantitative Analysis of Caffe in Roasted Coffee: A Comparison of Brewing Methods
## 3 Results and Discussion
### Brewing Methods
#### 3.3.2 Espresso  
The definition of Espresso encompasses three characteristics: prepared on demand, short extraction time (around 30 s), and use of pressure (around 9 bar). Water temperature is also essential and oscillates around 90 \({}^{\circ}\)C [67; 68]. Coffee prepared at various temperatures may exhibit differences in chemical composition [68; 69]; however, according to a study by [PERSON] et al. [70], coffee brewed at a lower temperature (83 \({}^{\circ}\)C) does not differ in taste from traditional coffee. A characteristic element of Espresso coffee is the layer of foam \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{6}{c}{**Brewing Parameters**} & \multicolumn{3}{c}{**Caffeine**} \\
**Brewing Time** & **T of Water** [\({}^{\circ}\)C] & **Amount** & **Amount** & **Coffee:Water** & **Determination** & **Caffeine Content** & **Reference** \\
**[h]** & **[\({}^{\circ}\)C]** & **[mL]** & **of Voice** [g] & **Ratio** & **Method** & **Confine Content** & **Reference** \\ \hline \hline  & & & & & & [mg/100 mL] & \\ \hline
4, 7 & 20 & 250 & 25 & 10:100 & HPLC & 125.00 & [30] \\ \hline
3 & 5 & & & & & 76.10 & \\
3 & 22 & & & & & 78.40 & \\
6 & 5 & & & & & 89.30 & \\
22 & & & & & & 97.30 & \\ \hline
16 & 20 & 30k & 1800 & 6:100 & HPLC & 72.00 & [23] \\ \hline
14 & 19 & 330 & 31.5 & 9:100 & HPLC & 75.05-80.50 & [34] \\ \hline
24 & 21–25 & 350 & 35 & 10:100 & HPLC & 108.00-118.00 & [39] \\ \hline
9 & 4 & 100 & 7 & 7:100 & HPLC & 63.00–95.00 & [40] \\ \hline
12 & 24 & 250 & 25 & 10:100 & HPLC & 96.30–120.40 & [44] \\ \hline
9 & & & & & & 48.87–66.60 & \\
24 & 23–25 & n.d. & n.d. & 5:100 & HPLC & 54.01–78.30 & [47] \\ \hline  & 5 & & & & & 116.60–120.10 (A) & \\  & 10 & & & & & 120.10–121.30 (A) & \\
15 & 15 & & & & & 125.20–125.70 (A) & [49] \\  & 5 & & & & & 175.3–180.10 (R) & \\  & 10 & & & & & 179.90–180.00 (R) & \\  & 15 & & & & & 178.60–178.80 (R) & \\ \hline
12 & 4 & & & & & 137.00 & \\
10 & 150 & 30 & 20:100 & HPLC & 135.00 & [59] \\ \hline
18 & 22 & n.d. & n.d. & 10:100 & HPLC & 48.00–49.00 & [60] \\ \hline  & & & & & & [mg/100 gl] & \\ \hline
24 & n.d. & 3000 & 450 & 15:100 & HPLC & 1288.00 & [29] \\ \hline
5, 16, 24 & 10 & n.d. & n.d. & 17–20:100 & HPLC & 761.00–1002.00 & [42] \\ \hline n.d. & 20 & n.d. & n.d. & 5–11:100 & SP & 2670.00 & [43] \\ \hline
24 & 19.3 & 5000 & 300 & 6:100 & HPLC & 605.00–743.00 & [57] \\ \hline
7, 15, 5, 24 & 4, 17, 30 & n.d. & n.d. & 6–16:100 & HPLC & 4080.76 & [58] \\ \hline \hline \end{tabular} Abbreviations: A—Arabica; n.d.—no data; HPLC—high-performance liquid chromatography; R—Robusta; SP—spectrophotometry; T—temperature.  
\end{table} 
Table 5: Cold brew method—brewing parameters and caffeine content. (crema) on the surface, which should represent 10% of the brew volume (25-30 mL), and its persistence and volume are also influenced by many factors [71; 72]. Espresso coffee was characterized by caffeine contents ranging from 47.30-1210.80 mg/100 mL to 457.00-6379.00 mg/100 g (Table 6). Despite using comparable brewing conditions, characterized by an average extraction time of 25.5 s, an average temperature of 92 \({}^{\circ}\)C, and pressure in the 9-20 bar range, significant differences in caffeine content were observed between the studies. With this method, even slight differences could have affected the results. An example is the study by [PERSON] et al. [50], in which the effect of water temperature (constant, increasing, and decreasing temperature gradient) on caffeine content was observed. Arabica coffee contained the highest content of this ingredient at constant water temperature. In the case of Robust coffee, an increasing temperature gradient increased caffeine extraction. Higher caffeine content was observed in three studies that reported results in volume-based units [34; 40; 45] and one study [35] that presented results in mass-based units.