Quantitative Analysis of Caffeine in Roasted Coffee: A Comparison of Brewing Methods
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Department of Dietetics, John Paul II University in Biała Podlaska, Sidorska 95/97, 21-500 Biała Podlaska, Poland
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Regional Research Centre on Environment, Agriculture and Innovative Technologies EKO-AGRO-TECH, John Paul II University in Biała Podlaska, Sidorska 95/97, 21-500 Biała Podlaska, Poland
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Authors to whom correspondence should be addressed.
Appl. Sci. 2024, 14(23), 11395; https://doi.org/10.3390/app142311395
Submission received: 8 November 2024
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Revised: 3 December 2024
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Accepted: 5 December 2024
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Published: 6 December 2024
(This article belongs to the Special Issue Characterization of Bioactive Compounds and Antioxidants in Natural Products)
Abstract
:Coffee is one of the most widely consumed beverages in the world due to its sensory and health benefits. The caffeine content, a bioactive compound of coffee, depends on many factors, including the brewing method, which is the subject of ongoing scientific research. In addition, various methods are used in studies to determine the caffeine content. However, it is worth noting that there is considerable variation in the individual analytical parameters within these methods. The aim of this study was to update the data on the effects of different brewing methods on the caffeine content of the brew and to present the current state of knowledge on techniques for the determination of this compound. A literature review was conducted, taking into account the latest studies in this field. The results showed that the caffeine content (mg/100 mL) of the brew prepared with the Cold Brew method was 48.50–179.95, Espresso—50.40–965.60, French Press—52.00–123.90, AeroPress—56.35–120.92, and Moka—128.00–539.90. These methods were characterized by different brewing parameters (time, water temperature and pressure, ratio of coffee to water), which differentiated the caffeine content. In addition, some methods were characterized by a wide range of caffeine content, suggesting that even minor variations in brewing method parameters may affect the content of this ingredient. High-performance liquid chromatography (HPLC) was the predominant method used. The detector wavelengths, along with other parameters of the HPLC method, such as gradient profiles and column temperatures, can affect the precision and accuracy of the analysis, and these differences can modify analyte retention and detection, leading to discrepancies in results. These results point to the need for studies that consider various brewing methods and a wide range of coffee types, including roast and origin, to accurately determine the effects of these factors on caffeine content determined by one precise method.
Keywords:
coffee; caffeine; HPLC; analytical methods; quantification; brewing methods; beverage; roasting degree; Arabica; Robusta1. Introduction
Coffee is one of the most consumed beverages in the world, and its production and consumption are steadily increasing. It is estimated that the world’s coffee consumption was 173.1 million bags (about 10.386 billion kilograms) in the years 2022/23 [1,2]. Furthermore, in 2022, coffee ranked as the 104th most traded commodity globally, accounting for approximately 0.19% of total world trade [3]. Coffee is characterized by its unique taste and intense aroma. In addition, it contains many valuable bioactive compounds: caffeine, chlorogenic acid, organic acids, melanoidins, and trigonelline, and due to the presence of these compounds, it can have a beneficial effect on human health [4,5,6]. Coffee consumption may reduce the risk of developing several chronic diseases, including hypertension (by 7%) [7], metabolic syndrome (by 13%) [8], type 2 diabetes (by 11%) [9], nonalcoholic fatty liver disease (by 29%) [10], chronic kidney disease (by 14%) [11], Alzheimer’s disease (by 32%) [12], liver cancer (by 35%) [13,14], oral and pharyngeal cancer (by 31%) [15], and death from various causes (by 7–12%), particularly gastrointestinal and cardiovascular diseases (by 22–59%) [16]. Studies have analyzed the mechanisms responsible for the beneficial effects of coffee on the human body and have suggested that one of them may be the reduction of oxidative stress and inflammation. A recent literature review confirmed that coffee consumption improves biomarkers for these processes in healthy individuals and those at increased risk of cardiovascular disease [17]. Similarly, the neuroprotective effects of coffee have been associated with a reduction in oxidative stress and inflammation [18]. The association between coffee consumption and the risk of developing chronic diseases and understanding the mechanisms of its beneficial effects require further research. The authors point out that it is crucial to analyze the effects of the individual coffee compounds, taking into account their potential synergistic effects. The variability of the chemical composition of coffee infusion remains a significant challenge [18].
Studies have shown that the beneficial effect depends on the number of cups of coffee consumed and may be related to caffeine content. Caffeine is a purine alkaloid with the chemical name 1,3,7-trimethylxanthine. It consists of a xanthine core (a purine derivative) with three methyl groups attached to nitrogen atoms at positions 1, 3, and 7. Caffeine is primarily absorbed in the small intestine, with absorption occurring within approximately 30–45 min. Caffeine metabolism occurs mainly in the liver by the enzyme CYP1A2, which belongs to the cytochrome P450 system. This process leads to the formation of the dimethylxanthines—paraxanthine, theobromine, and theophylline (Figure 1). These metabolites are then further degraded and removed from the body in the urine [4,19,20].
According to the European Food Safety Authority [21], daily caffeine intake from all sources for adults should not exceed 400 mg, while for pregnant and lactating women, it should not exceed 200 mg. Furthermore, the World Health Organization (WHO) recommends that pregnant women who exceed a daily intake of 300 mg of caffeine should reduce their consumption to minimize potential health risks [22]. There are no conclusive studies on the adverse effects of excessive caffeine consumption, which does not exclude the possibility of their occurrence [21,23]. Monitoring the content of this compound is important to prevent excessive consumption and minimize potential adverse health effects.
Coffee is a major source of caffeine in the diet due to its high alkaloid content compared to other beverages and products [21]. Several studies analyzed the impact of various factors, such as the degree of coffee bean roasting, on the content of bioactive compounds, aromatic profiles, volatile compounds, color, and structure [24,25,26]. The brewing method may have a particularly significant impact on the various factors influencing caffeine content. In recent years, a literature review was conducted on the effects of different brewing parameters on the caffeine content of green and black coffee [27]. The authors analyzed the influence of several factors, including brewing time, amount of coffee and water used, type of water, cup volume, brewing temperature, and pressure, as well as the type and variety of coffee, its origin, and the degrees of roasting or grinding of the beans. Although the literature review details the influence of individual brewing parameters, it does not consider the interaction between factors within a single brewing method. The conclusions point out that to reliably compare individual factors’ effects on caffeine content, other factors should remain constant. The review also takes into account certain limitations, such as the different ways of expressing the results, the various origins of the coffee, and the methods used to determine the caffeine content. In view of the above conclusions, it was decided to update and extend the state of the knowledge in this area. The aim of this review article was to analyze the effects of different brewing methods on the caffeine content of roasted coffee, taking into account the method of caffeine determination. Recalculated caffeine values focused on one type of coffee (roasted coffee) to reduce the variables influencing the results. It also presented the characteristics of coffee and brewing methods. In addition, different methods for determining caffeine (inter alia liquid chromatography, spectrophotometry) in coffee were considered, taking into account the analytical parameters used to present the current knowledge in this area and verify their impact on determining this component. As the health effects of caffeine are dose-dependent, it is necessary to consider as many factors as possible when comparing study results. This review attempts to address these variables comprehensively. The summary of the results of this study could have significant practical applications. First, analyzing the impact of different coffee brewing methods on caffeine content provides valuable insights that can help optimize brewing techniques. As a result, consumers will be able to make informed decisions on how to prepare coffee, potentially enhancing the health benefits of its consumption. Second, understanding the factors influencing caffeine levels in various brewing methods allows for refining the brewing process. Furthermore, the findings of this study could form the basis for developing health guidelines that establish safe and beneficial coffee consumption levels, customized to the needs of different social groups.
2. Methods
An article search was conducted in the electronic databases PubMed (https://pubmed.ncbi.nlm.nih.gov/, accessed on 5 July 2024) and Science Direct (https://www.sciencedirect.com/, accessed on 5 July 2024). Articles were searched by title and abstract, and the following keywords were used: coffee, caffeine, 1,3,7-trimethylxanthine, brewing methods, brewing process, making, extraction, preparation, and brew.
Original, peer-reviewed articles in English published between 2000 and 2024 were included in the review. Articles that contained a detailed description of the coffee brewing method and presented results on caffeine content were included in the analysis. Articles that were not related to the topic of the paper, duplicates, articles that were not available in the full version, and articles in which the name of the coffee preparation method was not specified were excluded from the analysis.
3. Results and Discussion
Initially, 529 articles were identified, and finally, 32 articles were included in the review. Figure 2 illustrates the search and article selection process [28].
The analysis considered the characteristics of the coffee, the method of caffeine determination, the parameters of the brewing process, and the caffeine content.
3.1. Coffee Characteristics
In many studies, only one type of coffee was analyzed. In Table 1, the characteristics of coffee based on geographic origin are presented.
There was a lack of information regarding the degree of roasting of the beans, and the origin varied, making it impossible to determine the precise effect of these factors on caffeine content. For the most part, Arabica coffee of varying roasting degrees, most often medium roast, from different countries, including Colombia, Brazil, Ethiopia, and Kenya, was used as study material.
3.2. Caffeine Determination Methods
The high-performance liquid chromatography (HPLC) method was the predominant technique for determining caffeine content and was used in 90.6% of the studies. Table 2 focuses on specific parameters of HPLC analysis without considering the caffeine content depending on the brewing method. Differences were demonstrated within a single determination method, which may also have influenced the variation in the obtained results besides the brewing technique and its parameters.
The Diode Array Detector (DAD) was used in more than a third of the studies (34.5%) in which the HPLC method was used, the Ultraviolet Detector in 27.6%, the Photodiode Array Detector (PDA) in 20.7% and the Variable Wavelength Detector in 10.4%. Two studies used the more advanced liquid chromatography method coupled with mass spectrometry [52,58]. DAD and PDA detectors were the most commonly employed due to their broad availability, cost-effectiveness, and the absence of ion suppression or significant matrix effects. Furthermore, these detectors allow for the simultaneous quantification of multiple compounds, although their analyte coverage remains more limited than that of mass spectrometers. The studies used a reversed-phase system with a C18 column (stationary phase of n-octadecylsilane molecules), except the Santanatoglia et al. [52], which used a Kinetex PFP (pentafluorophenyl stationary phase) column. Many studies (27.4%) used a classical column configuration (250 × 4.6 mm) to determine substances of medium polarity, such as caffeine. The remaining studies used shorter columns (150, 125, 100 mm) with different diameters (5.0, 4.0, 3.0. 2.7, 2.1 µm). The particle size of the stationary phase inside the column in 62.1% of the studies was 5 µm; in others, it was 2.6–4.0 µm. Only a few studies (20.7%) used a precolumn [30,31,32,51,53,57]. Caffeine was determined using a mobile phase containing different amounts of water and methanol. This method was used in most studies (69.0%), with modifications regarding the proportion between water and methanol. Only a few papers (31.0%) described HPLC methods using a water-acetonitrile mobile phase [30,31,32,41,45,47,49,58,59]. In almost all the studies, the mobile phase was modified by the addition of acids such as formic, acetic, phosphoric, and citric acids, except in the studies by Salamanca et al. [50], Kyroglou et al. [42], and Miłek et al. [46]. Gradient elution was used in 62.1% of the studies with varying gradient profiles. Sample injection volumes in the analyses ranged from 1 to 100 µL, with 10 µL (37.9%) and 20 µL (31.0%) being the most commonly used volumes. In most studies, the flow rate was 1 mL/min (41.4%), while 20.7% of studies used a flow rate of 0.4 mL/min. The remaining studies’ flow rate ranged from 0.2 to 1.5 mL/min. In 37.9% of the studies, no information was available about the column temperature used; in other studies, the authors mostly used the temperature 25 °C (24.1%) [29,36,37,38,42,44,56], and in others room temperature [30,31,32] or in the range (30–40 °C) [52,57,58,59]. Table 2 also includes the sample preparation step; in some studies, samples were filtered (65.5% of studies), centrifuged (37.9%), and diluted (34.5%) before HPLC analysis. Different wavelengths were used in the studies, as shown in Figure 3.
Table 3 shows the analytical method validation parameters such as coefficient of determination (R2), limit of detection, limit of quantification, and relative standard deviations.
Researchers obtained a high R2, exceeding 0.99, indicating the high precision and reliability of the measurement methods. However, there is limited information regarding other parameters—limit of detection, limit of quantification, and relative standard deviations. Only 27.6% of studies included these values [34,41,44,46,52,57,58].
Other studies used different methods for the determination of caffeine—spectrophotometry [43,46,54] and nuclear magnetic resonance (NMR) [35].
In the study by Santini et al. [54], coffee samples were diluted in pure water and then extracted three times with a chloroform solution. The organic phases were evaporated, and the remaining extract was dissolved in chloroform. Caffeine content was measured at 270 nm. In the study by Miłek et al. [46], the prepared coffee samples were filtered and then alkalinized with sodium hydroxide solution to pH 12.5–12.7. Then, caffeine extraction was carried out in two portions of chloroform, and the organic layer was collected and diluted with chloroform. Caffeine absorbance was measured at 276 nm. In the study by Kyroglou et al. [43], caffeine content was at 274 nm. All three methods were based on extracting caffeine from coffee samples with chloroform, spectrophotometric measurement of absorbance, and calculating caffeine content from a calibration curve. The main differences were the wavelength used for the measurement and the method of sample preparation and calibration.
In contrast, in a study by Ciaramelli et al. [35], coffee extracts were cold-dried and then dissolved in D2O to a concentration of 5–20 mg/mL, followed by sonication and centrifugation before NMR analysis. An internal standard was added to the supernatant, the pH of the samples was adjusted, and 1H NMR spectroscopy was performed using appropriate pulse sequences.
In turn, comparing the HPLC method to other methods of quantitative determination of caffeine, in the study by Miłek et al. [46], an HPLC method was used to determine caffeine content in addition to the spectrophotometric method. The caffeine content of coffee determined by the HPLC method was higher than the caffeine content determined spectrophotometrically. The authors indicated that the HPLC method is more advantageous as it allows faster analysis, minimizes analyte loss during sample preparation, and results are more accurate and reproducible.
In conclusion, the HPLC method is the most common method for determining caffeine in roasted coffee. Caffeine analysis in different studies using the HPLC method shows significant differences in the parameters and procedures used. Each parameter applied during the analysis may have significantly impacted the quantitative determination of caffeine, potentially influencing the accuracy and precision of the results. Future research should prioritize the standardization of methods to ensure greater comparability of results across studies. Consistent parameters such as mobile phase composition, detector types, and column configurations would help minimize inter-study variability. This approach would enhance understanding of how caffeine content correlates with the brewing method, coffee’s geographic origin, and other key characteristics.
3.3. Brewing Methods
Most of the studies included in the review analyzed brewing methods such as Cold Brew (50.0% of the eligible studies), Espresso (40.6%), French Press (28.1%), AeroPress (15.6%), and Moka (15.6%), (Table 4).
These studies also analyzed other coffee brewing methods, including American [33,38,54], Neapolitan [34,54], V60 [30,51,52,57], Pure Brew [51,52], Hot brew [43,47,59], Clever [51], Chemex [51]. Overflow methods predominated, with varying brewing parameters and caffeine content obtained. However, the limited number of studies makes it difficult to compare individual parameters and draw conclusions, so the remainder of this article focuses on the five most commonly used coffee brewing methods. Detailed results for each of these methods are presented below. The lack of information regarding the roasting degree and geographical origin of the coffee beans, which varied across studies, made it impossible to determine the impact of these factors on caffeine content accurately. Only 25.0% of the studies included coffee with at least two different roasting levels (light, medium, dark). It is worth noting that there was no standardized classification for roasting levels in the studies, and in some cases, terms such as “medium light” or “medium dark” were used. Furthermore, while some studies mentioned the roasting degree, they did not correlate this parameter with caffeine content results, nor were appropriate statistical analyses conducted, which further hindered the assessment of its influence on the outcomes. An interesting and clear example is the study by Santanatoglia et al. [52], where light-roasted coffee prepared using the French Press method contained higher caffeine content compared to coffee prepared with the AeroPress method. However, for medium and dark-roasted coffee, the results did not show statistically significant differences. Similarly, in the study by Santanatoglia et al. [53], espresso made from light and medium-roasted beans had higher caffeine content compared to dark-roasted coffee.
Regarding geographical origin, according to the data presented in Table 1, only some of the study materials came from the same region, but other parameters, such as roasting degree and brewing method, differed across studies. For this reason, it is not possible to conclusively attribute caffeine content to a specific geographical location. To accurately assess the impact of geographical origin on caffeine content, all variables that may influence the results, such as coffee species, roasting degree, and brewing method, must be considered. In the publications [34,36,37,43,60], the coffee originated from Colombia, and in most cases, it was the Arabica species [34,36,37,43], with a medium roast degree [36,37,43,60]. Despite this, the caffeine content varied among these samples— in studies [34,36,37], it was almost twice as high as in study [60]. However, the results of study [43] cannot be compared with the others due to the use of a different unit of measurement. This demonstrates that geographical origin is just one of many factors that can influence caffeine content.
In discussing the results, particular attention was paid to the effect of brewing parameters on caffeine content. Caffeine content was expressed in different units and was, therefore, converted to mg/100 mL or mg/100 g to facilitate comparison within the same unit. Although studies often report caffeine content per 100 g, it remains unclear whether this value refers to the weight of the brewed coffee or the coffee beans.
3.3.1. Cold Brew
Cold Brew represents an alternative coffee preparation method that is increasingly popular and accepted among consumers; however, a standardized definition has yet to be established [61,62,63]. The brewing process involves the prolonged immersion of coffee in cold water. Extraction should occur at lower than body temperature, usually at room temperature or 8 °C. The minimum extraction time depends on the temperature, with 2 h at 20 °C. Cold Brew coffee is traditionally extracted with water for 24 h [29]. The extraction of Cold Brew coffee is influenced by many factors such as coffee grade, roast and grind level, coffee-to-water ratio, temperatures, and water composition, as well as various mechanical processes (stirring, shaking, or use of ultrasonic waves) [62]. In the Cold Brew method, hot water is not used; therefore, microbiological contamination is possible [63]. High pressure during the brewing process [64] or thermal preservation [65] can reduce this risk while maintaining the quality of the beverage. The flavor profile of cold-brewed coffee differs from that of hot-brewed coffee, being fruitier and sweeter [66].
The caffeine content in coffee prepared using the Cold Brew method showed significant variability (Table 5). It ranged from 48.00 to 180.10 mg/100 mL in brew and from 605.00 to 4080.76 mg/100 g when expressed per 100 g of coffee. These values reflect distinct measurement approaches and are not directly comparable.
The effect of selected parameters on caffeine content was analyzed.
In the analyzed studies, the brewing time varied from 3 h to 24 h. Additional factors, such as pressure, were used in some studies to reduce the extraction time [42,43,60]. Higher caffeine content was recorded with longer brewing times [39,49]. Studies by Lapčíkova et al. [44] and Angeloni et al. [31] were conducted under similar conditions (same coffee species, identical coffee/water ratio, similar water temperature of 22–24 °C) but with different brewing times (3 h, 6 h or 12 h), confirmed this relationship.
In most studies, room-temperature water was used, as in the traditional method. Several studies analyzed the effect of changing water temperature on caffeine extraction [31,49,59]. It was observed that increasing the temperature from 5 °C to 22 °C increased the caffeine content for a 3 h extraction and higher for a 6 h brewing [31]. On the other hand, a study by Portela et al. [49] showed a similar relationship for the Arabica coffee species, but in the case of Robusta, as well as in the study by Zhai et al. [59], this parameter did not differentiate caffeine content.
The coffee-to-water ratio also proved to be a significant parameter affecting caffeine content. Muzykiewicz-Szymańska et al. [47] used a coffee-to-water ratio of 5:100, achieving twice the caffeine content of Fuller and Rao [39], who used a ratio of 10:100 under similar brewing time and temperature conditions. Additionally, a study by Zhai et al. [59] used a 20:100 ratio and reported higher caffeine contents in the mg/100 mL unit.
However, no clear correlations can be shown in studies where the results are presented in the unit mg/100 g due to variation or lack of information on some parameters [29,42,43,57,58].
These results suggest that extraction time, extraction temperature, and the ratio of coffee to water can significantly affect the caffeine content of a Cold Brew-prepared brew.
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 °C [67,68]. Coffee prepared at various temperatures may exhibit differences in chemical composition [68,69]; however, according to a study by Klotz et al. [70], coffee brewed at a lower temperature (83 °C) does not differ in taste from traditional coffee. A characteristic element of Espresso coffee is the layer of foam (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 °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 Salamanca 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 Robusta 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. Factors that may have influenced the results were a higher coffee-to-water ratio [45], higher water temperature [34], the use of a different method for caffeine determination [35], and the use of extraction accessories: filter baskets and perforated discs [41].
However, conducting a more detailed analysis of the effect of individual parameters on caffeine content is hampered by the incompleteness of the data in some studies. In many cases, the brewing time [33,38,41,45,48,55] or the amount of water used [30,41,53,55] is not provided, making it impossible to calculate the coffee-to-water ratio. The absence of this crucial information significantly limits the possibility of comparing studies. In contrast, the studies by Severini et al. [56] and Caprioli et al. [34] used similar parameters (water temperature and coffee-to-water ratio), but the lack of information on coffee type in one of the studies [56] makes it impossible to draw clear conclusions on the effect of brewing time on the caffeine content of the resulting espresso. The higher caffeine concentrations in the study by Caprioli et al. [34] may also be due to other factors, not only the coffee type. In one of these studies [55], the results were presented in mass units; therefore, the findings from this study should not be compared to those from the others.
The research on caffeine content in espresso coffee indicates the need to report all relevant variables to allow a systematic analysis of the influence of individual parameters while controlling for other factors.
3.3.3. French Press
The French Press method involves brewing coffee in a cylindrical vessel. The ground coffee is poured over hot water and left to brew for a few minutes. The filter plunger is then pushed down, causing the ground to fall to the bottom of the vessel. This method is considered to have the least environmental impact [73,74,75]. The resulting infusion is characterized by a medium color and cloudy appearance, with minimal or no foam due to sediment penetrating the piston mesh [76]. Extraction time can affect the resulting flavor, longer can increase bitterness and intensity, and shorter can emphasize acidity and sweetness [77].
In the French Press method, caffeine content oscillated between 52.00–148.52 mg/100 mL and 2971.02 mg/100 g (Table 7).
The similar values of caffeine content in the analyzed studies were due to the similarity of brewing conditions, characterized by an average extraction time of about 5 min and high water temperatures (90–98 °C).
Water temperature influenced caffeine extraction. Higher caffeine content was observed in studies using the highest water temperatures (98 °C and 95 °C, respectively) [31,39], while other studies using lower water temperatures reported values at similar levels. It should be noted that both of these studies [31,39] also used a higher coffee/water ratio, which may have further contributed to the increased caffeine extraction compared to the other studies analyzed.
The method of determination of caffeine content may also be an important factor influencing the results obtained. Studies by Santanatoglia et al. [51] and Santanatoglia et al. [52] conducted on the same coffee type and brewing parameters showed twice as high values using the high-performance liquid chromatography method compared to ultra-high-performance liquid chromatography. In addition, the coffees analyzed differed in origin, which could also have influenced the differences in results. In contrast, studies by Córdoba et al. [36] and Córdoba et al. [37], conducted under the same conditions and using the same method of determination, obtained similar results for the caffeine content of the brew.
Determining the factors contributing to the higher caffeine content reported in the study by Zakaria et al. [58] is challenging. This outcome may be attributed to using an alternative analytical technique and reporting results in units of mg/100 g, which complicates direct comparisons with other studies.
In summary, in the studies analyzed, brewing conditions were similar, resulting in caffeine contents at similar levels, and higher caffeine contents were recorded when longer brewing times, higher water temperatures, and higher coffee-to-water ratios were used.
3.3.4. AeroPress
The AeroPress method uses a device consisting of two cylinders—a smaller cylinder (equipped with an airtight seal placed inside), a larger cylinder, a piston, and a filter. Operates based on the principle of a syringe, utilizing manually generated pressure [78]. This method combines immersion and filtration techniques [77]. Coffee prepared using this method is characterized by high acidity, polyphenol content, and antioxidant potential [79]. Table 8 shows the range of caffeine content in coffee prepared using the AeroPress method, it ranged from 46.00 to 158.73 mg/100 mL. The brewing times were varied, with an average of 2 min.
The study by Santanatoglia et al. [51] used the longest extraction time among the studies analyzed and reported the highest caffeine content in the resulting brew. Similarly, the study by Angeloni et al. [30] used a longer brewing time than Lapčíková et al. [44], with the same other parameters, and obtained a higher caffeine content. These studies confirm that a longer brewing time may favor higher caffeine extraction. This observation is consistent with theoretical predictions regarding extraction kinetics, where increased contact time between the solvent (water) and the extracted material (coffee) leads to increased diffusion of soluble compounds, including caffeine.
The water temperatures used in the AeroPress method were the same (93 °C), except for one study where the temperature was 88 °C and one of the lowest caffeine values was recorded there [46].
The coffee-to-water ratio was similar in all studies, ranging from 6:100 to 7:100, so it can be assumed that this parameter did not significantly affect the variation in caffeine content.
The most significant influence on caffeine content may have been the brewing time in the AeroPress method, while the other parameters were similar.
3.3.5. Moka
Moka is one of the most popular coffee brewing methods in Italy [80]. This method uses low steam pressure, generated by heated water in an aluminum autoclave kettle, to move the water through the ground coffee in the filter, and the resulting brew is transported to the upper pot through suitable tubes [80,81,82]. The use of a high extraction temperature gives Moka coffee a harsh character. Many variables that are difficult to control also affect the brewing process of Moka coffee, which can lead to over-extraction. It is crucial to finish brewing when the first portions of water reach the top vessel, and the resulting brew is dark, syrupy, and creamy [77].
The caffeine content of coffee prepared using the Moka method was 128.0–539.90 mg/100 mL and 3194.00–6564.00 mg/100 g (Table 9).
In these studies, the brewing time ranged from 2 to 4 min, and the water was at low pressure and a temperature of 100 °C. Longer brewing time increased caffeine extraction [30,33,51]. However, the determination of this relationship is not precise due to the varying coffee-to-water ratio in all studies. In the study by Ciaramelli et al. [35], in which the brewing time was 10 min and the water temperature was lower (93 °C), a higher caffeine content was also observed. The longer brewing time allowed higher caffeine extraction from the coffee despite the lower water temperature.
Due to the few studies, no clear relationship can be observed in which a higher coffee–water ratio is correlated with higher caffeine content [30,33,35,51].
The comparative analysis of the results of studies on caffeine content in coffee requires special attention in the context of the analytical methods used. Significant discrepancies are observed in the determined caffeine concentrations depending on the analytical technique. The study in [54] showed significantly higher caffeine values using a spectroscopic method than studies using high-performance liquid chromatography. Similarly, the study of [35] showed extremely high caffeine concentrations using nuclear magnetic resonance spectroscopy.
The small number of studies and differences in the parameters and analytical methods analyzed prevented a direct comparison of the effects of individual brewing parameters on caffeine content.
3.4. Brewing Methods’ Comparison
This review compared the caffeine content of coffees prepared by different brewing methods: Cold Brew, Espresso, French Press, AeroPress, and Moka. Although the authors used the same brewing methods, the individual parameters within the method diverged. This resulted in a wide range of caffeine content within the brewing method, which made a clear comparison of the results impossible. A common feature across all brewing methods analyzed was a longer extraction time, increasing caffeine content. Furthermore, a similar relationship was observed in the Cold Brew and French Press methods, influenced by higher temperature and coffee-to-water ratio.
Figure 4 shows the range of caffeine content in coffees prepared with different brewing methods.
The analyzed brewing methods show considerable variation in the caffeine content of the brew. The Espresso and Moka had higher caffeine content than the other methods, possibly due to the higher coffee-to-water ratio and the pressure applied during brewing. In addition, in these methods, the coffee is in single contact with the water, which maximizes the concentration gradient between the two and leads to more efficient extraction. A high caffeine value can result from a combination of all these factors. In the case of the Cold Brew method, the extended brewing time promoted efficient caffeine extraction, but the low water temperature limited this process. The French Press and AeroPress methods had similar caffeine content due to similar brewing parameters (water temperature, coffee-to-water ratio). In addition to the parameters analyzed, caffeine content may have been influenced by other factors such as coffee grade, roasting degree, and origin. Moreover, the absence of information on coffee grade, roasting degree, origin, and other associated factors, including post-harvest processes, drying methods, and altitude of cultivation above sea level, makes it difficult to compare the results.
Furthermore, the HPLC method was mainly used in studies to determine caffeine. The parameters of this method, in particular different wavelengths, gradient profiles, and column temperatures, can affect the precision and accuracy of the analysis; these differences can modify the retention of the analyte and its detection, leading to discrepancies in the results.
An attempt was made to determine safe coffee consumption based on the available data. Considering the lowest caffeine content for each brewing method and the EFSA [21] recommendations (up to 400 mg/day), a daily intake of approximately four servings (200 mL) of Cold Brew coffee, three servings of French Press or AeroPress, one serving of Moka can be considered safe, provided no other sources of caffeine are consumed. In the case of Espresso, calculations suggest the possibility of consuming up to 26 servings (a standard 30 mL serving), but this should not be recommended and is unrealistic in practice due to consumption habits.
4. Conclusions
The review presents the characteristics of methods for determining caffeine and its content in roasted coffee prepared by different brewing methods, which has been the subject of numerous recent studies, especially in the last five years. The current state of knowledge in this field is discussed, considering as many factors as possible that affect the quantification of caffeine.
The analysis of the study showed that the predominant method for the determination of caffeine was the HPLC method, in which a variety of parameters could affect the accuracy of the determination. Different analytical approaches were used to obtain caffeine content results. However, it should be emphasized that methodological descriptions in future studies should include sufficient detail to enable interested readers to replicate the experiments and verify the accuracy of the data obtained. The analysis of these studies highlighted the importance of standardizing analytical methods and ways of reporting results in studies on caffeine content in coffee.
Accurate determination of caffeine content in coffee is important because of its beneficial effects on the body and the need to monitor excess due to potential adverse effects. The review revealed significant variability in caffeine content in coffee prepared using different brewing methods. Within a single brewing method, various parameters (such as brewing time, temperature, and coffee-to-water ratio) are applied, indicating that brewing techniques could be standardized.
The analysis demonstrated that coffee prepared using the AeroPress and French Press methods exhibited a lower range of caffeine content compared to other brewing methods. These methods may be considered when it is necessary to monitor dietary caffeine intake, for example, for pregnant or lactating women. On the other hand, other brewing methods, which showed higher caffeine content (e.g., Espresso and Moka), could be considered when higher caffeine intake is beneficial, such as in certain groups of athletes.
Time, temperature, coffee-to-water ratio, and pressure were crucial factors influencing caffeine extraction. However, many factors contributed to the difficulty in conclusively comparing results. This indicates the need for a comprehensive study considering the different brewing methods and a wide range of coffee types (including roast degree and origin) analyzed by one method to investigate all factors affecting caffeine content thoroughly.
Author Contributions
Conceptualization, I.M., A.D. and M.S.-S.; methodology, A.D. and M.S.-S.; writing—original draft preparation, A.D. and M.S.-S.; writing—review and editing, I.M.; visualization, A.D. and M.S.-S. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Conflicts of Interest
The authors declare no conflicts of interest.
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Figure 1.
The structure of caffeine and its main metabolites.
Figure 2.
Diagram of the search and selection process of articles included in the literature review. Source: based on Page et al. [28].
Figure 2.
Diagram of the search and selection process of articles included in the literature review. Source: based on Page et al. [28].
Figure 3.
Wavelengths used in the HPLC method to detect caffeine.
Figure 4.
Caffeine content in coffee by brewing method. (Results expressed in mg/100 mL to accurately reflect coffee consumption conditions. The interquartile range (IQR) was used to define a representative range for each brewing method).
Figure 4.
Caffeine content in coffee by brewing method. (Results expressed in mg/100 mL to accurately reflect coffee consumption conditions. The interquartile range (IQR) was used to define a representative range for each brewing method).
Table 1.
Coffee characteristics based on geographic origin.
| Authors | Type | Roasting Degree | Origin | ||||
|---|---|---|---|---|---|---|---|
| Arabica | Robusta | Blend | Light | Medium | Dark | ||
| [29] | ⏺ | n.d. | Brazil | ||||
| [30] | ⏺ | n.d. | Ethiopia | ||||
| [31] | ⏺ | n.d. | n.d. | ||||
| [32] | ⏺ | ⏺ | Ethiopia | ||||
| [33] | ⏺ | ⏺ | n.d. | ||||
| [34] | ⏺ | ⏺ | n.d. | Colombia | |||
| [35] | ⏺ | ⏺ | ⏺ | Colombia, Brazil, Burundi, Kenya, Guatemala, Tanzania, Uganda, Vietnam, India | |||
| [36] | ⏺ | ⏺ | Colombia | ||||
| [37] | ⏺ | ⏺ | Colombia | ||||
| [38] | n.d. | ⏺ | n.d. | ||||
| [39] | ⏺ | ⏺ | ⏺ | USA | |||
| [40] | n.d. | ⏺ | Brazil, Kenya, Colombia, Ethiopia, Aricha | ||||
| [41] | ⏺ | ⏺ | ⏺ | Central America, Indonesia | |||
| [42] | ⏺ | ⏺ | ⏺ | n.d. | |||
| [43] | ⏺ | ⏺ | Colombia | ||||
| [44] | ⏺ | ⏺ | ⏺ | Colombia, Costa Rica, Kenya, Ethiopia | |||
| [45] | ⏺ | ⏺ | ⏺ | ⏺ | n.d. | ||
| [46] | ⏺ | n.d. | Peru, Nicaragua | ||||
| [47] | ⏺ | ⏺ | ⏺ | ⏺ | Brazil, Colombia, India, Peru, Rwanda | ||
| [48] | ⏺ | n.d. | Croatia | ||||
| [49] | ⏺ | ⏺ | ⏺ | Brazil | |||
| [50] | ⏺ | ⏺ | ⏺ | n.d. | |||
| [51] | ⏺ | ⏺ | ⏺ | ⏺ | Ethiopia, Kenya | ||
| [52] | ⏺ | ⏺ | ⏺ | ⏺ | El Salvador, Uganda | ||
| [53] | ⏺ | ⏺ | ⏺ | ⏺ | Kenya | ||
| [54] | ⏺ | n.d. | n.d. | ||||
| [55] | ⏺ | n.d. | n.d. | ||||
| [56] | n.d. | n.d. | n.d. | ||||
| [57] | ⏺ | n.d. | El Salvador, Guatemala Bolivia, Brazil | ||||
| [58] | n.d. | n.d. | Jamaica | ||||
| [59] | ⏺ | n.d. | Brazil | ||||
| [60] | n.d. | ⏺ | Colombia | ||||
Abbreviations: n.d.—no data.
Table 2.
Parameters of methods for determining caffeine in roasted coffee.
| Reference | Method | Column | Mobile Phase | Elution | Injection [µL] | Flow Rate [mL/min] | Column T [°C] | Wavelength (nm) | Sample Preparation | Other Labeled Compounds |
|---|---|---|---|---|---|---|---|---|---|---|
| [29] | HPLC-DAD | C18—250 × 4.6 mm | water, methanol, acetic acid (79.9, 20.0, 0.1) | isocratic | 10 | 1.0 | 25 | 278 | filtered (0.45 µm filter) | – |
| [30] | HPLC-DAD | C18—150 × 3 mm, 2.7 μm precolumn of the same phase | formic acid, water (A), acetonitrile (B) | gradient, 0–24 min: from 95% A to 10% A | 5 | 0.4 | room | 278 | centrifuged (12,000 rpm, 5 min), diluted (1:10 with water) | CGAs |
| [31] | HPLC-DAD | C18—150 × 3 mm, 2.7 μm; precolumn of the same phase | formic acid, water (A), acetonitrile (B) | gradient, 0–5 min: 95% A 5–15 min: from 95% A to 56% A 15–17 min: from 56% A to 10% A 17–24 min: 10% A | 5 | 0.4 | room | 278 | centrifuged 12,074× g, 5 min), diluted (1:10 with water) | CGAs |
| [32] | HPLC-DAD | C18—150 × 3 mm, 2.7 μm; precolumn of the same phase | formic acid, water (A), acetonitrile (B) | gradient | 5 | 0.4 | room | 278 | diluted (1:10 with water) centrifuged (16,900× g, 5 min) | CGAs |
| [33] | HPLC-PDA | C18—250 × 4.6 mm, 4 μm | 3% formic acid (A), methanol (B) | gradient, 0–20 min: from 2% B to 32% B 20–30 min: from 32% B to 40% B 30–40 min: t from 40% B to 95% B 40–45 min: isocratic at 95% B | 20 | 1.0 | n.d. | 278 | filtered (0.45 μm filter) | – |
| [34] | HPLC-VWD | C18—250 × 3 mm, 5 μm | 0.3% formic acid, water (A), methanol (B) | gradient, 0 min: 25% B 0–10 min: from 25% B to 60% B 10–15 min: 60% B 15–20 min: from 60% B to 25% B 20–25 min: 25% B | 10 | 0.4 | n.d. | 270 | diluted (1:50 in the mobile phase) centrifuged (10,000 rpm, 10 min) filtered (0.45 μm filter) | nicotinic acid, trigonelline |
| [36] | HPLC-PDA | C18—250 × 4.6 mm, 5 μm | 1% acetic acid (A), methanol (B) | gradient, 0–8 min: 96% A, 4% B 8–20 min: 72% A, 28% B 20–28 min: 58% A, 42% B | 10 | 1.5 | 25 | 275 | n.d. | CQAs, trigonelline |
| [37] | HPLC-DAD (UV/VIS) | C18—250 × 4.6 mm, 5 μm | 1% acetic acid (A), methanol (B) | gradient, 0–8 min: 96% A, 4% B 8–20 min: 72% A, 28% B 20–28 min: 58% A, 42% B | 10 | 1.5 | 25 | 275 | n.d. | CQAs, trigonelline |
| [38] | HPLC-VWD | C18—125 × 4 mm, 5 μm | water, methanol, acetic acid (74.0, 25.0, 1.0) | isocratic | 20 | 0.9 | 25 | 254 | filtered (0.22 µm filter) | – |
| [39] | HPLC-DAD | C18—150 × 4.6 mm, 5 μm | 95% 2.0 mM phosphoric acid, 5% methanol (A), 95% methanol, 5% 2.0 mM phosphoric acid (B) | isocratic (75% A, 25% B) | 10 | 1.0 | 40 | 280 | dilution (1:4 with water), filtered (0.20 µm filter) added water | 3-chlorogenic acid |
| [40] | HPLC-UV | C18—250 × 4.6 mm, 5 μm | 10 mM citric acid (A), methanol (B) | gradient, 0–10 min: 85% A, 15% B 10–30 min: from 85% A, 15% B to 60% A, 40% B | 20 | 1.0 | n.d. | 276 | added Carrez reagents I, II and mixed, centrifuged (45,000× g, 10 min), filtered (0.45 μm filter) | CGAs—total |
| [41] | HPLC-VWD | C18—250 × 3 mm, 5 μm | phosphoric acid, water (A), acetonitrile (B) | gradient, 0–5 min: 2% B 5–10 min: from 2% B to 15% B 10–15 min: from 15% B to 20% B 15–20 min: from 20% B to 50% B 20–40 min: 100% B 40–50 min: from 100% B to 2% B | 5 | 0.4 | n.d. | 200 (for 10 min) after 240 (for the rest run time) | diluted (1:50 in mobile phase), centrifuged (13,000 rpm, 10 min) filtered (0.45 μm filter) | mix compounds (acetic acid, caffeic acid, caffeine, 5-caffeoylquinic acid, citric acid, malic acid, nicotinic acid, tartaric acid, and trigonelline) |
| [42] | HPLC-UV | C18—250 × 4 mm, 5 μm | water, methanol (80.0, 20.0) | isocratic, 10 min | 20 | 0.5 | 25 | 275 | n.d. | – |
| [44] | HPLC-UV/Vis | C18—150 × 4.6 mm, 2.6 μm | 0.05% phosphoric acid, water | isocratic, 54 min | 10 | 0.5 to 0.8 | 25 | 210 | filtered (0.20 μm filter) | chlorogenic acid |
| [45] | HPLC-PDA | Polar-RP—250 × 4.6 mm, 4 μm | 1% formic acid, water (A), acetonitrile (B) | gradient, 0–35 min: 5% B to 8% B | 100 | 1.0 | 40 | 280 | diluted (1:20 with water and methanol) centrifuged (16,200× g, 5 min) | CQAs—total |
| [46] | HPLC-DAD | C18— 250 × 4.6 mm, 5 μm | water, methanol (95.0, 5.0) | isocratic, 7 min | 10 | 1.0 | n.d. | 272 | n.d. | – |
| [47] | HPLC-UV | C18—125 × 4 mm, 5 μm | 0.5 M H3PO4 (pH 2.5), acetonitrile, methanol | isocratic | 20 | 1.0 | n.d. | 272 | filtered (papers filter) | – |
| [48] | HPLC-PDA | C18—250 × 4.6 mm, 5 μm | 3% formic acid (A), methanol (B) | gradient, 0–20 min: from 2% B to 32% B 20–30 min: from 32% B to 40% B 30–40 min: from 40% B to 95% B 40–45 min: 95% B | 20 | 1.0 | n.d. | 278 | filtered (0.45 μm filter) | phenolic compounds |
| [49] | HPLC-UV/Vis | C18—250 × 4.6 mm, 5 μm | 5% acetic acid (A), acetonitrile (B) | gradient, 0–5 min: 3% B 5–25 min: from 3% B to 20% B 27–30 min: 3% B | 20 | 1.0 | n.d. | 272 | filtered (0.45 μm filter) | CGAs—total |
| [50] | HPLC-UV | C18—100 × 4.6 mm, 5 μm | methanol, water (40.0, 60.0) | isocratic | 20 | 1.0 | n.d. | 270 | diluted, filtered (0.2 μm filter) | – |
| [51] | HPLC-DAD | C18—250 × 3.0 mm, 5 μm; precolumn C18—40 × 3.0 mm, 5 μm | 0.1% formic acid, water (A), 0.1% formic acid, methanol (B) | gradient | 3 | 0.8 | 40 | 270 | n.d. | CGAs |
| [52] | UHPLC-MS/MS | Kinetex PFP—100 × 2.1 mm, 2.6 μm | 0.1% formic acid, water (A), 0.1% formic acid, methanol (B) | gradient, 0–2 min: 20% B 2–15 min: 80% B 15–18 min: 80% B 18–23 min: 100% B 23–35 min: 20% B | 2 | 0.2 | 30 | - | centrifuged (15,000 rpm, 5 min), filtered | bioactive compounds (thirteen) |
| [53] | HPLC-DAD | C18—250 × 3.0 mm, 5 μm precolumn C18—40 × 3.0 mm, 5 μm | 0.1% formic acid, water (A), 0.1% formic acid, methanol (B) | gradient, 0–10 min: 20% B (isocratic) 10–15 min: 20% B to 35% B 15–20 min: 35% B to 55% B 20 min: 85% B (isocratic) 20–25 min: 85% B to 20% B | 3 | 0.8 | 40 | 270 | diluted (1:50), centrifuged (10,000 rpm, 5 min), filtered (0.45 μm filter) | CGAs, phenolic acids |
| [55] | HPLC-UV/Vis | C18—150 × 4.6 mm, 5 μm | 0.5% formic acid, water (A), 0.5% formic acid, methanol (B) | gradient, 0–1.2 min: 2% B 1.2–2.5 min: 2% B to 20% B 2.5–13 min: 20% B to 40% B 13–14.5 min: 40% B to 95% B 14.5–15 min: 95% B 15–21 min: 95% B to 2% B | 10 | 1.2 | n.d. | 272 | diluted (1:5–50), (filtered 0.2 μm filter), centrifuged (4700 rpm, 10 min) | trigonelline, 5-caffeoylquinic acid |
| [56] | HPLC-UV/Vis | C18—125 × 4 mm, 5 μm | water, methanol, acetic acid (74.0, 25.0,1.0) | isocratic | 20 | 0.9 | 25 | 254 | filtered (0.22 µm filter) | – |
| [57] | HPLC-PDA (UV/Vis) | C18—100 × 4.6 mm, 3.5 μm; guard column with similar composition | 0.1% formic acid, water (A), methanol (B) | gradient, 0–12 min: 85% A, 15% B | 1 | 1.0 | 30 | 272 | n.d. | CGAs, gallic acid, trigonelline, furfural 5-(hydroxymethyl)furfural |
| [58] | LC-ESI-MS/MS | C18—100 × 2.1 mm, 2.6 μm | acetonitrile (A), 0.1% formic acid (B) | gradient, 0–10 min: 10% A, 90% B | 10 | 0.5 | 35 | – | filtered (0.22 μm filter) | phenolic compounds |
| [59] | HPLC-DAD | C18—250 × 4.6 mm | 0.1% phosphoric acid, water (A), acetonitrile (B) | isocratic, 90% A, 10% B | 10 | 1.0 | 30 | 272 | filtered (paper filter) | – |
| [60] | HPLC-PDA | C18—250 × 4.6 mm, 5 μm | 10 mM citric acid, water (A), methanol (B) | isocratic, 40 min, 75% A, 25% B | 10 | 0.4 | n.d. | 273 | diluted (1:20 with water), filtered (0.22 µm filter) | CGAs—total |
Abbreviations: C18—octadecylsilane column; CGAs—chlorogenic acids; CQAs—caffeoylquinic acids; DAD—Diode Array Detector; HPLC—high-performance liquid chromatography; LC–ESI–MS/MS—liquid chromatography-electrospray ionization tandem mass spectrometry; n.d.—no data; PDA—Photodiode Array Detector; PFP—pentafluorophenyl; RP—Reverse Phase; T—temperature; UHPLC-MS/MS—ultra-high performance liquid chromatography-tandem mass spectrometry; UV—Ultraviolet; UV-Vis—Ultraviolet-Visible; VWD—Variable Wavelength Detector.
Table 3.
Validation parameters for the high-performance liquid chromatography method.
| Reference | R2 | LOQ | LOD | RSD (%) | Other Parameters/Information |
|---|---|---|---|---|---|
| [29] | n.d. | n.d. | n.d. | n.d. | 5-point calibration curve (calibration range: 20–100 ppm) |
| [30] | 0.9994 | n.d. | n.d. | n.d. | 6-point calibration curve (calibration range: 0–0.632 μg) |
| [31] | 0.999 | n.d. | n.d. | n.d. | 6-point calibration curve |
| [32] | 0.9993 | n.d. | n.d. | n.d. | 6-point calibration curve (calibration range: 0–0.7575 μg) |
| [33] | n.d. | n.d. | n.d. | n.d. | external caffeine standard |
| [34] | >0.9985 | 0.1–0.2 mg/L | 0.03–0.06 mg/L | 0.74–4.44% | 5-point calibration curve (calibration range 10, 20, 50, 100, 250 mg/L) |
| [36] | >0.994 | n.d. | n.d. | n.d. | external caffeine standard |
| [37] | n.d. | n.d. | n.d. | n.d. | external caffeine standard |
| [38] | n.d. | n.d. | n.d. | n.d. | external caffeine standard |
| [39] | n.d. | n.d. | n.d. | n.d. | external caffeine standard |
| [40] | n.d. | n.d. | n.d. | n.d. | external caffeine standard |
| [41] | 0.9963 | 0.3 mg/L | 0.10 mg/L | 1.54–2.47% | 5-point calibration curve (calibration range: 5, 10, 25, 50, 100 mg/L) |
| [42] | n.d. | n.d. | n.d. | n.d. | n.d. |
| [44] | 0.9994 | 0.8134 μg/mL | 0.2684 μg/mL | calibration range: 0.225–1.125 mg/mL; y = 1217.2x − 2.5241 | |
| [45] | 0.9999 | n.d. | n.d. | n.d. | calibration range: 20–1000 ng |
| [46] | 0.9881 | 2 μg/mL | 0.5 μg/mL | n.d. | calibration range: 0.0625–1 mg; y = 18,940x + 944.19 |
| [47] | 0.999 | n.d. | n.d. | n.d. | y = 370,683x + 32.205 |
| [48] | n.d. | n.d. | n.d. | n.d. | external caffeine standard |
| [49] | ≥0.999 | n.d. | n.d. | n.d. | 5-point calibration curve (calibration range: 10–35 μg/mL) |
| [50] | n.d. | n.d. | n.d. | external caffeine standard | |
| [51] | n.d. | n.d. | n.d. | n.d. | n.d. |
| [52] | 1.000 | 0.004 μg/mL | 0.001 μg/mL | interday 4.00%; intraday 0.40% | calibration range: 0.005–5 µg/mL; y = 135,892x + 1311.1 |
| [53] | 0.9992 | 1.75 mg/L | 0.52 mg/L | interday 0.22%; intraday 1.46% | calibration range: 50–1000 mg/L; y = 1.509x − 6.93 |
| [54] | n.d. | n.d. | n.d. | n.d. | 5-point calibration curve |
| [56] | n.d. | n.d. | n.d. | n.d. | external caffeine standard |
| [57] | >0.99 | 151.0 mg/100 g | 45.0 mg/100 g | n.d. | 5/8-point calibration curve (calibration range: 23–117 mg/100 g); y = 1.6474x − 1.2918 |
| [58] | 0.9978 | 0.35 µg/mL | 0.10 µg/mL | interday: 0.35% | linear range: 0.0195−10 µg/mL; y = 10,373 x + 985.93 |
| [58] | n.d. | n.d. | n.d. | n.d. | 5-point calibration curve |
| [60] | n.d. | n.d. | n.d. | n.d. | external caffeine standard |
Abbreviations: LOD—limit of detection; LOQ—limit of quantification; n.d.—no data; R2—coefficient of determination; RSD—relative standard deviations.
Table 4.
Articles included in the review with consideration of the coffee brewing methods used.
| Authors | Cold Brew | Espresso | French Press | AeroPress | Moka |
|---|---|---|---|---|---|
| [29] | ⏺ | ⏺ | |||
| [30] | ⏺ | ⏺ | ⏺ | ⏺ | ⏺ |
| [31] | ⏺ | ||||
| [32] | ⏺ | ||||
| [33] | ⏺ | ⏺ | |||
| [34] | ⏺ | ||||
| [35] | ⏺ | ⏺ | |||
| [36] | ⏺ | ⏺ | |||
| [37] | ⏺ | ||||
| [38] | ⏺ | ||||
| [39] | ⏺ | ⏺ | |||
| [40] | ⏺ | ||||
| [41] | ⏺ | ||||
| [42] | ⏺ | ||||
| [43] | ⏺ | ||||
| [44] | ⏺ | ⏺ | ⏺ | ⏺ | |
| [45] | ⏺ | ||||
| [46] | ⏺ | ||||
| [47] | ⏺ | ||||
| [48] | ⏺ | ||||
| [49] | ⏺ | ||||
| [50] | ⏺ | ||||
| [51] | ⏺ | ⏺ | ⏺ | ||
| [52] | ⏺ | ⏺ | |||
| [53] | ⏺ | ||||
| [54] | ⏺ | ||||
| [55] | ⏺ | ||||
| [56] | ⏺ | ||||
| [57] | ⏺ | ||||
| [58] | ⏺ | ⏺ | |||
| [59] | ⏺ | ||||
| [60] | ⏺ |
Abbreviations: ⏺—denotes the specific brewing methods applied in this study.
Table 5.
Cold brew method—brewing parameters and caffeine content.
| Brewing Parameters | Caffeine Determination Method | Caffeine Content | Reference | |||||
|---|---|---|---|---|---|---|---|---|
| Brewing Time [h] | T of Water [°C] | Amount of Water [mL] | Amount of Coffee [g] | Coffee:Water Ratio | ||||
| [mg/100 mL] | ||||||||
| 4, 7 | 20 | 250 | 25 | 10:100 | HPLC | 125.00 | [30] | |
| 3 | 5 | 250 | 25 | 10:100 | HPLC | 76.10 | [31] | |
| 22 | 78.40 | |||||||
| 6 | 5 | 89.30 | ||||||
| 22 | 97.30 | |||||||
| 16 | 20 | 30k | 1800 | 6:100 | HPLC | 72.00 | [23] | |
| 14 | 19 | 330 | 31.5 | 9:100 | HPLC | 75.05–80.50 | [34] | |
| 24 | 21–25 | 350 | 35 | 10:100 | HPLC | 108.00–118.00 | [39] | |
| 9 | 4 | 100 | 7 | 7:100 | HPLC | 63.00–95.00 | [40] | |
| 12 | 24 | 250 | 25 | 10:100 | HPLC | 96.30–120.40 | [44] | |
| 9 | 23–25 | n.d. | n.d. | 5:100 | HPLC | 48.87–66.60 | [47] | |
| 24 | 54.01–78.30 | |||||||
| 15 | 5 | 150 | 15 | 10:100 | HPLC | 116.60–120.10 (A) | [49] | |
| 10 | 120.10–121.30 (A) | |||||||
| 15 | 122.50–125.70 (A) | |||||||
| 5 | 175.3–180.10 (R) | |||||||
| 10 | 179.90–180.00 (R) | |||||||
| 15 | 178.60–178.80 (R) | |||||||
| 12 | 4 | 150 | 30 | 20:100 | HPLC | 137.00 | [59] | |
| 10 | 135.00 | |||||||
| 18 | 22 | n.d. | n.d. | 10:100 | HPLC | 48.00–49.00 | [60] | |
| [mg/100 g] | ||||||||
| 24 | n.d. | 3000 | 450 | 15:100 | HPLC | 1288.00 | [29] | |
| 5, 16, 24 | 10 | n.d. | n.d. | 17–20:100 | HPLC | 761.00–1002.00 | [42] | |
| n.d. | 20 | n.d. | n.d. | 5–11:100 | SP | 2670.00 | [43] | |
| 24 | 19.3 | 5000 | 300 | 6:100 | HPLC | 605.00–743.00 | [57] | |
| 7, 15.5, 24 | 4, 17, 30 | n.d. | n.d. | 6–16:100 | HPLC | 4080.76 | [58] | |
Abbreviations: A—Arabica; n.d.—no data; HPLC—high-performance liquid chromatography; R—Robusta; SP—spectrophotometry; T—temperature.
Table 6.
Espresso method—brewing parameters and caffeine content.
| Brewing Parameters | Caffeine Determination Method | Caffeine Content | Reference | ||||
|---|---|---|---|---|---|---|---|
| Brewing Time [s] | T of Water [°C] | Amount of Water [mL] | Amount of Coffee [g] | Coffee:Water Ratio | |||
| [mg/100 mL] | |||||||
| 27 | 93 | n.d. | 14 | n.d. | HPLC | 410.00 | [30] |
| n.d. | 93 | 25 | 7 | 28:100 | HPLC | 244.00 | [33] |
| 25 | 92 | 25 | 7.5 | 28:100 | HPLC | 526.80–576.00 (A) | [34] |
| 911.20–1020.00 (R) | |||||||
| n.d. | 92 | 25 | 7 | 28:100 | HPLC | 248.68 | [38] |
| n.d. | 93 | n.d. | 14 | 50:100 | HPLC | 311.30–576.60 (A) | [41] |
| 505.70–1210.80 (R) | |||||||
| 30 | 90 | 25 | 7 | 28:100 | HPLC | 47.30–53.50 | [44] |
| n.d. | 92 | 15–53 | 9, 18 | n.d. | HPLC | 240.00–700.00 | [45] |
| n.d. | 95–97 | 50 | 7 | 14:100 | HPLC | 97.71 | [48] |
| 25 | 88–93 | 25 | 15 | 60–100 | HPLC | 174.00 (A) | [50] |
| 90 | 256.00 (A) | ||||||
| 93–88 | 214.00 (A) | ||||||
| 88–93 | 281.00 (R) | ||||||
| 90 | 245.00 (R) | ||||||
| 93–88 | 119.00 (R) | ||||||
| 25–26 | 93 | n.d. | 8 | n.d. | HPLC | 83.90–108.00 | [53] |
| 8–24 | 92 | 25 | 6, 7, 8 | 24–32:100 | HPLC | 320.12–521.44 | [56] |
| [mg/100 g] | |||||||
| 30 | 90 | 50 | 14 | 28:100 | NMR | 2868.00–3871.00 (A) | [35] |
| 4835.00–6379.00 (R) | |||||||
| n.d. | 79.1–96.5 | n.d. | 20 | n.d. | HPLC | 457.00 | [55] |
Abbreviations: A—Arabica; n.d.—no data; HPLC—high-performance liquid chromatography; NMR—nuclear magnetic resonance spectroscopy; R—Robusta; SP—spectrophotometry; T—temperature.
Table 7.
French press method—brewing parameters and caffeine content.
| Brewing Parameters | Caffeine Determination Method | Caffeine Content | Reference | ||||
|---|---|---|---|---|---|---|---|
| Brewing Time [min] | T of Water [°C] | Amount of Water [mL] | Amount of Coffee [g] | Coffee:Water Ratio | |||
| [mg/100 mL] | |||||||
| 5.00 | 93 | 250 | 15 | 6:100 | HPLC | 52.00 | [30] |
| 5.00 | 95 | 250 | 25 | 10:100 | HPLC | 109.40 | [31] |
| 5.00 | 90 | 330 | 31.5 | 9:100 | HPLC | 82.87–85.24 | [36] |
| 5.00 | 90 | 250 | 22.5 | 9:100 | HPLC | 82.00 | [37] |
| 6.00 | 98 | 350 | 35 | 10:100 | HPLC | 104.00–106.00 | [39] |
| 8.00 | 93 | 250 | 15 | 6:100 | HPLC | 55.40–77.0 | [44] |
| 4.00 | 93 | 300 | 20 | 7:100 | HPLC | 99.28–148.52 | [51] |
| 4.00 | 93 | 300 | 20 | 7:100 | UHPLC | 52.66–73.47 | [52] |
| [mg/100 g] | |||||||
| 6.00 | 93 | 660 | 36 | 5:100 | LC–ESI–MS/MS | 2971.02 | [58] |
Abbreviations: HPLC—high-performance liquid chromatography; LC–ESI–MS/MS—liquid chromatography-electrospray ionization tandem mass spectrometry; T—temperature; UHPLC—ultra-high-performance liquid chromatography.
Table 8.
AeroPress method—brewing parameters and caffeine content.
| Brewing Parameters | Caffeine Determination Method | Caffeine Content [mg/100 mL] | Reference | ||||
|---|---|---|---|---|---|---|---|
| Brewing Time [min] | T of Water [°C] | Amount of Water [mL] | Amount of Coffee [g] | Coffee:Water Ratio | |||
| 1.35 | 93 | 250 | 16.5 | 7:100 | HPLC | 78.00 | [30] |
| 1.25 | 93 | 250 | 18 | 7:100 | HPLC | 49.80–62.90 | [44] |
| 1.67 | 88 | 200 | 12 | 6:100 | HPLC | 46.00–75.00 | [46] |
| 3.75 | 93 | 225 | 15 | 7:100 | HPLC | 83.10–158.73 | [51] |
| 2.00 | 93 | 300 | 20 | 7:100 | UHPLC | 52.05–60.77 | [52] |
Abbreviations: HPLC—high-performance liquid chromatography; T—temperature; UHPLC—ultra-high-performance liquid chromatography.
Table 9.
Moka method—brewing parameters and caffeine content.
| Brewing Parameters | Caffeine Determination Method | Caffeine Content | Reference | ||||
|---|---|---|---|---|---|---|---|
| Brewing Time [min] | T of Water [°C] | Amount of Water [mL] | Amount of Coffee [g] | Coffee:Water Ratio | |||
| [mg/100 mL] | |||||||
| 2.13 | 100 | 150 | 15 | 10:100 | HPLC | 128.00 | [31] |
| 3.00 | 100 | 80 | 11.3 | 15:100 | HPLC | 168.00 | [33] |
| 3.67–4.00 | 100 | 250 | 20 | 8:100 | HPLC | 234.23–290.31 | [51] |
| n.d. | n.d. | n.d. | 10 | n.d. | SP | 539.90 | [54] |
| [mg/100 g] | |||||||
| 10.00 | 93 | 100 | 12 | 12:100 | NMR | 3194.00–4476.00 (A) | [35] |
| 4657.00–6564.00 (R) | |||||||
Abbreviations: A—Arabica; n.d.—no data; HPLC—high-performance liquid chromatography; NMR—nuclear magnetic resonance spectroscopy; R—Robusta; SP—spectrophotometer; T—temperature.
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Mystkowska, I.; Dmitrowicz, A.; Sijko-Szpańska, M. Quantitative Analysis of Caffeine in Roasted Coffee: A Comparison of Brewing Methods. Appl. Sci. 2024, 14, 11395. https://doi.org/10.3390/app142311395
AMA Style
Mystkowska I, Dmitrowicz A, Sijko-Szpańska M. Quantitative Analysis of Caffeine in Roasted Coffee: A Comparison of Brewing Methods. Applied Sciences. 2024; 14(23):11395. https://doi.org/10.3390/app142311395
Chicago/Turabian StyleMystkowska, Iwona, Aleksandra Dmitrowicz, and Monika Sijko-Szpańska. 2024. "Quantitative Analysis of Caffeine in Roasted Coffee: A Comparison of Brewing Methods" Applied Sciences 14, no. 23: 11395. https://doi.org/10.3390/app142311395
APA StyleMystkowska, I., Dmitrowicz, A., & Sijko-Szpańska, M. (2024). Quantitative Analysis of Caffeine in Roasted Coffee: A Comparison of Brewing Methods. Applied Sciences, 14(23), 11395. https://doi.org/10.3390/app142311395
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