Exploring the Impact of Various Manual Brewing Techniques on the Physicochemical and Sensory Characteristics of Brewed Coffee

Coffee cultivation in Indonesia primarily revolves around Arabica and Robusta. Liberica, a less-cultivated variety, often thrives in agroforestry systems, contributing to ecosystem preservation and biodiversity support. Exploration of coffee holds the potential to benefit farmers, coffee-related industries, and conservation initiatives. As a beverage product, coffee can have unique physical, chemical, and sensory characteristics influenced by various factors from farm to cup. Among these factors, brewing plays a crucial role. This study aims to determine the effects of popular manual brewing techniques (V60, French Press, and Vietnam Drip) on the physicochemical and sensory characteristics of Arabica and Liberica coffee. The study was conducted using a nested design. The analyses included pH, total dissolved solids, color parameters L* (brightness), IC50 and sensory evaluation by trained panelists. The results highlight that the different manual brewing techniques significantly affected the physicochemical and sensory characteristics of the brewed coffee. Interestingly, the effect of the brewing techniques was more pronounced in Arabica compared to Liberica coffee.


Introduction
Coffee is an important commodity that contributes to the world economy and the livelihoods of smallholder farmers and communities.The consumption of coffee increases every year.In 2022, global coffee consumption increased 3.3% to reach 170.3 million bags compared to the previous year [1].This surge in global coffee consumption has direct impact on Indonesia as the fourth largest producer and exporter country, with a total coffee production of 794.8 thousand tons in 2022 [1].
Today, coffee producers face unprecedented challenges, largely due to the spectre of climate change, which threatens the sustainability and availability of coffee.Reports indicate that land suitability for coffee cultivation has, in some cases, decreased [2].Although certain higher altitude regions may experience an increase in production suitability [3], the ramifications of climate change on coffee have far-reaching implications for both farmers and consumers [4] .
Among different coffee species, Coffea arabica (Arabica), C. canephora (Robusta), C. liberica (Liberica) and C. excelsa (Excelsa) are cultivated in Indonesia.C. arabica and C. canephora, the major species grown worldwide, are highly sensitive to shifts in climatic conditions.Consequently, the yield and quality of Arabica and Robusta coffee decline when the plants are not grown within their optimum temperature and conditions [5].C. liberica, a less-cultivated coffee species, primarily thrives in agroforestry systems, making significant contributions to ecosystem support and biodiversity conservation.Currently, C. liberica has garnered attention due to its resilience in coping with climate change and extreme conditions [6].
In addition to concerns about coffee production, there is growing awareness of the vulnerability of coffee quality to climate change [7].Coffee profiles can vary significantly due to multiple factors within the coffee production chain, from farm to cup [8].The quality of coffee as a beverage product is intricately tied to the processing of cherries into green beans, roasted coffees, and the brewing and serving process.An essential aspect of translating the flavors from coffee beans into the cup is the brewing process, making it a crucial subject for investigation.
Manual brewing techniques have gained popularity in recent times, prompting a surge in research on these methods.Each manual brewing technique comes with distinct protocols that may yield variations in the characteristics of the brewed coffee [8].Despite previous research on coffee brewing, there remains a gap in the study comparing the lesser-cultivated Liberica coffee with the majorly cultivated Arabica coffee.This study aims to examine the influence of different manual brewing techniques on the physicochemical and sensory profiles of Arabica and Liberica Coffee.

Materials
Samples of green Arabica and Liberica coffee beans (naturally processed) were obtained from Ijen Geopark area in Banyuwangi, Indonesia.Green coffee beans were roasted to a medium level using a W1A Giesen coffee roaster.

Sample Preparation
The roasted coffee beans were ground using a commercial coffee grinder and brewed using V60, French Press, and Vietnam Drip techiques following protocols used by Sunarharum et al, [8], Specialty Coffee Association [9], and Varady et al. [10].Those three techniques were selected because of their popularity.The protocols for manual brewing are given in Table 1.

Physical Analysis
pH was analysed using a hand-held digital pH meter, total dissolved solids (TDS) were analysed using a VST lab coffee refractometer, and color was analysed using a Konica Minolta color reader.

Chemical Analysis
Caffeine and antioxidant content was analysed following the methods used by Sunarharum et al. [11].

Sensory Analysis
Sensory analysis was conducted using the Quantitative Descriptive Analysis (QDA) method employing 8 trained panelists.The procedure includes selection and training of panelists, development of terms, sensory evaluation, data analysis, and interpretation of the results [12].To score the sensory attributes of the samples, unstructured 0-15 line scales with 0.5 increments were used.The evaluation covered 23 sensory attributes including aroma (jackfruit, spicy, chocolate, caramel, fermented, smoky), flavor (smoky, roasty, chocolate, caramel, spicy, jackfruit, dried fruit, fermented, black tea, earthy), taste (sweet, bitter, sour), aftertaste (bitter, sweet, astringent), and body.

Physicochemical Characteristics of Roasted Arabica and Liberica Coffee Beans
Before being used for brewing, medium-roasted Arabica and Liberica coffee beans were physicochemically characterized.The results of the analysis (Table 2) showed that the roasted Arabica and Liberica coffee beans contain ~1% caffeine.Both Arabica and Liberica exhibited strong antioxidant activities, with IC50 values between 0-50 ppm (note: a smaller IC50 value signifies a stronger antioxidative ability to inhibit free radicals [4]).The antioxidant activity of roasted Liberica coffee beans was higher than that of Arabica.A previous study by Saw et al. (2015) also found that Liberica coffee exhibits a higher antioxidant activity compared to Arabica.The antioxidants in coffee consist of phenols and non-phenolic compounds, all of which are considered part of plant defense system [13].Because antioxidants are known to buffer reactive oxygen species that accumulates during environmental stresses [14], the higher antioxidant activity in Liberica coffee is thought to correlate with its ability to withstand conditions arising from climate change.The pH value for Liberika was slightly higher than that of Arabica.This difference in pH value may be attributed to variations in the composition of the acids, which according to Pereira et al, [15] may include chlorogenic acid, quinic acid, malat acid, acetic acid, oxalic acid, formic acid, citric acid, and phosphoric acid.In addition, these compositional distinctions may also be influenced by factors related 1299 (2024) 012011 IOP Publishing doi:10.1088/1755-1315/1299/1/0120114 to coffee cultivation, such as growing conditions [5], as well as the processing and preparation methods, such as roasting [16].

Physicochemical Characteristics of Arabica and Liberica Coffee Brew
The roasted coffee samples were manually brewed using V60, French Press, and Vietnam Drip and then analysed to determine their physicochemical characteristics.The results of the analysis are given in Table 3. Table 3 Based on the results in Table 3, it is evident that Arabica and Liberica coffee, when brewed using different techniques, exhibit significant differences in terms of their antioxidant activity, pH, TDS, and brightness (L*).All three techniques resulted in coffee brew with high antioxidant activity (Liberica exhibited higher antioxidant activity than Arabica).The V60 brewing technique, interestingly, yielded coffee brew with the highest antioxidant activity for both Arabica and Liberica.The antioxidant activity in coffee is known to be influenced by various compounds, such as flavonoids and polyphenols, each characterized by distinct structure and heat stability.The use of hot water and longer extraction times during the brewing process can impact the extraction rate and can trigger chemical changes in these antioxidative compounds.Most importantly, the extraction efficiency of these compounds is mainly driven by their solubility in water [17].
In terms of pH, variations were observed among the brewed coffee samples, with the most pronounced difference occurring between the V60 and the other two techniques.The V60 technique yielded coffee with the lowest pH, while the French Press and Vietnam Drip methods resulted in brews with similar pH values.This difference might be attributed to the different particle sizes used in these techniques, where the V60 uses a medium-fine grind, which is smaller than that used in French Press and Vietnam Drip.This result is consistent with a previous study that found that the particle size of coffee grounds significantly affected the pH value and acidity of the brewed coffee [16].
Regarding the TDS values, the V60 technique yielded the highest TDS for both brewed Arabica and Liberica coffee, significantly different from the French Press and Vietnam Drip techniques.This higher TDS value may have arisen from the smaller size of the coffee particles used in the V60 brewing technique.Smaller size creates larger surface area in contact with the hot water, thus extracting more compounds from the coffee particles.In addition, the blooming step in which all the coffee ground is covered with hot water might also contribute to the higher TDS in V60.A previous study also found that V60 yielded brewed coffee with higher TDS values compared to French Press and other extraction techniques [18].
As for the lightness (L*) of the brewed coffee, it is evident that the V60 technique produced the lightest brew followed by Vietnam Drip and French Press.This result is likely due to the finer filter used, which more effectively filtered out larger particles that contibute to the dark brown color seen in coffee brews.

Sensory Profiles of Arabica and Liberica Coffee Brew
Following physicochemical analysis, the brewed Arabica and Liberica coffee were evaluated for 23 sensory attributes by eight trained panelists.The sensory profiles for each coffee brew are illustrated in spider charts (Figure 1).Based on the results, it is evident that the effect of different brewing techniques to the sensory profiles of coffee is more pronounced in Arabica compared to Liberica.This might be attributed to the inherently distinct characteristics of Arabica coffee, which is considered to have the most complex flavor compared to others [6].Interestingly, Liberica coffee received higher scores than Arabica in specific sensory attributes, such as aroma (jackfruit, smoky, and spicy), flavor (jackfruit, smoky, roasty, black tea, earthy), taste (bitter), aftertaste (bitter), and body.On the other hand, Arabica received higher scores for attributes like aroma (caramel, chocolate), flavor (dried fruit, chocolate), taste (sweet, sour), and aftertaste (sweet, astringent).
The three manual brewing techniques resulted in coffee brews with distinct profiles.Notably, the V60 technique produced coffee brews with higher intensity in terms of aroma and smoky and roasty flavor, as well as a combination of bitter and sour notes.In addition, the resulting brews displayed bitter aftertaste and fuller body compared to the others, particularly the Vietnam Drip.The French Press technique generally produced brews that resembled those of the V60, whereas the Vietnam Drip IOP Publishing doi:10.1088/1755-1315/1299/1/0120116 produced brews with the least complexity and overall lowest scores for all attributes.It is worth noting that the V60 brewing technique accentuated the unique notes of Liberica coffee, although it tended to introduce a slightly more pronounced bitterness.

Conclusion
In summary, the Arabica and Liberica coffee obtained from Ijen Geopark exhibit distinct physicochemical characteristics.The differences arise from factors including the coffee species and the specific brewing techniques (V60, French Press, and Vietnam Drip) used.The sensory profiles of Arabica and Liberica coffee are distinguishable, with Arabica having sweet and fruity character whereas Liberica having jackfruit, spicy, smoky, and bitter notes.Interestingly, the effect of the brewing techniques was more pronounced in Arabica coffee compared to Liberica.Of particular interest, Liberica coffee, recognized for its resilience to climate change, demonstrates potential for development and may pique interest due to its unique sensory characteristics when brewed using suitable techniques.

Table 1 .
Protocols for Manual Brewing Techniques 2.2.5.Data AnalysisCollected data were tabulated using Microsoft Excel 2013.Descriptive statistics, analysis of variance (ANOVA), and post-hoc analysis at 95% confidence interval were conducted using Minitab 21 Statistical Software (Minitab Inc., State College, Pennsylvania, USA).Sensory evaluation design and data collection were carried out using Redjade Sensory Software (Martinez, CA, USA).Subsequently, the data were analysed using XLSTAT version 2022 (Addinsoft, New York, USA).

Table 2 .
Physicochemical Characteristics of Roasted Arabica and Liberica Coffee . Physicochemical Characteristics of Arabica and Liberica Coffee Brew Notes: Data are presented as means ± standard deviation (n=3).Different notation indicates significant difference between samples (Fisher LSD, α=0.05)