## 3 Results and Discussion
### Characterization of Cold and Hot Brew Coffee  
#### 3.3.1 Physicochemical Comparison between Cold and Hot Brew Coffee  
The physicochemical characteristics of CBC and hot brew coffee were compared, and the results are shown below (Table 6). The results showed that the TDS of CBC and its hot brew counterpart were comparable. Furthermore, the pH value obtained for both brews was the same. However, the cold brew had a significantly higher TA for all pH endpoints (pH 6.0, 8.0, and 8.2).  
One of the objectives of this study was to optimize CBC close to a hot brew equivalent method, thus accounting for the similar TDS and pH readings. Nevertheless, to achieve a similar TDS from the cold brew technique, a higher C2 WR was needed since a lower water temperature was used for brewing. Consequently, a higher C2 WR would result in much more bioactive compounds being extracted. Although the amount of bioactive compoundscould not be directly measured and reflected by TDS, TA could be measured and showed a higher value than their hot brew counterparts.  
To the authors' knowledge, this is the first study that optimizes, matches, and compares cold brew and hot brew at similar total dissolved solids. Other studies used the same C2 WR for both hot and cold brew methods, which would logically result in significantly different properties. [PERSON] et al. (2019) and [PERSON] (2020) used a 1:10 coffee-to-water ratio and found that TDS and pH were different between CBC and hot brew coffee [22; 24]. The total solid was observed to be lower in cold extraction methods compared with its benchmark hot brew extraction [22]. The differences in water temperature influenced the pH of the final brewed coffee, whereby the pH of the final brew from cold brew was less acidic and ranged from 5.5 to 5.7 compared with the hot brew (French Press) at pH 5.2 [22]. Similarly, [PERSON] (2020) found that acidic compounds were extracted more in hot brew coffee, resulting in a lower pH of 5.0 compared with the pH of 5.2 in CBC [24]. Contrastingly, [PERSON] et al. (2018) reported that the pH of the final brew was not affected by the brewing method [26]. Additionally, [PERSON] et al. (2019) and [PERSON] and [PERSON] (2017) also found that there was little difference in Brix and pH between CBC and hot brew coffee [4; 27].  
Even though similar pH readings were obtained from hot and cold brew coffee, the titratable acidity was higher in the hot brew coffee [16]. Similar results were also reported by other authors [7; 28]. Interestingly, the CBC exhibited a higher TA than hot brew coffee in our study. In a study by [PERSON] and [PERSON] (2018), the coffee variety, grind size, coffee roast profile, and C2 WR remained the same; only the water temperature and brewing time were different [16]. Generally, a higher temperature would result in more extractable soluble acidic compounds, but a longer brewing time used in CBC may compensate for the low water temperature used. However, it should be noted that certain compounds are temperature-dependent, less sensitive to the extraction time, and thus more soluble at a higher temperature [4].  
The TA results in our study can be explained by the difference in C2 WR used. To achieve a similar TDS, a 1:14 coffee-to-water ratio was used for CBC, whereas a 1:18 C2 WR was used for hot brew coffee. The acidic components would be more concentrated in CBC since the water used is less than that used in hot brew coffee.