Effects of grind size, temperature, and brewing ratio on immersion cold brewed and French press hot brewed coffees
2023
Xiuju Wang | Loong-Tak Lim
This study investigated the effects of coffee ground particle size (282–1057 µm volume-weighted mean particle diameter), extraction temperature (4–37 °C), steeping time (5 min to 18 h), and brew ratio (1:3–1:11 ground:water, w/w) on the physicochemical properties of coffee brews prepared using an immersion cold brewing method. The results showed that the extraction rate and yield increased with increasing brewing temperature and decreasing grind size. Brew ratio significantly affected the extraction yield and titratable acidity of the brews, but not the extraction rate. The ratio between the absorbance at 420 nm and total dissolved solid increased with increasing brewing time, suggesting that non-enzymatic browning reactions might have occurred during the extraction process. Strong positive correlations of total dissolved solids with brew physicochemical properties (total phenol content, caffein content, titratable acidity, absorbance at 420 nm) were observed. Compared with hot brew, the cold brew coffees had significantly higher pH (5.18 vs 5.38) and surface tension (61.6 vs 64.5 mN/s) values, but lower titratable acidity (0.97 vs 0.86 g/L), total polyphenol content (4.08 vs 3.40 g/L), and viscosity (1.12 vs 1.08 cSt) values. The findings from this study are expected to be useful for baristas to control extraction efficiency/yield and manipulate brew compositional profiles to impart unique sensory characteristics of cold brew coffee beverages.
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