Recently, both small and large commercial coffee brewers have begun offering cold-brew coffee drinks to customers with the claims that these cold-water extracts contain fewer bitter acids due to brewing conditions (Toddy website, 2016) while still retaining the flavor profile. Dunkin Donuts’ website suggests that the cold-water and long brewing times allow the coffee to reach “... its purest form.” With very little research existent on the chemistry of cold-brew coffee consumers are left to the marketing strategies of Starbucks and other companies regarding the contents of cold-brew coffee. This research analyzes the caffeine and chlorogenic acid (3-CGA) content of cold-brew coffee as a function of brewing time, grind size, and roasting temperature of coffee beans sourced from the Kona region of Hawaii using high pressure liquid chromatography (HPLC). Coarse, medium, and espresso grinds of both dark and medium roasts were analyzed by mixing 350mL of filtered water with 35g of coffee grinds under constant stirring at 20°C. Sampling was performed every 15 minutes for the first hour, then every 30 minutes for the next ten to twelve hours, with a final sample being drawn at 24hours. Equilibrium concentrations for both 3-CGA and Caffeine were reached following 600 minutes, except in the case of the espresso grind size, due to sampling limitations and possibly slow diffusion times through the sample matrix. The caffeine concentrations ranged from 935mg/L to 1475mg/L. Variation was seen as a function of roasting temperature, and less so grind size. The 3-CGA concentrations were found to range from 345mg/L to 547mg/L. In both cases, the medium grind dark roast coffee produced the highest concentrations of caffeine and 3-CGA while coarse grind dark roast produced the lowest concentrations of caffeine and 3-CGA.

Investigation of the kinetics and equilibrium chemistry of cold-brew coffee: Caffeine and chlorogenic acid concentrations as a function of roasting temperature and grind size

253rd National Meeting (2017)

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