Role of roast on chemical characteristics of cold brew coffee

Hot and cold brew coffee samples brewed using Columbian coffee beans roasted at five different roast temperatures (174°C, 183°C, 194°C, 203°C, and 209°C) were analyzed. Caffeine concentration, total caffeoylquinic acid (CQA) concentration, total antioxidant activity, pH, total titratable acids, and total dissolved solids (TDS) were evaluated. Caffeine concentration ranged from 943.21 mg/L to 1055.60 mg/L and from 417.67 mg/L to 1147.59 mg/L for hot and cold samples respectively. Total CQA concentration ranged from 291.30 mg/L to 3213.21 mg/L and from 311.95 mg/L to 1648.47 mg/L for hot and cold samples respectively. In general, the hot brew method yielded higher caffeine and total CQA concentration than the cold brew method. Hot brew coffee samples exhibited a higher antioxidant capacity over cold brew coffee samples using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) decolorization assay. Coffee pH increased as roast temperature increased. At the same roast level, the pH between hot brew and cold brew coffee samples were comparable. The hot brew coffee samples were also found to have higher concentration of total titratable acids. Total dissolved solids (TDS) was observed to be greater in hot brew coffee samples than in cold brew counterparts. Increases in roasting temperature also led to an increase in TDS across coffee samples for both hot and cold brewing methods, with the highest TDS present in hot brew coffee samples roasted at 209°C. It is noted that with the exception of pH, all attributes of hot brew coffee samples have a direct relationship with roasting temperature, while increasing roast temperature exhibited an inverted u-shaped trend in the cold brew coffee samples. The results suggest that the bean roasting temperature significant impacts the chemistry of the final coffee brew and should not be ignored when crafting cold brew coffee beverages.