The role of roasting in cold brew coffee chemistry is poorly understood. The brewing temperature influences extraction processes and may have varying effects across the roast spectrum. To understand the relationship between brew temperature and roast temperature, hot and cold brew coffees were prepared from Arabica Columbian coffee beans roasted to light, medium, and dark levels. Chemical and physical parameters were measured to investigate the relationships among degree of roast, water temperature, and key characteristics of resulting coffees. Cold brew coffees showed differential extraction marked by decreased acidity, lower concentration of browned compounds, and fewer TDS indicating that cold water brewing extracts some compounds less effectively than hot water brewing. Compounds in coffee did exhibit sensitivity to degree of roast, with darker roasts resulting in decreased concentrations for both hot and cold brew coffees. Total antioxidant capacity (TAC) was only sensitive to degree of roast in cold brew coffees, while hot brew coffees had a constant TAC for all three roast levels. This indicates that the solid bean matrix and its chemical constituents interact with cold water differently than with hot water. Surface wetting, pore dynamics, and solubility all contribute to the extraction potential during brewing and are all functions of water temperature.
Keywords: acidity; antioxidant; coffee; coffee roasting; cold brew.