Physiochemical Characteristics of Hot and Cold Brew Coffee Chemistry: The Effects of Roast Level and Brewing Temperature on Compound Extraction.

Niny Z Rao,Megan Fuller,Meghan D Grim

doi:10.3390/foods9070902

Abstract

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.

Highlights

Coffee chemistry is determined by numerous factors, including the varietal of bean, region of origin, growing conditions, roasting process, grind size distribution, water chemistry, and temperature of water used during extraction
While there exists a significant body of literature on the relationship between coffee bean roasting and hot brew coffee chemistry [1,2,3], there is little understanding of how cold brew coffee chemistry is affected by bean roast
Two previous studies by Vignoli et al showed that degree of roast had little effect on the Total Antioxidant Capacity (TAC) of hot brew coffee [6,28], which agrees with the TAC profile observed in hot brew coffee here

Summary

Introduction

Coffee chemistry is determined by numerous factors, including the varietal of bean, region of origin, growing conditions, roasting process, grind size distribution, water chemistry, and temperature of water used during extraction. Cold brewing has become a popular coffee production method, where coffee is prepared at room temperature (20 to 25 ◦ C or colder) and steeped for 8 to 24 h—much longer than the time required by traditional hot brewing methods. The solid matrix of the coffee bean undergoes important physical and chemical alterations as a function of internal bean temperature. Roasting is achieved by applying hot air to the beans such that a minimum internal bean temperature of 190 ◦ C is sustained for some length of time, usually no less than 3 min [1]

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