The Effect of Time, Roasting Temperature, and Grind Size on Caffeine and Chlorogenic Acid Concentrations in Cold Brew Coffee

Megan Fuller,Niny Z Rao

doi:10.1038/s41598-017-18247-4

Abstract

The extraction kinetics and equilibrium concentrations of caffeine and 3-chlorogenic acid (3-CGA) in cold brew coffee were investigated by brewing four coffee samples (dark roast/medium grind, dark roast/coarse grind, medium roast/medium grind, medium roast/coarse grind) using cold and hot methods. 3-CGA and caffeine were found at higher concentrations in cold brew coffee made with medium roast coffees, rather than dark roast. The grind size did not impact 3-CGA and caffeine concentrations of cold brew samples significantly, indicating that the rate determining step in extraction for these compounds did not depend on surface area. Caffeine concentrations in cold brew coarse grind samples were substantially higher than their hot brew counterparts. 3-CGA concentrations and pH were comparable between cold and hot brews. This work suggests that the difference in acidity of cold brew coffee is likely not due to 3-CGA or caffeine concentrations considering that most acids in coffee are highly soluble and extract quickly. It was determined that caffeine and 3-CGA concentrations reached equilibrium according to first order kinetics between 6 and 7 hours in all cold brew samples instead of 10 to 24 hours outlined in typical cold brew methods.

Highlights

An extensive body of literature exists detailing the chemistry of hot brewed coffee, including quantifying the caffeine concentration as a function of hot water brewing method[11,12,13,14]
Given cold brew coffee’s significant growth in the coffee market and the potential importance of coffee’s bioactive compounds on human health, this research investigated the role of cold brewing methods on the kinetics and equilibrium conditions of two compounds of interest: caffeine and 3-chlorogenic acid (3-CGA)
This work establishes that brewing times near 400 minutes are adequate to extract the majority of available caffeine and 3-CGA in medium and dark roast beans prepared at medium and coarse grinds

Summary

Introduction

An extensive body of literature exists detailing the chemistry of hot brewed coffee, including quantifying the caffeine concentration as a function of hot water brewing method[11,12,13,14]. Roasting Temperature 215 –217 °C 215 –217 °C 223 –225 °C 223 –225 °C acids, caffeine, and other dietary phenolic compounds that include caffeoylquinic acids, dicaffeoylquinic acids, and feruloylquinic acids[15] are abundant in coffee These chlorogenic acid compounds convey bitterness to coffee[11] and are known to be active antioxidants that may cause health benefits in coffee drinkers[16,17,18]. This work studied the extraction kinetics of caffeine and 3-chlorogenic for both cold and hot brew methods using single origin Arabica beans grown in the Kona Region of Hawai’i in order to determine the effect water temperature and brewing time on the extraction kinetics and maximum equilibrium concentration of these two bioactive compounds. Brewing methods employed in this work mimicked standard home-brewing conditions to inform what, if any, differences consumers can expect between hot and cold brew coffees

Methods

Results

Conclusion