Temperature often significantly influences compounds aqueous solubility, so differences in brewing temperatures may result in significantly different compositions in hot brew and cold brew coffees. Brewing coffee is an extraction process dependent on a multitude of variables such as water volume, water temperature, diameter of the coffee grind particles, the porosity of the coffee grind matrix, the pore network between coffee grind particles, and brewing time. Dunkin’ Donuts claims that, “cold brew is less acidic and naturally sweeter than regular coffee, so it can easily be consumed black” 6.Ĭold brew coffee, not to be confused with iced coffee (which is hot brewed coffee served over ice), is prepared at room temperature (20 to 25 ☌ or colder) over a longer time period than traditional hot brewing methods, typically steeping times range from 8 to 24 hours 7, 8, 9, 10. Starbucks markets that cold brew coffee is sweeter, smoother, with a more full-bodied flavor than conventionally brewed coffee 5. In an effort to capitalize on this rapidly growing market, Dunkin’ Donuts, Starbucks, and other commercial coffee vendors have invested in RTD cold brew coffee beverages and are suggesting that colder, slower brewing processes alter flavor, aroma, and bioactive compounds 4. Roast Magazine reports a 460% increase in retail sales of refrigerated cold brew coffee from 2015 to 2017, generating $38 million in 2017 alone 3. Market researcher, StudyLogic, estimates that coffee shop sales of hot coffee fell 3% in 2016, while cold brewed coffee sales were up nearly 80% over the previous year’s record 2. However, cold brew coffee preparation techniques have grown in popularity, both in at-home and consumer (or ready-to-drink, RTD) markets. The majority of coffee consumed in the United States is prepared through various hot brewing methods, whereby the hot water solubilizes and extracts numerous organic compounds from the roasted coffee grounds. In 2015, domestic coffee consumption in the United States reached an estimated 1.4 billion kg/year, making it the second largest coffee market in the world after the European Union 1. 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. 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. 3-CGA concentrations and pH were comparable between cold and hot brews.
Caffeine concentrations in cold brew coarse grind samples were substantially higher than their hot brew counterparts. 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. 3-CGA and caffeine were found at higher concentrations in cold brew coffee made with medium roast coffees, rather than dark roast. 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.
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