Coffee cools more quickly

if you wait to add the cream

The temperature of coffee is a hot topic, especially now that vendors may be serving up liability with that cup of latte. So coffee bars, fast food joints, and coffee drinkers might want to remember what two chemical engineering students discovered back in the 1950s: a cup of coffee cools about a minute and a half faster if you wait a little while before adding your milk or creamer.

In 1958, when Cornell University students Darwin Novak and Robert Seidel unveiled their coffee study at the 50th Anniversary meeting of the American Institute of Chemical Engineers in Philadelphia, the rapid cooling of coffee struck many coffee lovers as something of a sacrilege, but because the laws of thermodynamics and the principles of heat transfer can still help answer a “burning” question, Novak, now an engineer with Cabot Performance Materials in Boyertown, Pennsylvania, and a resident of Horsham, has revisited the study for National Engineers Week.

Technology has changed the way many of us brew our coffee, with automatic drip coffee makers and on-the-job instant cup brewers replacing many stove-top percolators. Today’s coffee drinkers also tend to add lower-fat creamers, rather than whole milk or cream; Novak says the trend, if not the exact timing, holds true, and the principles underlying the award-winning project, “The Mechanisms of Cooling Hot Quiescent Liquids,” apply to today’s concerns about coffee’s temperature.

Novak and Seidel based their work on an assumed “pouring point” for coffee of 185 degrees Fahrenheit (5 degrees warmer than the coffee served in some of today’s famous restaurants), and a “safe drinking point” of 143 degrees. In their research, which occupied much of their senior year, Novak and Seidel found that, under laboratory conditions, a cup of coffee took 425 seconds to cool enough to drink if the milk or creamer was put in at once. If you waited 310 seconds to add the milk or creamer, however, the coffee cooled in just 30 additional seconds, or 340 seconds – 85 seconds faster.

Novak says the research, under the guidance of now-retired Professor Ray G. Thorpe, confirmed earlier heat transfer findings on the evaporative cooling of large tanks of coffee and other hot liquids of commercial importance.

“In our everyday lives, most of us tend to take both the lessons of science and the contributions of engineering for granted,” Novak said. He remarked how improvements in technology have changed the kinds of coffee we drink, whether decaffeinated or new specialty blends, as well as the ways in which we produce, store and make our coffee. Novak, who drinks his coffee black, added, “not many of us – even those of us who know better – ever think of that morning cup as being ‘engineered.'”

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