Brew-haha?
Coffee Cools More
Quickly
If You Wait to Add the Cream
NEW YORK - 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. But, 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 that 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. "But," 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.'"
Note to Editors: Copies
of the original 80-page report, "The Mechanisms of Cooling Hot Quiescent
Liquids," are available from the AIChE Communications Department, 212/705-7660.
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