A hot bath means different things to different people—one man’s “toasty” is someone else’s “scalding.” And so it is with coffee—some may like it hot, but there is a wide range of preferences on just how hot “hot” is.
Fortunately, there is also an objective side to the equation. Coffee and temperature are not just a matter of opinion; science steps in to guide java lovers when heat is having an adverse effect on a cup of coffee.
Brewing Temperature And Effect on Grounds
The best coffee—that is to say, coffee grounds from which the most desirable and the least undesirable chemical compounds have been extracted—requires brewing at as close to 205°—about 45 seconds removed from a full boil—as possible. A water temperature greater than this will burn the coffee, while one less than 195° will fail to extract some of the flavor compounds. Successfully brewing within a range of only ten degrees sounds relatively difficult (and it is), but in fact most decent coffeemakers are designed to do exactly that. When brewing with a French press, a thermometer is crucial.
The Physiology of The Tongue
Assuming your coffee has been brewed at the correct temperature, should you drink it right away? Or does waiting a minute or two create an optimum experience?
As expected, a sliding scale comes into play here, as do different coffee drinkers’ personal preferences. Scientists have long surmised a relationship between taste and temperature, and a 2005 study conducted at the Katholieke Universiteit Leuven in Belgium sought to learn more about microscopic channels in the tongue’s taste buds called TRPM5 that open when taste molecules (sour, sweet, bitter, salty and umami) touch them. Once opened, they then send an electric signal that travels to the brain along nerve fibers, where it is translated into a specific taste sensation. The researchers found that TPRM5 is highly sensitive to adjustments in temperature. Food served at 59º barely caused the channel to open, but when the heat was increased to body temperature (98.6º), TPRM5’s sensitivity was over 100 times higher—and the strength of the electrical signal sent to the brain increased accordingly.
A tongue will burn at approximately one second of exposure to liquid above 160°, and while it’s not been proven exactly how extreme heat effects temperature, it seems reasonable that a burning sensation would mask most, if not all, flavors of a beverage. However, it’s important to note the many psychological benefits of drinking hot beverages, and this is where coffee temperature starts to become a matter of opinion.
Coffee: Temperature Versus Flavor
In 2008, researchers at the National Institute of Health studied the psychological effects of holding a warm cup of coffee in one’s hand. Participants tended to attribute warm feelings to strangers and even found them more trustworthy. Moreover, many coffee drinkers merely want to warm up on a cold winter’s morning, and the hotter the coffee, the better!
On the other hand, when flavor is desired, you’re best off letting your coffee cool—even as low as to room temperature. Coffee cupping or tasting, performed by professionals, involves drinking small amounts of coffee at various temperatures to grade its quality and identify its flavor compounds. The coffee is deliberately cooled while tasting it, knowing that the more subtle flavors present in the brew will not reveal themselves at higher temperatures. At 160°F, the flavor and aftertaste of the coffee can be judged; at 140°F, the cupper can determine acidity and body, and then move on to balance, which is an assessment of how well the flavor, aftertaste, acidity, and body fit together in a synergistic combination. As the brew approaches 100°F, the cupper can, finally, effectively evaluate the sweetness.