Most connoisseurs agree that in order to extract the proper amount of flavor from black or oolong tea leaves, the water must be as hot as possible. But no matter how much you heat it, water will never get hotter than boiling: 212°F (100°C), minus a degree or two, depending on the altitude and weather.
That’s because water boils (turns to steam) when its molecules acquire just enough energy to overcome the atmosphere’s pressure on the water’s surface and break away into the air. If a molecule happens to acquire more than that amount of energy. it takes its excess energy along with it as it flies out. That extra energy is therefore lost from the water in the kettle and isn’t available to raise its temperature. So your boyfriend scores a point on that one.
But whistling tea kettles can be deceptive. When your kettle emits its first weak peeps, only a few of the more robust bubbles will have succeeded in making it all the way to the surface to release their steam and make the whistle whistle. The water is not yet fully boiling. For your black or oolong tea, then, you have to keep heating until all the water is bubbling furiously, the whistle has been screaming at maximum pitch and volume for at least several seconds, and your kitchen is beginning to fill up with stray dogs.
Green tea, however, follows different rules. Experts say that it should be brewed at a lower temperature of about 165 to 180 °F ( 74 to 82 °C), presumably because higher temperatures could promote oxidation of its valuable polyphenols.
Coffee is an entirely different cup of tea, so to speak. Water that is boiling vigorously isn’t desirable for making coffee because its steam would carry off too many of the volatile, aromatic flavor components, of which coffee has many more than tea. (Nobody has ever said, “Wake up and smell the tea.”) That’s why the crudest and most forthright method of making coffee, boiling the grounds in a pot of water, makes a brew better suited to the inside of an automobile battery than a breakfast cup.
The best ways to make coffee, in my opinion, are the filter method, in which hot water is poured over freshly ground beans in a filterpaper cone and drips through by gravity, and the French press or piston-and-cylinder method, in which hot water is poured over the grounds in the bottom of a tall vessel and allowed to steep for about three minutes, after which a perforated plunger is pushed down to press the “mud” to the bottom.
Whatever the method, water that isn’t hot enough won’t extract enough of the hundreds of chemical constituents that have been identified in coffee, all of which are sensitive to heat, air, and interactions with one another. Which ones and how much of each wind up in your cup depend on such things as the type of coffee, the relative amounts of coffee and water, the particle size of the grind, the mixing action in the brewing apparatus, the temperature of the water, and how long it is left in contact with the grounds. All in all, though, the optimum temperature for coffee water is around 190 to 2oo°F (88 to 93° C), or “just off the boil.”
To settle any domestic dispute, then, I recommend that you get the water to a full, roaring boil, turn off the heat, and quickly pour some onto your tea leaves or bags in a preheated pot. Then count to ten, during which time the water will cool just enough, and hand the kettle to your boyfriend, who may then proceed with his coffee making.
Could Solomon have done better?