Microwaves are wonderful – the fact that you can make good hot food within two minutes… who wouldn’t want that deal? From pizza bagels, to beef stroganoff, to mini desserts – it is something utilized again and again. One thing it shouldn’t be used for though, is to boil water for your tea. It’s better to put the kettle on instead of the microwave.
As Nadia Amugram answers in her Newsminer Article, it makes a lower quality type of boiled water and a lower quality type of tea inevitably. Your standard every day cup of black tea needs to be steeped in water that has come to a rolling boil. A kettle is designed to heat water evenly to 212 degrees Fahrenheit. When you put that kettle on the burner, it creates a natural convection current: The hot water rises and the cool water falls in a cyclical fashion, which uniformly heats the contents of the kettle to a boil. This should be the same concept with electric kettles as well.
Microwaves don’t heat water evenly in the way that a kettle would. Microwaves shoot tiny waves into the liquid at random locations, which causes the water molecules at those points to vibrate rapidly. If the water isn’t heated long enough, the result is isolated pockets of very hot or boiling water amid a larger body of water that’s cooler. Such water may misleadingly exhibit signs of boiling despite not being a uniform 212 degrees. For instance, what appears to be steam rising from a mug of microwaved water might only be moist vapor evaporating off the water’s surface and condensing into mist on contact with cooler air. The same thing happens when you can see your breath on a cold day. A microwave can also overheat the water. The longer water boils, the more dissolved oxygen it losesand many tea experts say that dissolved oxygen is crucial for a bright and refreshing brew. Microwaved water can also be taken to several degrees above boiling if heated for too long This destroys desired aromatic compounds and makes a less tasty tea by over cooking the leaves. Overheated water can even accentuate the naturally occurring impurities in the water that could bring a cup from good to “iffy”.
Microwave heated water just isn’t the same and won’t make the tea in that correct way. As Amugram writes,
” When tea leaves meet hot water, hundreds of different compounds that contribute flavor and aroma dissolve and become suspended in the water. Black tea contains two kinds of complex phenolic molecules, also known as tannins: orange-colored theaflavins and red-brown thearubigins. These are responsible for the color and the astringent, brisk taste of brewed black tea, and they are extracted only at near-boiling temperatures.Water also cooks certain volatile compounds, chemically altering them to produce more nuanced flavors and aromas, such as the earthy, malty, and tobacco notes in black tea. When the water isn’t hot enough to instigate these reactions and produce these bold flavors, tea tastes insipid”
To make a good solid tea, you should put the kettle on instead of the microwave. It just tastes better and makes the tea that much better. Not all tea should be brewed at a rolling boil though – herbal teas and green teas need a not quite boiling cup of water so they do not become bitter. So if you’re making water for teas like that, you should let the water sit a bit before brewing.