I have an electric water boiler that will boil water and keep the water at one of three settings (208˚F, 195˚F or 175˚F). When I keep the setting at 208˚F and dispense the water to brew black tea, I have found that the black tea brews weak and flat. Now, at first I found that peculiar since the recommended water temperature for brewing black teas ranges from 205˚F to 212˚F. Furthermore, dispensing the water for brewing green teas makes a very nice tasting green tea brew (recommended temperature for brewing green tea is from 170˚F to 180˚F). So I took a digital thermometer probe and took some actual water temperature measurements. The water temperature inside of the boiler was indeed 208˚F. However, when the water was “dispensed” into a teapot, I took an immediate temperature reading and the water had cooled to 185˚F upon the delivery into the vessel. I can only assume that the complex dispensing hardware of the water boiler causes significant cooling of the water, rendering a much cooler water temperature when the water arrives at the vessel.
When I “reboil” the water in my water boiler and dispense when it is at the boiling point, or boil water on the stove or in the microwave, and pour the sputtering water over my black tea – wonderful results! The water added to the black tea at the boiling point brews the tea at a much stronger and fuller flavor profile. I do believe that the flavor in some of our black teas, such as French Crème Brulee, is intensified with the water at the boiling point.
The difference of a few degrees in tea brewing is critical. The higher the temperature, the more that the tea is “cooked” and more extraction from the tea leaves occur with higher molecular energy. Higher temperature at the boiling point can be a good thing for black teas, but a bad thing for green teas. This is because black teas are more oxidized, and therefore, more stable. Hotter water is needed to bring out the tannins from the black tea into the cup. But, the brewing must be stopped just as the tannins develop to give the tea a nice finish. If the brewing goes too long, a high concentration of tannins can dominate the flavor and bitterness will occur. Green teas are less oxidized and are far less stable. Too high of temperature creates too many acids and an overcooked taste – a bit like when your fresh vegetables get overcooked! Many customers tell me that they use a Keurig or other types of coffee makers to brew their tea. Using this Keurig method, I hear, the black tea turns out great but green tea tastes bad. The reason is that the Keurig generates superhot water, which is great for black tea but not good for green tea!
I have included a recommendation chart here for brewing temperatures and times for different types of teas. If you want to experiment with different strengths of tea, use the basic guidelines for temperature and time – only vary the amount of tea, not the temperature or time! And be careful of water heating gadgets and devices, you might want to use a thermometer to fact check the temperature of the water yourself. Enjoy tea!