If you brew every tea you own with boiling water and leave it for five minutes, you are extracting the wrong things from most of them. Green tea brewed boiling tastes like grass clippings; delicate oolongs go flat; even most black teas develop an unpleasant astringency at full boil. Water temperature is the single biggest improvement most home tea drinkers can make.
Temperature by tea type
Green tea: 70–80°C for most styles, lower for delicate Japanese greens like gyokuro (around 60°C). At boiling, the leaves dump bitter compounds quickly and the subtle flavours never come through.
White tea: 75–85°C. Similar to green, slightly more forgiving but still benefits from cooler water.
Oolong: 85–95°C. The range covers a wide style — lighter floral oolongs at the cooler end, darker roasted ones at the hotter end.
Black tea: 95–100°C. This is the one style designed for boiling water. Most supermarket tea bags fall here.
Pu-erh: 95–100°C, often with a quick rinse first to wake the leaves up.
Herbal infusions (chamomile, mint, rooibos): boiling water. They are not technically tea and behave differently.
Hitting the right temperature
You do not need a thermometer. Bring water to a full boil, take it off the heat, and wait. Roughly: thirty seconds drops it to about 95°C, ninety seconds to 85°C, two and a half minutes to 75°C. The exact times depend on your kettle and the room, but they are consistent enough that you will hit close.
If you brew the same tea every day, learn the wait time once and apply it. For a green tea you drink at 75°C from a 1500W kettle in a normal kitchen, the wait is around two and a half minutes. Time the kettle once with a thermometer to calibrate, then never bother again.
Steeping time
Lower temperature usually means slightly longer steeping. Green tea at 75°C for two minutes is a reasonable starting point; black tea at 100°C for three minutes likewise. Adjust shorter if it is bitter, longer if it is weak. Keep notes for teas you like — the leaves vary enough that one bag of green gunpowder is not the same as another.