Tea is a wonder drink for health, but tea lovers also drink it for the enjoyment and an alertness boost. If you care about the amount of caffeine available to you from the tea, tweak the recommended brewing times.
Chemist Nikolai Kuhnert of Jacobs University Bremen in Germany tells NPR how this works:
When you steep tea, "the caffeine comes out first" from the leaves, says chemist Kuhnert. If you keep infusing, compounds called thearubigins seep out of the plant, and some will actually bind to the caffeine, he says — meaning the caffeine can't then bind to your brain receptors and wake you up. The longer you infuse the tea, the less caffeine that's available to your body, so a shorter brew can also be more invigorating, says Kuhnert.
Conversely, then, if you don't want a caffeine kick, steep for longer. When it comes to caffeine, tea affects us differently than the way coffee does — it's metabolised more slowly, and the compounds in tea can counteract the jitteriness effect of too much caffeine. Still, if you're watching your caffeine intake, watch your brewing time.
NPR's article offers many other tea tips and fun facts, such as the thinner the cup, the longer the brew will stay hot.