The gap between a good cup of tea and a bitter one is usually ten degrees of water, or thirty seconds of steeping. People have been drinking tea for thousands of years and most of us still get it wrong: water straight off the boil poured over green leaves, a bag left in long enough to turn the cup to tannin. The leaf is rarely the problem. The water and the clock are.

The tool below handles the part that is just numbers. Pick a tea and it gives you the water temperature, the steeping time, how many times the leaves will keep giving, the caffeine, what it pairs with, and a timer keyed to the steep that chimes when the cup is ready. Toggle between Fahrenheit and Celsius, and, where a tea supports it, between a Western mug and gongfu's short repeated infusions. Start there.

That gets you a correct cup. The rest of this is why the numbers are what they are.

The two things that matter

Temperature and time. Everything else is refinement.

Heat is the bigger lever. Delicate leaves, white and green and yellow, scald in water near boiling: the result is bitter and flat, and no amount of sweetener brings it back. They want water that has come off the boil and rested, somewhere around 175°F. Fully oxidized leaves, black and pu-erh, and every herbal infusion, want the opposite, a hard boil to pull the flavor out at all. Oolong sits in the middle and shifts with the roast.

Time is the lever you keep your hand on. The timer starts at the short end of the recommended range on purpose. Taste it there, then extend. A cup steeped thirty seconds too long cannot be walked back; one pulled early can always go in again.

Why one leaf becomes six teas

White, yellow, green, oolong, black, and pu-erh all come from the same plant, Camellia sinensis. What separates them is oxidation, the slow browning that happens when a picked leaf meets air, the same reaction that darkens a cut apple.

White tea is the leaf barely touched, withered and dried and nothing more. Green tea is heat-fixed within hours of picking, the oxidation stopped before it starts, which is why it stays grassy and bright. Yellow is green tea given an extra sealed, slow yellowing that most producers no longer bother with, which is why you have probably never had it. Oolong is caught in the middle, anywhere from lightly to mostly oxidized, which makes it the widest category of all. Black tea is taken the whole way. Pu-erh is the outlier: not oxidized but fermented, aged for years or decades by live microbes, the only tea that genuinely improves in storage.

Six teas, one bush, one variable turned up by degrees.

Gongfu versus the mug

There are two ways to brew, and the tool will time either.

The Western way is one long steep: a teaspoon of leaf, a full mug, three to five minutes, done. It is simple, and it is most of how tea gets drunk in the world.

Gongfu is the opposite bet. A lot of leaf, a small pot, and a run of very short infusions, the first sometimes only ten seconds. You pour, drink, and pour again, and the tea changes cup to cup as the leaves open. It asks more of you, and it is the right tool for a good oolong or an aged pu-erh, which can give a dozen infusions or more before they are spent. The gongfu mode counts the steeps and adds a little time with each round, the way you would by hand.

Re-steeping, and when a leaf is done

Cheap, broken-leaf tea gives one cup and quits. Whole-leaf tea gives many, and the good ones get more interesting partway through rather than weaker. A quality oolong is often best on its third or fourth infusion; aged pu-erh can run past twenty.

Rolled and compressed teas, ball-rolled oolong and pressed pu-erh cakes, want a quick rinse first: a few seconds of hot water poured over and thrown away, which wakes the leaves and washes off storage. After that, keep going until the cup tastes thin. The leaf will tell you it is finished before any clock does.

Herbal infusions are not tea

Chamomile, rooibos, peppermint, ginger, hibiscus, lavender: none of them contain a tea leaf. They are tisanes, brewed from flowers, leaves, and roots, and the category is older than tea itself. Because there is no Camellia sinensis in the cup, they are all caffeine-free, which is most of the reason people reach for them at night.

They are also forgiving. A full boil and a long steep, five to ten minutes, will not turn them bitter the way it would a green tea, and several hold their heat and flavor long after a true tea would fade. The popular ones are in the tool above, brewed by the same two numbers as everything else.