The ratio that matters
The ratio that matters for oolong is much heavier than for green or white: one gram to 15 or 20 millilitres. That is 5 to 7 grams in a 100 to 120 millilitre gaiwan.
Oolong is rolled, often into tight balls or long twisted strips, and it is brewed at near-boiling water. The heavy ratio plus short steeps is what produces the layered, aromatic cup the category is known for.
Western brewing works too, at roughly one gram to 50 millilitres, and 3 grams in a 150 millilitre cup is a reasonable starting point. You get a simpler, less aromatic cup, which is a fair trade for the convenience.
The ratio should shift with the roast. A light, floral, ball-rolled oolong wants the full 7 grams in 100 millilitres. A heavily charcoal-roasted one is more forgiving and shows better at 5 grams, where the roast does not overwhelm everything else.
Too little leaf is the most common fault with oolong, because people apply green tea ratios out of habit. The result is a thin cup that none of the aroma survives, and it makes a good oolong taste mediocre.
Too much leaf is hard to achieve in a gaiwan, because the vessel limits how much fits. In a mug it is easy, and it produces a thick, tannic cup that tastes like the worst version of black tea.
Time by the clock
Time by the clock for oolong means short steeps: 20 to 40 seconds for the first infusion, adding 10 to 15 seconds each time after.
This is the category where the clock matters least and the leaf matters most. A ball-rolled oolong needs the first steep just to open up, and it is often worth discarding or treating as a rinse.
Water should be at 95 to 100 degrees. Oolong is partially oxidized and often roasted, and it needs the heat to give up its aromatics. Brewing it at 80 degrees, as you would a green tea, produces a flat cup.
A good oolong gives six to ten infusions, and some give more. The flavour changes across that arc rather than fading, and the middle steeps are usually the best.
Over-steeping a light oolong produces astringency quickly. Over-steeping a roasted one produces a heavy, slightly sour cup. Both are recoverable by shortening the next steep, which is the advantage of brewing in short infusions.
The signal to watch is the aroma on the lid of the gaiwan. When that fades and the liquor goes pale, the leaf is spent. With oolong it is genuinely useful to smell the lid between every steep.
A simple starting recipe
A simple starting recipe: 5 grams of leaf in a 100 millilitre gaiwan at 95 degrees. First steep 30 seconds, then add 15 seconds each time through eight or nine infusions.
Give tightly rolled oolong a five second rinse first. It loosens the leaf and lets the first real steep extract evenly, and it washes off the dust that comes from rolling.
For a Western brew: 3 grams in 250 millilitres at 95 degrees for three minutes, then lift the leaf out. One more infusion is possible but the second is much weaker.
If the cup is thin, add leaf rather than time, and check your water temperature. Both problems present as thinness and both are common.
If it is harsh, shorten the steep to 20 seconds rather than lowering the temperature. Oolong needs the heat, and pulling the time back keeps the aroma while removing the astringency.
One habit worth building: brew oolong in small vessels and drink it over several short steeps rather than one long one. It is how the category was designed to be drunk, and the difference is not subtle.
A gaiwan is the cheapest way to do this and it costs about the same as two packets of tea. It also makes the ratio easy, because a 100 millilitre vessel means 5 grams, and that is the whole calculation.
If you are brewing a roasted oolong, use slightly less leaf and slightly longer steeps. Roast suppresses the aromatics a little, and the extra time brings out the caramelised sweetness without pushing it into harshness.