Why oolong needs more heat than green
Oolong is partially oxidised, and the leaf is usually rolled into pellets or twisted. Both facts point toward hotter water.
Rolling matters as much as oxidation. A tight pellet will not open below about 90 degrees, and the centre of it never brews at all.
Oxidation matters too. A heavily roasted oolong has already been through considerable heat in processing and wants more of it in the cup.
The result is that oolong is the one category where boiling water is nearly always right, including for the green-leaning styles.
Cooler water is the most common cause of a disappointing oolong, and it is almost never the fault of the leaf.
The contrast with green tea is the useful one. There, hot water ruins the cup. Here, water that is too cool is the failure by a wide margin.
Roast level and oxidation push in the same direction, so no oolong benefits from water cool enough to protect a green tea.
Temperature by oolong style
Green style oolongs, such as a lightly oxidised Ali Shan, sit at 90 to 95. They are the only ones where a full boil is slightly too much.
Medium roast oolongs, including most Tieguanyin, want a full boil. Ninety degrees leaves them thin and slightly closed.
Heavy charcoal roasts want a full boil and a thick walled pot, because they need sustained heat across many steeps.
Aged oolong, roasted every few years, also wants boiling water, and it will take ten steeps or more without falling over.
Bagged oolong and broken grades extract faster and sit at the lower end, around 90.
When in doubt, boil. The number of oolongs ruined by water that is too hot is far smaller than the number ruined by water that is too cool.
A thermometer settles the question cheaply. Most kettles that claim to reach 90 stop short of it, and knowing your own kettle’s real number is worth five minutes.
Gongfu brewing and repeated infusions
Seven grams in 100 millilitres, boiling water, 20 seconds for the first steep, then five seconds more with each round.
Discard the first steep of a ball rolled oolong. It goes into opening the leaf rather than into the cup.
Most rolled oolongs peak between the third and the sixth steep, once the pellet has fully opened.
Keep the water at a boil between steeps. A kettle that switches off and reheats costs you temperature at exactly the wrong moment.
A good oolong will run eight to ten steeps. If yours gives out at four, the water was probably too cool from the start.
Between steeps, keep the kettle hot rather than letting it cool and reboiling. Reboiled water gives a flatter cup across a long session.
Pour with confidence rather than dribbling. A slow pour loses several degrees between the kettle and the pot, which matters more than it sounds.
Water to use and avoid
Moderately mineral water suits oolong best. Around 50 to 150 parts per million gives body without flattening the aroma.
Oolong tolerates hardness better than green or white, because it is brewed strong, but above 200 parts per million it turns dull.
Avoid distilled water. It extracts unevenly and gives a flat cup whatever the leaf is.
Avoid water that has been boiled repeatedly. Fresh water each session makes a noticeable difference across ten steeps.
A carbon filter is enough for most tap water. You do not need anything more elaborate to brew oolong well.
Minerals and temperature are independent variables, so fixing one will not rescue the other.
Practical takeaway
Boil the water. That is the default, and it is right for almost every oolong you will meet.
Use 7 grams per 100 millilitres, which is roughly double what Western habit suggests.
Use short steeps and count them, so you find the ones in the middle that are worth waiting for.
Use porcelain for light oolongs and clay for roasted ones.
If an oolong tastes thin and hollow, raise the water temperature before you do anything else.
When a cup is wrong, change one variable at a time. Temperature first, then dose.
If you take nothing else from this page: boil the water, and use more leaf than feels natural. Those two together fix most bad oolong.