Why Oolong tea goes bad
Oolong is the widest category here and the hardest to give one rule for, because a lightly oxidised, rolled oolong and a heavily charcoal-roasted one barely behave like the same product. Light oolongs (the fresh, floral, greener styles) fail the way green tea does: aroma and freshness go first, and they want cool, sealed storage. Traditional roasted oolongs are far more forgiving. Roasting drives moisture down and stabilises the leaf, so a well-roasted Tieguanyin or a Wuyi yancha keeps for years and often improves as the roast settles.
Knowing which of the two you have is the first step, because the storage that saves one can flatten the other.
Moisture is the fastest killer
Moisture is what undoes oolong. For a light oolong the sequence is familiar: the leaf takes up water, the floral top note goes flat, and the cup turns dull and then slightly sour. For a roasted oolong the risk is different but real: a poorly dried tea can go rancid behind its roast, and the roast that was supposed to protect it masks the problem until it is obvious.
The practical line is about 60% relative humidity or below for drinking stock. If you see bloom, or the tea smells musty rather than roasted, do not try to rescue it by re-roasting at home. That hides the smell, it does not remove it.
Odor travels
Oolong cuts both ways on odour. A strongly roasted or heavily scented oolong will scent everything stored near it, so never keep one in the same cupboard section as a delicate green or white. At the same time the leaf is dry and porous and picks up its surroundings readily.
The rule is to segregate: roasted and scented teas in their own sealed tins, light oolongs with the other delicate teas, nothing aromatic nearby. With roasted oolongs people often mistake a taint for the roast, so compare against a fresh sample before you decide a tea has gone.
Heat and light cook it slowly
Light is the quiet killer for light oolongs, for the same reason it is for green tea: it flattens the aroma and fades the liquor. Roasted oolongs care less about light and more about heat.
A freshly roasted tea carries ‘fire’ (a smoky, drying edge) that normally settles over weeks to months if the tea is left alone, sealed, in a cool place. Store it somewhere warm and the wrong thing happens: the fire bakes in, or the tea stales before it ever rounds out.
Refrigeration is legitimate for light oolongs you will not drink soon, sealed and moisture-proof, brought back to room temperature before opening. Do not refrigerate roasted oolongs. The cold does nothing for them and the condensation risk does real harm.
The habit that prevents all three
Start by sorting what you actually have. Lightly oxidised, greener oolongs go with the teas you plan to drink soon, in a sealed tin in a cool dark cupboard, or the fridge for longer holds. Roasted oolongs go in their own sealed tins at stable room temperature and are left to rest. Many are better six months after roasting than on the day.
Date the tin when you open it, and re-seal immediately after every session. Check lightly roasted stock a couple of times a year by smelling the dry leaf.
If you buy a heavily roasted tea that tastes harsh and smoky, that is often the roast rather than spoilage. Give it a few months sealed before you judge it.
One buying note saves a lot of storage trouble later: ask whether an oolong is roasted, and when. Vacuum-packed light oolongs keep well unopened, but once the pack is broken they behave like any delicate tea and are best finished within a few months. Roasted oolongs bought loose from a shop tin have already had air exposure, so their clock starts when you get them home rather than when they were fired. If you are buying to keep, choose a roasted tea packed soon after firing and leave it sealed until you are ready to drink it. A tin you forget about is, with roasted oolong, usually a tin that improves.