Why Red tea goes bad
Red tea (what much of the world calls black tea) is fully oxidised, which makes it the most stable of the non-fermented types. The oxidative changes that ruin a green tea have already happened, deliberately, during processing. So red tea rarely rots.
What it does is fade. The brisk, malty or cocoa-ish top note goes first, then the liquor thins, and what is left tastes flat and slightly woody. That is what ‘gone off’ means for red tea in almost every case: not unsafe, just no longer worth drinking.
Which tells you what to build storage around: time and air, not mould. You are slowing a decline, not preventing a hazard.
Moisture is the fastest killer
Red tea is less prone to mould than white or green, but it is not immune, and the failure is easy to miss because the leaf is dark to begin with. Above about 60% relative humidity (especially in a tin opened daily in a steamy kitchen) the leaf can take up enough water to go musty. The signs are a dull, cellar-like smell on the dry leaf and a flat, slightly sour cup.
Coloured bloom means discard it; as with any tea, rinsing will not make mouldy tea safe.
For everyday storage the target is simply a dry cupboard and a genuinely airtight tin. Red tea does not need the fridge, and the condensation you get carrying a cold tin into a warm kitchen is a bigger risk than the staleness you were trying to avoid.
Odor travels
Red tea is a willing odour sponge, and because its own aroma is malty and fairly assertive, a competing smell can hide inside it for a while before you notice it in the cup. Coffee, spices, and anything smoked are the usual culprits.
Keep it sealed and away from the stove and the spice shelf, and do not reuse a caddy that held something else first. Broken grades and CTC, with far more surface area, take on odours faster than whole leaf. One more reason to buy whole leaf if you mean to keep it.
If a batch has picked up a taint, airing can lift a light one. There is no dependable fix for a strong one.
Heat and light cook it slowly
Heat and light damage red tea slowly, which is exactly why they get overlooked. A tin on a sunny counter or above the oven will lose its briskness in a fraction of the time the same tea would last in a dark cupboard. Light fades the leaf and dulls the liquor; heat accelerates the loss of the volatile compounds carrying the aroma.
The fix is unglamorous: a dark, cool, dry cupboard, a tin with a working gasket, and not buying more than you will drink in a year or two.
Red tea does not improve with age, so there is no reason to hold it. The goal is to keep it tasting like it did on the day you bought it.
The habit that prevents all three
The habit that matters most is buying sensibly and keeping the tin closed. Red tea’s decline is mostly repeated exposure to air, so one large tin opened daily fades faster than two small ones where one stays shut.
Portion your stock: a working tin for the week, the rest sealed and dated, both in a dark, cool, dry cupboard, not the fridge and not above the oven. Close the tin immediately after every session; one left open through a long session costs more than a month of decent storage.
Check older stock by smelling the dry leaf before you brew. If it smells flat and dusty rather than malty, it has gone, and no extra leaf or longer steeping will bring the briskness back.
There is one exception worth knowing. A few red teas, particularly some larger-leaf Yunnan batches, hold up past the usual window and round out rather than fade. They are the minority. The safe assumption for anything you buy is that it is at its best within a year or two of packing, and if you are not sure which you have, store it as though it will fade. That is the likelier outcome, and the storage costs you nothing.