As with many foods, even tea has a shelf-life, though you might not realise. Its shelf-life compared with many other unpreserved foods is actually quite long, which is why many people are unaware that it can expire. However, as tea is often something consumed over time (like, perhaps, a fine wine), it is preferable to know how to store it in a manner that won’t allow it to prematurely go bad or stale. Most people are first caught out with white or green tea, as oxidation levels are initially low but are a primary factor in deteriorating the tea’s quality.
The first step in storing it properly is to understand a thing or two about the properties of green and white tea in particular. Black and many oolong teas are already heavily oxidised during processing, as a method of attaining very particular and strong flavours. In order for white and green teas to retain their delicate tastes and subtle aromas, they are barely oxidised at all, with white tea being the least oxidised tea available. As one can plainly see, the level of oxidation is clearly correlated with the colour (and thus class) of the tea.
Now what would happen if you started oxidising something such as, say, a green tea, because you stored it improperly? It will actually start to darken and brown, much like in the processing for black and oolong teas. However, since the oxidation is not happening in the same strictly controlled environment as it would if it were actually intentionally being made into a black or an oolong, the degradation of flavour begins.
There are a few things that change the effectiveness of the storage of your tea. Oxygen, light, heat, and moisture are all responsible for degrading the leaves, so the optimal storage area is somewhere that is a) airtight, b) watertight and dry, c) free from heat, and d) in a dark area. Light can cause the pigments and lipids in the tea to oxidise, and the chlorophyll may also decompose. Mildew can be created through exposure to moisture, and heat will cause a number of compounds in the tea to decompose.
Oxygen, however, is one of the biggest offenders, which is why it’s so important that the tea be stored in airtight jars. Large elements of the tea, such as carbohydrates, amino acids and especially polyphenols (such as catechins) are particularly vulnerable to being oxidised by fresh air at this point. Any of the other above problems will only make this oxidation process faster.
The best place for your tea, therefore, is out of direct sunlight – a dark cabinet would be ideal. To be safe, you should make sure this cabinet is well away from moisture (not above a stove top, or outside, etc.) and any place where it might get particularly hot. Summer is a particularly dangerous time for tea, so finding a place in your house that is generally cool is preferable.
It is not advised that you ever refrigerate your tea, as this can cause condensation to form, which will contribute to spoiling it. Generally speaking, you should be able to keep most teas for at least six months before they begin to spoil, if stored correctly. Some rare teas, in much the same manner as a number of different cheeses and wines, can improve with age; however it is suggested that research is conducted into the tea before allowing it to age, as these teas are few in number.
If your tea does become bland in flavour, however, all is not lost – as long as it’s still drinkable, that is. Mint and lemon can be added to give it a flavour boost, and stronger teas can be mixed with the stale tea in order to produce a much more passable concoction.