My tea is past the date on the packet

In short

The date on a tea packet is a quality date rather than a safety one, and it was set for a sealed packet in a warehouse rather than for yours. What actually matters is which category it is, whether it has been opened, and how it has been kept since — and for one whole category the date is meaningless in the opposite direction, because the tea is meant to keep changing.

Likely causes, in order

Most likely first. Answer the question under each one before moving on — several of these look alike in the cup and are told apart only by what was done to the leaf.

1. 1. The clock that matters started when you opened it, not when it was packed

   Storage

   Check: Has the packet been opened, and roughly how long ago? Is it resealed properly or folded over?

   Fix: An unopened foil packet and an opened one age at completely different rates, and only one of those was in the packer's mind when the date was printed. Judge an opened packet by its own age since opening. Squeeze the air out before resealing; the headspace is doing more harm than the calendar.

2. 2. Green tea and matcha have the shortest honest window of any category

   Leaf quality

   Check: Is it green tea or matcha, and does the dry leaf still smell of anything when you open it?

   Fix: These fade fastest and fade first in aroma and sweetness while astringency remains, so the result is thin and harsh at once. Smell the dry leaf: if it smells of almost nothing, no brewing adjustment will bring it back. Matcha additionally goes dull green or khaki, which is visible.

3. 3. Roasted and fully oxidised teas outlast their dates comfortably

   Leaf quality

   Check: Is it a black tea, a roasted oolong or a hojicha, and has it been dry, dark and sealed?

   Fix: These are the durable categories. A year past the date on a well-kept black tea is usually a non-event, and a roasted oolong that has gone dull can often be brought back by a short low re-firing, which is a standard trade practice rather than a trick.

4. 4. For dark tea the date is measuring the wrong thing entirely

   Leaf quality

   Check: Is it pu-erh, Liu Bao or another compressed dark tea, and does it carry a production year as well as or instead of a best-before date?

   Fix: This category is sold by production year because age is a feature. A best-before date on a pu-erh cake is a regulatory formality. Ignore it and judge the tea, which is the same thing the market does.

5. 5. The date was never a safety statement

   Storage

   Check: Does the leaf look, smell and feel normal — dry, loose, no clumping, no musty or sour note?

   Fix: Dry tea kept dry does not spoil in the way a food does; it fades. What would make it unfit is moisture, and moisture announces itself as clumping, a damp feel and a musty smell. Those signals, not the printed date, are the ones to act on.

Related problems

Sharing a cause category, a tea type or a brewing method with this one.

• I bought a big bag to save money and it was stale before I finished it — A large quantity bought at a good unit price faded well before it was drunk, so the saving turned into waste.
• I think the famous tea I bought is not what it claims to be — A tea sold under a protected or famous place name — West Lake Longjing, Tongmu Zheng Shan Xiao Zhong, a named pu-erh village, Anxi Tie Guan Yin — does not match its descriptions, and the price was suspiciously reasonable.
• My matcha powder has gone dull green or khaki — The powder that was vivid green when the tin was opened is now olive, khaki or faintly brown, and the bowl looks muddy rather than bright.
• My pu-erh tastes exactly the same as when I bought it — A cake bought several years ago to age has not noticeably changed, and it was stored carefully.
• My tea goes damp within weeks and I live somewhere humid — Leaf that arrived loose and crisp becomes soft, slightly clumped and quiet within a few weeks, and the aroma flattens long before any best-before date is close.

Sources