Green Tea New and Old: What a Year Does to the Leaf

Green tea declines from the day it is fired, and the decline is uneven across its compounds. Aroma goes first, colour fades next, catechins fall slowly and caffeine barely moves at all. At three months a well-kept tea is close to fresh, at twelve it is noticeably flatter, and at two years it is a different and lesser drink altogether.

The practical consequence is that green tea is the one class where age is almost always a defect. A dark tea or a pu-erh improves with time and a green tea does not, and the absence of a harvest date on most packaging is the largest single information gap in the category.

A drinker who understands the curve can buy better without paying more. The same money spent on this spring’s tea instead of last year’s famous name buys a better cup every time, and the difference is larger than the difference between two grades of the same season.

What changes, and when

The aroma goes first because the volatile compounds are the most fragile part of the leaf. The chestnut or marine note of a good green tea is carried by molecules that oxidise and evaporate at room temperature, and once they have gone nothing in the kitchen restores them. This is why a stale tea can look perfectly acceptable and still disappoint in the cup.

Colour fades next. Chlorophyll degrades under light and under heat, and the leaf turns from bright green to olive and then to a dull brown-green. A yellowed leaf is not automatically a bad tea, but it is a tea that has been sitting, and the colour is the most honest signal on the shelf because it cannot be argued with.

The catechins decline slowly, by perhaps a quarter over a year in a sealed tin kept out of the light. That is slower than most drinkers assume, and it means the health-relevant compounds outlast the flavour by a wide margin. A tea that tastes tired is not necessarily a tea that has lost its antioxidants.

Caffeine is stable for years. A two-year-old green tea has the same caffeine as a fresh one, which matters to anyone counting intake rather than chasing flavour, and it explains why an old tea still keeps people awake at night.

Why the decline is uneven

The four curves move at different speeds because the compounds behind them differ in how readily they react with oxygen. Volatiles are small and reactive and go quickly; chlorophyll is stable until light or heat reaches it; the catechins are protected by the leaf structure and by a dry, sealed environment.

Bitterness follows its own path. The amino acids that give a green tea its sweetness and its savoury depth fall faster than the catechins do, so an old tea tastes flatter and harsher at the same time. The sweetness leaves before the astringency does, which is exactly the wrong order for the drinker.

Moisture is the accelerant for all of it. A tea stored at sixty per cent humidity ages several times faster than the same tea stored dry, and a tin opened and closed daily picks up moisture with every opening. The sealed tin is not fussiness; it is the single largest variable a buyer controls.

What a re-fire hides

A seller holding old stock can re-fire it gently to drive off moisture and restore crispness. The leaf looks better afterwards, the tea crushes rather than bends, and the smell is of toast rather than of paper. Done well, it is a real improvement to a tired tea.

The re-fire does not restore the lost aromatics. It masks them with a toasted note, which is why a re-fired tea smells slightly cooked and then tastes flatter than it smells. The nose is told one thing and the tongue is told another.

That gap between the smell and the taste is the tell, and it is the only reliable one available at home. A tea that smells strongly of toast and tastes of very little has probably been through the process, and a tea that smells of toast and tastes of toast has simply been fired dark in the first place.

The practice is not always dishonest. A producer may re-fire a tea that took up moisture in storage in order to make it drinkable again, and the result is a legitimate tea that is simply not fresh. What is dishonest is presenting it as new, which is common because the customer cannot tell.

• Aroma is lost first and cannot be restored.
• Colour moves from bright green to olive.
• Catechins fall by about a quarter in a year.
• Caffeine is stable for years.
• Amino acids fall faster than catechins, so old tea tastes harsh as well as flat.
• A re-fire masks staleness with a toasted note.
• A gap between smell and taste suggests a re-fire.

How to tell new from old at home

Ask for the picking date before anything else. A seller who can name the week of picking is selling a specific tea; a seller who can name only the year is selling a category. Neither answer is a guarantee, but the difference in specificity tells you which kind of shop you are standing in.

Then look at the leaf. Fresh green tea is a cool, slightly greyish green, and old tea drifts toward yellow and olive. Compare the leaf against white paper rather than against the tin, because the tin is often printed to flatter the contents.

Then smell the dry leaf, and smell it twice. The first impression is the top note, which a re-fire can fake; the second, after the leaf has warmed in the hand, is the base, which it cannot. A tea whose base smells of paper and dust is old whatever its top note says.

Finally brew it and look at the wet leaf. Fresh leaf unfurls into whole, tender shapes with some spring in them; old leaf stays limp and flat, and its liquor is yellow rather than the pale green of a new season tea.

Read the table as a set rather than as individual signs. One yellow leaf proves nothing, but a leaf that is yellow, smells of paper, bends instead of snapping and brews a dull yellow liquor is old tea by any reasonable standard, and no single one of those observations would have been enough on its own.

How to store it properly

An opaque, airtight tin in a cool dark cupboard is the baseline. Light, heat, moisture and odours are the four enemies, and a good tin excludes all four at once. A clear glass jar on a sunny shelf fails on two of them immediately.

Refrigeration helps and it carries a risk. A tin taken in and out of a fridge condenses moisture on the leaf every time it warms, which is worse than plain room temperature. A fridge is worth using only for a large quantity kept sealed and warmed once, not for the tin you open every morning.

Small quantities beat large ones. A hundred grams finished in six weeks is a better purchase than half a kilogram finished in a year, even at a higher price per gram. The saving on the large bag is paid for in the last four months of drinking.

Buy in season. The spring crop arrives in April and May, and a tin bought in autumn is either this year’s stock at its oldest or last year’s at its worst. A shop that sells green tea all year without mentioning the harvest is not tracking it.

None of this is a reason to throw an old tin away. Old green tea still makes a decent cold brew, a perfectly good cooking tea and a fine base for smoking, and using it is better than discarding it.

Frequently asked questions