Leaf lipids
The fraction a drinker never tastes and cannot do without: the raw material every green-leaf aroma is cut from, and the part of the leaf that goes off.
What a drinker notices
- Nothing a drinker can detect — not perceptible
Nothing. These are not water-soluble in any quantity that matters and a drinker never meets them; what reaches the nose is always a fragment of one, made by an enzyme in the factory or by oxygen in the packet. A record that gave them a taste would be inventing one, and the entity has a value for exactly this case.
What this gets credited for, wrongly
Staling in green tea is blamed on light, on air and on time as though they were three separate agents. They are three ways of describing one reaction on one fraction, which is why a cold, dark, airless, small package works and any of those measures on its own only half works.
What it is
Nothing in this record reaches the cup, and it is still one of the more consequential entries in the catalogue. The tea leaf's cell membranes are built from unsaturated fatty acids, and two separate things happen to them. When the leaf is damaged — plucked, carried, bruised, rolled — its own enzymes cut those fatty acids into the six-carbon aldehydes and alcohols that smell of cut grass, within seconds. That is where green-leaf character comes from, and until this record existed the model had the products and not the source. Then, over months in a bag, the same fatty acids react slowly with oxygen without any enzyme at all, and the fragments that come off that reaction smell of old oil and cardboard. Fresh green tea and stale green tea are the same chemistry running at two different speeds, and knowing that turns storage advice from a list of rules into a single idea: the fraction that gives a green tea its smell is also the fraction that spoils.
Chemically: Membrane glycolipids and phospholipids and their unsaturated fatty acids, chiefly the eighteen-carbon ones.
Where it occurs in the plant
Everywhere there is a living membrane, so highest in young actively growing tissue and in the chloroplast membranes of the leaf. Shaded leaf runs a larger photosynthetic apparatus to compensate for the lower light, and the character of matcha and gyokuro owes something to the fraction that goes with it.
What processing does to it
In tea, processing is not a modifier applied to a fixed composition — it is what decides the composition. These are the steps that move this compound, and each links to the step itself.
- Hand plucking — Turns it into something else
- The reaction starts at the break. A cleanly picked shoot placed gently in a basket has begun making green-leaf aroma from this fraction before it has left the field, and a crushed one has made a great deal more of it.
- Mechanical harvesting — Turns it into something else
- A powered blade damages far more tissue than a hand does and does it to leaf of every age at once. The grassy edge of mechanically harvested material is this fraction being cut up at the moment of harvest rather than anything that happens later in the factory.
- Bruising (shaking) — Turns it into something else
- Deliberate damage in oolong manufacture, applied at the leaf edge and repeated. Each shake cuts more of this fraction into aroma, and the maker is metering the reaction rather than starting it.
- Rolling and shaping — Turns it into something else
- The most thorough cell rupture in ordinary tea manufacture, and it takes this fraction with everything else. It is why rolled leaf smells sharply green immediately afterwards and why the smell of a rolling room is unmistakable. Pounding to a paste destroys more structure still and smells of almost nothing, because the leaf is steamed first and the enzymes are already dead.
- Repeat rolling and roll-breaking (fu rou) — Turns it into something else
- Rolling in two or three passes with the lumps broken up between them reaches tissue a single long pass never gets to, because one pass tightens the outside of a ball of leaf and stops. Each additional pass opens fresh membrane, so the conversion is metered across the sequence rather than delivered at once.
- Fresh-leaf transport and holding — Turns it into something else
- The reaction does not wait for the factory. A packed bag of fresh leaf warms itself on the road, and enzymes are cutting this fraction into aroma for every one of those hours — before anybody has decided what the leaf should become. It is the reason transport time is a manufacturing variable rather than logistics.
- Kill-green (fixation) — Locks it in place
- Heat denatures the enzymes that do the cutting, which stops new green-leaf aroma being made and locks in whatever has been made so far. Green tea is defined by where in this sequence the heat arrives.
- Withering — Lowers it
- A long wither works through part of this fraction slowly and without much damage, which gives a different product mix from the violent conversion of rolling. It is one reason a withered leaf smells sweet and a rolled one smells sharp.
- Final firing (hiire) — Lowers it
- The finishing fire drives off the more reactive light material and lowers the moisture that the slow oxygen reaction needs. This is why a well-fired sencha keeps longer than a lightly fired one and why refiners regard hiire as a shelf-life decision as much as a flavour one.
- Holding maocha before pressing — Lowers it
- Unfinished tea held before refining is still losing this fraction to slow oxidation, quietly and without an enzyme. It is the reason maocha storage is a period with a cost rather than a neutral pause.
- Pounding to a paste (mortar-beaten leaf) — Leaves it broadly alone
- Rupture without enzyme. The leaf is steamed before it reaches the mortar, so the lipoxygenase pathway that turns membrane lipids into green-leaf volatiles during rolling is already dead — the cells are destroyed more completely than rolling destroys them and almost nothing aromatic follows. It is the cleanest illustration in the catalogue that maceration only smells green when something is alive to act on it.
How brewing brings it out
Extraction rate: Not extracted by water at all
Effectively insoluble in water at any brewing temperature. Whatever a hot infusion does to the leaf, this fraction stays in it — which is a genuine and slightly surprising fact about drinking a plant that is nearly a tenth lipid by dry mass.
Across infusions: Never arrives, at any infusion. What changes across a session is the supply of fragments already made, not the fraction they came from.
Water: Irrelevant to brewing and decisive in storage. Oxygen and warmth are what act on it, so the useful variable is the packet rather than the kettle.
Leaf, ratio and agitation: The state of this fraction is what a drinker is judging when they smell a bag of green tea before buying it. A flat, faintly waxy smell where there should be a sharp green one is the slow reaction having already run.
What you can change
- Buy green tea in small quantities and drink it while it is young
- Keep it cold, sealed and away from air rather than only away from light
- Reseal after every use; headspace is the variable most people ignore
- Smell the dry leaf before brewing — this is the fraction that tells you the tea's age
Where this gets misdescribed
That green tea goes stale because its aroma compounds evaporate. Some of that happens, and the larger change is a reaction rather than a departure: the fraction those compounds were cut from keeps reacting with oxygen and produces different, unwanted ones. That is why a sealed tin of old green tea smells wrong rather than smelling of nothing.
Teas this compound defines
Read next
- Green-leaf volatiles — The smell of cut grass, made within seconds of the leaf being damaged, and the aroma most of tea processing exists to get rid of.
- cis-3-Hexenol — Leaf alcohol: the specific compound behind the smell of freshly cut grass, and the one a tea maker is judging when they smell a withering trough.
- Chlorophyll — The green of the leaf, and — because it barely dissolves — the reason a steeped green tea is yellow while a whisked one is green.
- Carotenoids — The yellow-orange pigments hidden under the green — and the raw material for a good part of tea's fruit and floral aroma.
What this page does not say
This record describes a fraction of the leaf, what processing does to it and why it matters for storage. It says nothing about the fat content of a cup of tea or about anything this fraction does in a body — and since it does not dissolve, the question a nutrition label would ask does not arise here.
Sources
- TeaHQ editorial synthesis — TeaHQ
This page is TeaHQ’s own synthesis of well-established tea chemistry. No external technical document stands behind it, and that constraint is why there are almost no numbers here: directions, rankings and mechanisms are stated plainly, quantities are not, because a figure nobody can check would look more authoritative than it deserves.