Pheophytin
What chlorophyll becomes when heat or acid knocks the magnesium out — and the whole explanation for green tea going olive.
What a drinker notices
- Colour — appearance
Olive, khaki and dull brown-green where the leaf or powder should be vivid. It is a visual fault rather than a taste one, though it usually travels with taste changes because whatever caused it also affected other compounds.
What this gets credited for, wrongly
A khaki matcha is often assumed to be low grade. It may simply be old, or to have been stored warm, or to have been ground with a mill that heated the leaf. Grade and colour correlate, and the correlation is imperfect enough to be worth knowing about.
What it is
Take a chlorophyll molecule and remove the magnesium atom at the centre of its ring, replacing it with hydrogen, and the pigment stops being green and becomes olive-brown. That is pheophytin, the change is one-way, and it is driven by exactly two things: heat and acid. This single reaction explains why an overheated matcha turns from jade to khaki, why a green tea stored warm goes dull, why boiling water dulls a delicate green leaf, and why adding lemon to green tea kills its colour. It is the most useful piece of chemistry a green tea drinker can carry, because every one of those outcomes is avoidable.
Chemically: Chlorophyll with its central magnesium atom displaced by hydrogen.
Where it occurs in the plant
Not present in healthy fresh leaf in quantity. It appears whenever chlorophyll meets heat or acid, so its level in a finished tea records how hard the leaf was fired and how it has been kept.
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.
- Final firing (hiire) — Creates it
- The final firing is a controlled amount of this reaction. A gently fired sencha stays green; a hard-fired one is duller before it ever reaches a cup, and that dullness is not reversible.
- Hojicha roasting — Creates it
- At hojicha temperatures the conversion is total and deliberate. The brown of a hojicha leaf is chlorophyll that has been fully transformed, which is why no amount of careful brewing makes hojicha look green.
- Ageing and storage — Raises it
- Proceeds slowly in storage, faster in warmth and in the presence of moisture. Refrigerating matcha and sealed green tea is aimed squarely at this reaction.
- Sealed yellowing (men huang) — Creates it
- Where chlorophyll goes during the smothering step, it largely goes here. The warm damp hours under cloth are conditions this conversion likes, and the yellow-brown cast of the finished leaf is this pigment standing in for the one that left. It is the same reaction a hard firing runs, arrived at slowly and without much heat.
How brewing brings it out
Extraction rate: Not extracted by water at all
Insoluble like its parent, so it is seen rather than tasted, and only where the leaf is consumed. What temperature affects is not its extraction but its formation: hot water accelerates the conversion in the leaf and in a bowl of matcha as it stands.
Across infusions: Visible in the spent leaf rather than the liquor. A green tea whose brewed leaf is olive rather than green was over-fired or brewed too hot.
Water: Acid drives the reaction hard and fast. A slice of lemon in a green tea dulls its colour within seconds, and the effect is chemistry rather than dilution — the same lemon brightens a black tea, because black tea's colour comes from entirely different pigments.
What you can change
- Keep green tea water below 80 °C
- Do not let matcha stand in hot water before whisking
- Add lemon to black tea, not to green
- Refrigerate matcha and drink it within weeks of opening
Where this gets misdescribed
That green tea browns because it oxidises in storage. Oxidation is part of what happens to an old tea, but the specific colour change from green to olive is this reaction, and it is driven by heat and acid rather than by air.
Teas this compound defines
Read next
- 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.
- Organic acids — The sourness axis, and the reason a tea liquor is mildly acidic — which decides what colour it is as much as what it tastes like.
- Pyrazines — The roasted, nutty and toasted aromas — compounds that do not exist in a tea leaf until heat makes them.
What this page does not say
This record describes a pigment change and what causes it. It makes no statement about what the pigment does in a body.
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.