Free amino acids
The savoury half of the balance that decides whether a green tea tastes sweet or brisk — and half of the ratio Chinese graders actually use.
What a drinker notices
- Umami — a taste
- Sweetness — a taste
Savouriness and a soft sweetness, felt as tastes on the tongue. A tea rich in this pool reads as mellow and thick-tasting; a tea poor in it reads as thin and sharp even when it is strong.
What this gets credited for, wrongly
This is a POOL, not a compound, and the commonest error is reading 'amino acid content' as a synonym for theanine. Theanine dominates it but the others are not decoration — glutamic and aspartic acid contribute umami directly, and arginine and serine contribute to sweetness and to browning during firing.
What it is
Tea's taste is often described as a contest between two pools: the free amino acids, which taste savoury and sweet, and the polyphenols, which are drying and bitter. Neither number means much alone. What means something is the ratio between them, and it is used directly in Chinese green tea assessment as the phenol-to-amino ratio: a low ratio is a sweet, mellow tea and a high one is brisk and astringent. Everything a grower does to a green tea — shading, picking early, picking young, choosing a cultivar — moves that ratio, and every brewing decision moves which side of it ends up in the cup.
Chemically: The pool of unbound amino acids in the leaf — theanine, glutamic acid, aspartic acid, arginine, serine and others.
Where it occurs in the plant
Highest in young spring leaf and in shaded leaf, lowest in mature summer leaf grown in full sun. Nitrogen fertilisation raises the pool substantially, which is why heavily fertilised Japanese tea is savoury in a way that is agronomic rather than varietal.
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.
- Shading — Raises it
- Shading raises the whole pool, not only theanine, and simultaneously holds the polyphenols down. That is why it moves the ratio so far, so fast.
- Plucking standard — Raises it
- A finer plucking standard — bud and one leaf rather than bud and three — raises the amino acid share, because the pool sits in the youngest tissue while the polyphenols are spread more evenly.
- Roasting — Turns it into something else
- Firing consumes free amino acids into browning reactions with sugars. The savoury taste falls and toasted aroma rises, which is the exchange every roasted tea is built on.
- Hand plucking — Raises it
- Picking each shoot individually is the only method that can choose what to take and what to leave, and this pool is the thing that choice is buying. A hand-plucked lot of bud and one leaf carries a markedly richer pool than a machine-cut lot from the same field on the same day.
- Mechanical harvesting — Lowers it
- A powered blade takes everything at a set height regardless of what is ready, so mature leaf and old stem arrive mixed with the young shoots. The pool is diluted by material that never had much of it, which is the compositional half of why machine-harvested tea is graded lower.
- Stalk picking (jian ti) — Lowers it
- Stalk carries a disproportionate share of this pool, so hand-removing it from a finished oolong takes real sweetness out along with the appearance fault it was removed for. It is done between roasts rather than at the end, which means the maker is choosing the trade twice.
- Refining (shiage) — Leaves it broadly alone
- The refiner changes nothing here and redistributes everything. One intake is separated into leaf, stem, powder and broken fractions whose pools genuinely differ, and the several named teas that come out of it — sencha, karigane, mecha, konacha — are that separation rather than four different harvests.
How brewing brings it out
Extraction rate: Fast — among the first things out of the leaf
Out early and readily at low temperature, ahead of the polyphenols at every temperature and further ahead as the water cools. The ratio in the cup is therefore never the ratio in the leaf, and the brewer decides how far the two diverge.
Across infusions: Depleted quickly. The savoury weight of a shaded tea is largely a first-and-second-infusion property, and a session that goes on long enough will end on the polyphenol side of the ratio whatever it started as.
Water: Soft water flatters this pool; hard water flattens the low-intensity end of a taste before it touches anything else.
Leaf, ratio and agitation: Short contact with a lot of leaf favours the amino acids; long contact with a little leaf favours the polyphenols. Two cups of identical strength can sit on opposite sides of the ratio.
What you can change
- Brew cooler to favour this pool over the polyphenols
- Heavy leaf, short steep
- Stop at the second infusion if savouriness is what you want
- Cold brew, where the divergence is largest
Where this gets misdescribed
That a high amino acid figure is straightforwardly good. It is one half of a ratio, and a tea bred for it and grown for it can taste flat and characterless if the polyphenols have been suppressed too far.
Teas this compound defines
Read next
- L-theanine — The savoury amino acid that makes shaded green tea taste like broth, and the compound that explains why shading exists at all.
- Glutamic acid — The compound umami was defined from, present in tea in free form and responsible for the part of a savoury cup that tastes like stock rather than like tea.
- Arginine — The second most abundant free amino acid in a heavily shaded tea, and the one that reveals how much nitrogen the field was given.
- Catechins — The largest soluble fraction of a green tea leaf, the source of astringency, and the compounds oxidation turns into everything a black tea is.
- Pyrazines — The roasted, nutty and toasted aromas — compounds that do not exist in a tea leaf until heat makes them.
- Strecker aldehydes — Malt. The group made when firing spends the leaf's own amino acids against its own sugars, and the reason the maltiest teas are the ones with the most amino acid to spend.
What this page does not say
This record describes a pool of compounds in the leaf and how much of it reaches the cup. It says nothing about what any amino acid does in a body, and nothing about nutrition.
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.