Gallic acid
The gallate group after it has been separated from its catechin — small, sour, drying, and a marker of how far a dark tea has fermented.
What a drinker notices
- Sourness — a taste
- Astringency — a tactile sensation
A thin sourness with a drying edge. In small amounts it reads as liveliness in an aged tea; in larger ones it is the sour note that marks a badly stored or under-rested shou.
How much of it there is matters: Below a modest level it is a positive — a brightness in an otherwise heavy liquor. Above it, the same compound is a fault, and nothing about the compound has changed.
What it is
Gallic acid is what a galloylated catechin leaves behind when the gallate ester is hydrolysed off. In a green tea there is very little of it. In a wet-piled shou pu-erh or an aged sheng there is a great deal more, because the microbial and slow chemical processes at work are steadily stripping gallate groups from the catechins that carried them. That makes it a useful marker of what has happened to a dark tea, and it is directly audible in the cup: it is one of the compounds behind the faint sourness that a young shou or a damp-stored cake can carry.
Chemically: Phenolic acid — the gallate group of a catechin, once it has been cut free.
Where it occurs in the plant
Present in small amounts in fresh leaf and generated during processing wherever galloylated catechins are broken down — pile fermentation, long ageing, and to a small extent hard firing.
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.
- Wet piling (wo dui) — Creates it
- Released in quantity as the pile strips gallate groups from the catechins. The sourness of a freshly piled shou, which resting is meant to settle, belongs substantially to this.
- Ageing and storage — Raises it
- Accumulates slowly in a stored sheng cake as the same hydrolysis proceeds without microbes and without heat.
- Wetting the pile (chao shui) — Creates it
- The water added at the start of a pile is what lets this reaction run at all, and the amount decides how sharp the finished tea will be in its first years. A wetter pile releases more of this and needs a longer rest afterwards, which is the trade a maker is making at the moment the hose is turned off.
- Drying the pressed cake — Raises it
- A pressed cake that dries too slowly through its middle keeps the moisture this hydrolysis needs for far longer than intended. The sharpness a buyer finds in a two-year-old cake is often a drying decision made in its first week rather than anything that happened in storage.
How brewing brings it out
Extraction rate: Fast — among the first things out of the leaf
Small, highly soluble and out fast at any temperature — one of the first things a dark tea gives up, which is why a rinse of a young shou tastes sharpest.
Across infusions: Front-loaded, and largely gone after the first two infusions. A young shou that tastes sour at the start of a session often does not by the middle of it.
Water: An acid, so alkaline water blunts it: the sharpness it contributes is the first thing to disappear in water with high bicarbonate, and its loss is part of why such water makes tea taste flat rather than merely weak.
Leaf, ratio and agitation: Extracts fast and fully. It is at its most noticeable in the first infusion of an aged or fully oxidised tea, where hydrolysis has already released a good deal of it from the gallate esters.
What you can change
- Rinse a young shou and discard, to take the sharpest of it away
- Keep early infusions short
Where this gets misdescribed
That sourness in pu-erh always means storage damage. Some of it is the ordinary chemistry of a young pile settling, and resting the cake genuinely changes it — which is not true of the sourness that comes from actual damp spoilage.
Teas this compound defines
Read next
- ECG (epicatechin gallate) — The other galloylated catechin, and weight for weight the most drying thing in the leaf.
- EGCG (epigallocatechin gallate) — The most abundant catechin in green tea, and the clearest single demonstration that astringency and bitterness are different things.
- Theabrownins — The dark, water-soluble polymers of ripe pu-erh and other dark teas — why a shou is almost black and almost never drying.
- 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.
What this page does not say
This record describes a compound's origin in processing, its taste and its extraction. It makes no statement about what it 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.