Theaflavins and thearubigins - where the colour and strength of black tea come from
Why does black tea have a coppery-red, deep colour and a full, strong body, while green is pale and delicate? The answer hides in two compounds with difficult names: theaflavins and thearubigins. They form from catechins - the antioxidants of the green leaf - during oxidation, the step that turns green tea into black. Theaflavins give brightness, briskness and a coppery hue, and thearubigins depth, body and a red-brown colour. They are the chemical heart of what sets black tea apart from green. Understanding them is understanding where the colour, strength and character of black come from. Here is a guide to theaflavins and thearubigins: how they form, how they differ and how together they build the flavour of black tea.
From catechins to new compounds
It all begins with catechins - antioxidants present in the fresh, green leaf. When the leaf is subjected to oxidation, its cell structure is disrupted, and an enzyme (polyphenol oxidase) sets off the transformation of the catechins. During it the catechins combine and turn into larger compounds: precisely theaflavins and thearubigins. It is a key moment: the antioxidants of green tea turn into new molecules, which give black tea its colour and flavour. The longer and fuller the oxidation, the more of these compounds form, and the darker and stronger the tea becomes. This is why black tea, fully oxidised, differs so much from green, in which oxidation was stopped. Understanding that theaflavins and thearubigins are products of the transformation of catechins is the starting point for the rest. We cover the step itself more in tea oxidation.
Theaflavins: brightness and briskness
Theaflavins are the first compounds to form during oxidation - they emerge earlier than thearubigins. They are orange to red in colour and give the tea a coppery, lighter hue. In flavour they are responsible for two features: brightness and briskness. Brightness is the impression of freshness and clarity of the brew, and briskness is that lively, slightly astringent, refreshing energy in the mouth, characteristic of a good black tea. It is theaflavins that give tea this invigorating edge and clear shine. They are a prized marker of quality: a tea rich in theaflavins is lively and brisk, not flat. They can be seen as the lighter, more dynamic pole of the two compounds. It is thanks to them that a strong black tea can be refreshing, not just heavy. Theaflavins are the bright, energetic side of black tea.
Thearubigins: colour and body
Thearubigins are the second, later product of oxidation - they form after theaflavins and there are far more of them in black tea. They are red-brown in colour and it is they that are responsible for the deep, dark colour of the black tea brew. In flavour they give three things: colour, strength and body, that is the full, round mouthfeel. It is thearubigins that build the depth, density and substance of the brew, its solid, full structure. They can be seen as the heavier, more massive pole of the two. If theaflavins give shine and briskness, then thearubigins give body and depth. Together they create the full picture, but it is thearubigins that give the tea its characteristic darkness and fullness. This is why heavily oxidised black tea is so dark and full-bodied - thearubigins dominate in it. We cover the regions of black more in black tea.
A table: two compounds
Let us gather the two compounds in one place:
| Trait | Theaflavins | Thearubigins |
|---|---|---|
| When they form | earlier | later |
| Colour | orange-red | red-brown |
| Effect on flavour | brightness, briskness | strength, body |
| Effect on the brew | coppery shine | deep, dark colour |
The table shows the heart of it: theaflavins are brightness and briskness, thearubigins are colour and body. They are two complementary poles that together create the full character of black tea.
The balance of the two compounds
The most important thing in the quality of black tea is the balance between theaflavins and thearubigins. The mere presence of one or the other is not everything - what counts is their proportion. A tea with a good share of theaflavins is bright and brisk, invigorating in the mouth. A tea dominated by thearubigins is dark, strong and full-bodied, but without theaflavins it is often heavy and flat. The best black teas have both in harmony: the shine and briskness of theaflavins plus the depth and body of thearubigins. This is why the proportion of these compounds, shaped by the conditions of processing, decides the final character - colour, flavour and impression. The grower and maker, by steering the oxidation, influence this balance. Understanding that the quality of black is a play of two compounds, and not of darkness alone, is the key to judging tea. Balance is the heart of a good black.
How processing steers the proportion
The proportion of theaflavins and thearubigins is shaped by the conditions of processing, especially the course of oxidation. The time, temperature and humidity during oxidation decide how much of each compound forms. Shorter, controlled oxidation favours keeping more theaflavins, giving a lighter and brisker tea. Longer, fuller oxidation shifts the balance towards thearubigins, giving a darker and heavier tea. Too long an oxidation can even transform the compounds further, towards less desirable forms, which weakens the quality. This is why the maker must steer the oxidation precisely, to hit the desired balance for a given style of tea. This shows that the flavour and colour of black tea are directly designed at the processing stage, by steering this transformation. Oxidation is not just a switch for blackness, but also a precise dial of proportion. We cover the whole process more in how tea is made.
Why it matters for flavour
Understanding these two compounds explains why black teas differ so much from one another. A light, bright, brisk black tea, like many high-mountain Darjeelings, is rich in theaflavins. A dark, strong, full-bodied breakfast tea draws its strength from thearubigins. It is not chance nor the variety alone, but the proportion of these compounds, shaped by oxidation. With this knowledge you can better understand what to expect: a bright, coppery brew announces briskness, a dark, red-brown one announces strength and body. It also explains why a tea strong in colour is not always the best - without theaflavins it is often flat. Balance gives the most. Understanding the chemistry behind the colour of black tea is a higher level of appreciating it, linking what you see with what you sense in the mouth. The colour really does announce the flavour.
How to sense it in the brew
The action of both compounds is easy to observe in the cup. Look at the colour: a coppery, lighter hue betrays more theaflavins, and a deep red-brown more thearubigins. Taste: the lively, slightly astringent, refreshing briskness in the mouth is theaflavins, and the full, dense, round body and depth are thearubigins. A good black tea combines both impressions - it is at once brisk and full-bodied. If a tea is dark but flat and heavy without an invigorating edge, that is a sign of thearubigins dominating without enough theaflavins. Compare a light, bright Darjeeling with a strong breakfast tea, to feel the two poles of these compounds. Over time you will start to read the balance from the colour and the impression in the mouth. It is a skill that deepens the tasting of black tea and links chemistry with flavour.
The essentials in brief
Let us gather it up. Black tea owes its colour and strength to two compounds forming from catechins during oxidation: theaflavins and thearubigins. Theaflavins form earlier, are orange-red in colour and give the tea brightness and briskness - that invigorating, clear edge and coppery hue. Thearubigins form later, there are more of them, they are red-brown and give colour, strength and body - the deep, dark, full-bodied side of the brew. Quality is decided by the balance of both: the shine of theaflavins plus the depth of thearubigins. The proportion is steered by processing, especially the course of oxidation. This is why black teas differ so much, and the dark colour alone does not guarantee quality. Now you know where the coppery-red colour and strength of black tea come from.
Note every tea in GustoNote - including the colour of the brew and the briskness and body you sense. Over time you will start to read the balance of theaflavins and thearubigins, and understand the flavour of black tea more deeply.