Tea Chemistry Explained: Catechins and Theaflavins in Your Cup

Tea chemistry is one of those topics where simple answers do not exist, no matter how badly we want them. A tea leaf is a complex chemical package — catechins, theaflavins, amino acids such as L-theanine, caffeine, and pigments that shape color and taste. No single compound tells the whole story. The interesting part is how the balance shifts: growing conditions, processing, oxidation and aging all change which compounds end up in the leaf, and how much of each reaches your cup.

At Valley of Tea, we have been sourcing and tasting teas for over fifteen years. This guide draws on that experience.

This is where tea enters the conversation, as a drink worth understanding in detail. Tea is a beverage — one that happens to contain a wide range of compounds that researchers have studied extensively. Some of those studies are large. Some are small. All of them deserve to be read honestly, without exaggeration.

This guide covers what is actually in the cup, which teas have been studied most, how to brew them to get the most out of their compounds, and what realistic expectations look like.

What Research Says About Tea Chemistry

The scientific interest in tea chemistry centers on a few key compound groups. Different teas carry different compound groups, which is worth understanding before jumping to any single recommendation.

Catechins in Green Tea

Green tea catechins — particularly epigallocatechin gallate (EGCG) — have been the most studied compounds. The chemistry is straightforward: catechins with gallate esters carry an extra galloyl group, which makes them more reactive and more astringent than their non-gallated counterparts. That galloyl group is also why EGCG accounts for much of the bitterness and astringency in a strongly brewed green tea.

Multiple meta-analyses have looked at green tea catechins. One of the earlier ones appeared in 2011. A larger 2020 meta-analysis (PMC) covered studies that used both brewed green tea and green tea extracts. A 2022 meta-analysis published in Frontiers in Nutrition grouped the studies by length, separating those shorter and longer than 12 weeks.

Most of that research is written for scientists, not tea drinkers. For a tea drinker, the practical takeaway is simpler: EGCG is one of the compounds that gives green tea its brisk, slightly bitter edge.

Theabrownin in Pu-erh

Pu-erh tea has a completely different chemistry. A 2019 study published in Nature Communications identified theabrownin — one of the most abundant pigments in pu-erh tea — as a characteristic compound of the tea. Theabrownin is a large, brown polymer that forms as catechins and theaflavins oxidize and condense during fermentation. It is a major contributor to the dark, reddish-brown color of a ripe pu-erh infusion and to its smooth, mellow body.

This fermentation chemistry is distinct from the catechin chemistry of green tea. It ties pu-erh's character specifically to its post-fermentation chemistry — the microbial processing that creates theabrownin during aging.

Research on pu-erh remains limited compared to green tea. Most of the existing studies come from research groups in Asia, close to where pu-erh is produced. The research is still in earlier stages.

Anthocyanins in Hibiscus

Hibiscus tea (Hibiscus sabdariffa) brings yet another set of compounds — primarily anthocyanins. These are the same pigments responsible for the deep red color of the brew. Anthocyanins shift color with acidity, which is why a squeeze of lemon turns a hibiscus infusion a brighter red.

Published research on hibiscus is mixed in quality and design. One systematic review collected studies on hibiscus infusions. Another review covered 7 studies, and the two reviews were organized quite differently. Many of the studies were small and short, and their designs varied widely.

Teas That Have Been Studied

Green Tea

Green tea is the most extensively researched tea. The main polyphenols are catechins, with EGCG being the most abundant and most studied. A typical cup of green tea contains 50 to 100 milligrams of EGCG, depending on cultivar, growing conditions, and brewing method.

At Valley of Tea, we carry several green teas suited to daily drinking. Gunpowder green tea is one of my personal favourites for everyday drinking: smooth and rich, with a hint of smoke. Gyokuro tends to have the highest catechin concentrations among Japanese greens, and matcha delivers substantially more per serving because you consume the entire ground leaf rather than just an infusion. Genmaicha and Kukicha are also good options if you prefer a lighter, more approachable green tea for daily use.

I brew Sencha at 70 to 80 degrees Celsius and find it holds up well across multiple infusions. For Gyokuro, I drop to 60 degrees to preserve the sweetness and avoid bitterness. If you do not have a thermometer, you can judge by the water: no movement is around 75 degrees, silent steam is roughly 80, a few rising air bubbles is 85, and active bubbling is about 90.

The consistency of the research on green tea chemistry is notable. Across samples from different gardens and harvests, the pattern is always the same: catechins make up the largest share of the polyphenols in the leaf. The amounts vary by cultivar, harvest, and processing, but the pattern holds.

Pu-erh Tea

Pu-erh is a post-fermented tea from Yunnan province in China. The microbial fermentation process creates unique compounds not found in other teas, most notably theabrownin. Research interest in pu-erh chemistry dates back to early studies in the 1980s.

We stock both sheng (raw) and shou (ripe) aged pu-erh. Sheng ages slowly, like fine red wine, and the best comes from old native Yunnan trees — it develops complexity over years of careful storage. Our shou brews a deep red infusion with a hearty sweet aroma, fragrant woods, and what I would describe as mild earthy depths — a forest taste. For storage, pu-erh can be exposed to open air as long as it is not too wet or humid.

Comparative studies have looked at pu-erh, green, oolong and black tea side by side, because all four come from the same plant but differ in processing. Notably, pu-erh is the only one of the four whose character is shaped by microbial fermentation — the others are defined by how far their leaves are oxidized.

Pu-erh's fermented character means much of its original catechin content has been transformed into theabrownin and related pigments. This is a fundamentally different chemistry from green tea's catechin profile. At Valley of Tea, we carry both, and the way they complement each other — a fresh, grassy green next to a dark, earthy pu-erh — is one we find genuinely interesting. Brewing one after the other is the easiest way to taste how differently the same plant can turn out.

Hibiscus Tea

Hibiscus is a caffeine-free tisane (technically not a true tea, since it does not come from Camellia sinensis, but universally referred to as tea). The deep red infusion is rich in anthocyanins, organic acids, and polyphenols.

The research on hibiscus is less consistent than for green tea. Its appeal is easier to describe: a tart, cranberry-like flavor and a vivid red color. For people seeking a caffeine-free option, hibiscus is a reasonable choice, hot or iced.

Rooibos Tea

Rooibos (Aspalathus linearis) is another caffeine-free option that has attracted research attention. It contains unique polyphenols — aspalathin and nothofagin — not found in any other plant.

In South Africa, rooibos is often drunk several cups a day. That is easy to manage, since it is naturally caffeine-free and stays smooth even after a long steep. That smoothness comes partly from its low tannin content compared with black tea.

It is also forgiving to brew. Use water just off the boil and steep for five minutes or longer; it will not turn bitter. Our green rooibos is a good choice for people looking for a caffeine-free option with a smooth, gently sweet taste.

Oolong Tea

Oolong sits between green and black tea in terms of oxidation, and its polyphenol profile reflects this intermediate processing. A large population-based study from southern China (76,979 individuals) recorded daily oolong tea drinking habits across the region. Many participants had been drinking oolong daily for years, a reflection of how established the tea is in southern China.

Oolong also covers a wide range of styles, from lightly oxidized, floral teas to dark, roasted ones.

Oolong's partial oxidation produces a mix of the catechins found in green tea and the larger polymerized polyphenols found in black tea. This is a different profile from both the catechin chemistry of green tea and the fermentation chemistry of pu-erh, adding another dimension to how different teas taste. Our Tie Guan Yin oolong is a good starting point for those new to oolong.

How to Brew for Maximum Compound Extraction

If you are curious about what ends up in your cup, how you brew it matters. Research on brewing parameters and polyphenol extraction provides some practical guidance — and after fifteen years of brewing, I have a few methods of my own.

Green Tea

Studies have found that brewing green tea at 80 to 85 degrees Celsius (176 to 185 degrees Fahrenheit) for 3 to 5 minutes maximizes EGCG extraction while maintaining good flavor. This matches what I do in practice. I use an electric kettle with temperature selection, but I always verify with a thermometer — many kettles are not accurate, and even a 10-degree difference matters for delicate greens.

For Sencha, I aim for 70 to 80 degrees; for Gyokuro, I drop to 60 degrees to preserve the sweetness and avoid bitterness. If you do not have a thermometer, you can judge by the water: no movement is around 75 degrees, silent steam is roughly 80, a few rising air bubbles is 85, and active bubbling is about 90. I always preheat the teapot first.

Using loose-leaf tea rather than bags generally provides better extraction because the leaves have more room to expand and release compounds. However, research has also shown that tea bags can produce higher polyphenol concentrations per cup due to the finer cut of the leaf, which increases surface area.

Pu-erh Tea

Pu-erh is traditionally brewed with fully boiling water (100 degrees Celsius / 212 degrees Fahrenheit). The compressed, aged leaves require higher temperatures to open up and release their compounds, including theabrownin. A brief rinse of 5 to 10 seconds with boiling water before the first steep is standard practice — it washes the leaves and begins to hydrate them.

Pu-erh is well-suited to multiple short infusions (gongfu style), with each steep extracting different compounds. The first few steeps tend to be richest in water-soluble compounds.

Hibiscus and Rooibos

Both hibiscus and rooibos benefit from near-boiling water and longer steep times. Research on polyphenol extraction from herbal teas indicates that temperatures between 90 and 100 degrees Celsius with steep times of 5 to 10 minutes optimize polyphenol release. For hibiscus, the anthocyanins responsible for its color extract readily at these temperatures.

Cold Brewing

Cold brewing green tea at room temperature (approximately 20 degrees Celsius) for 12 hours produces an infusion with a high polyphenol content, with higher yields of certain catechins (epicatechin and epigallocatechin) compared to hot brewing. This only works well with whole loose leaves, not powdered tea.

A Practical Note

Adding lemon or citrus to green tea has been shown to increase total polyphenol content of the beverage, likely by stabilizing catechins in the acidic environment. Milk, on the other hand, binds to catechins in green tea and mutes their astringency — which is also why milk softens a strong black tea.

Realistic Expectations: Tea Is Not Medicine

This is the section that matters most, and the one most tea content glosses over.

Many studies of green tea catechins use concentrated extracts rather than brewed tea. A cup of brewed tea is something else entirely: a drink made for flavor. Tea is a beverage, not a medicine. Anyone with a health concern should talk to a healthcare provider, not a tea merchant.

What the research does suggest is that green tea, pu-erh, oolong and rooibos each have a distinct chemical profile, best enjoyed as part of an overall varied dietary pattern. The operative words are "distinct" and "as part of."

The studies also show that the amount of each compound in the cup depends on how much leaf you use and how long you steep it. One cup now and then is a fine way to get to know a tea. In cultures with long traditions of daily tea drinking, several cups a day is simply normal. There, tea is simply part of the day.

Most large-scale studies on tea drinking are surveys of habits, so they describe who drinks tea rather than what tea does. People who drink tea regularly also tend to share other habits and routines. Controlled studies on tea tend to be smaller and shorter in duration.

A Balanced Approach

The most honest thing a tea company can tell you is this: tea is a good daily habit, worth drinking for its flavor, and the research on it is real but limited. It is not a treatment for any medical condition.

In our experience, people who come to tea out of curiosity about its chemistry are just as consistent in their habits as those who come for the taste. That consistency is what matters — it is daily drinking over months, not occasional cups, that turns a tea into one you know well. Whether your reason for starting is curiosity about the chemistry or simply enjoying a well-brewed Gyokuro, the routine is the thing.

Tea fits naturally into an everyday pattern of living, alongside good food and good company.

If you are interested in exploring teas whose compounds have been studied in depth, green tea and pu-erh have the most research behind them. Oolong, rooibos, and hibiscus each have a smaller body of research that is still growing. All of them are worth drinking simply because they taste good and have been enjoyed by people around the world for centuries.

Start with what you enjoy. Brew it well. Drink it regularly. And for any health question, talk to your doctor.

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