What Are the Catechins in Green Tea and Why Do They Matter

If you've ever wondered what makes green tea taste the way it does — why it's grassy and astringent and slightly bitter, why it changes character depending on how you brew it, why some people claim it has health benefits and others are skeptical — the answer is mostly catechins.

Catechins are the polyphenols (a class of plant compounds) that make up 25–35% of the dry weight of green tea leaves. They're responsible for most of green tea's flavor characteristics, most of its antioxidant activity, and almost all of the brewing science that determines whether your cup tastes good or bad.

This post is the chemistry. What catechins are, what they do in the cup, what the health research actually says, and why the brewing temperature matters more than you think.

What catechins are

Catechins are a subgroup of flavonoids, which are a class of polyphenols found in many plants. They're characterized by a specific chemical structure — multiple phenol rings with hydroxyl groups — that makes them effective at binding to metals and neutralizing free radicals. That antioxidant activity is what most of the health claims about green tea are based on.

The main catechins in green tea:

• Epigallocatechin gallate (EGCG). The most abundant catechin in green tea, accounting for about 50–60% of total catechin content. Also the most studied for health effects.
• Epicatechin gallate (ECG). About 10–15% of total catechins.
• Epigallocatechin (EGC). About 10–15% of total catechins.
• Epicatechin (EC). About 5–10% of total catechins.

There are smaller amounts of other catechins (catechin, gallocatechin) but the four above make up the bulk.

The "gallate" versions (EGCG and ECG) are the most biologically active. They're also the most astringent in flavor — that dry, mouth-coating sensation you feel on your tongue after a sip of strong green tea is the gallate catechins binding with proteins in your saliva.

Where they come from

Catechins are produced by the tea plant (Camellia sinensis) as defensive compounds. They're part of the plant's immune system — they deter insects, slow fungal growth, and respond to environmental stress. The catechin content of a leaf varies based on:

• Plant variety. Assamica varieties (used for most Indian and Sri Lankan tea) have lower catechin content than sinensis varieties (used for Chinese and Japanese tea). Green tea from sinensis varieties has more catechins than black tea from the same varieties.
• Growing conditions. Tea plants grown in full sun produce more catechins than shade-grown plants. The shade-grown teas (gyokuro, matcha) have less catechin content but more chlorophyll and amino acids (L-theanine), which is why they taste sweeter and less astringent.
• Leaf age and position. Younger leaves (the top two leaves and bud, which become sencha and gyokuro) have higher catechin content than older leaves.
• Harvest season. First flush teas have slightly different catechin profiles than later flushes — more of the gallate forms.

The total catechin content of a typical sencha is about 12–18% of dry leaf weight. That sounds like a lot, but most of it stays in the leaf. The brewed cup contains a much smaller percentage of the total catechins — typically 200–400 mg per 8 oz cup, depending on brewing.

What they do in the cup

Catechins are water-soluble, which is why they extract into brewed tea. They extract at a temperature-dependent rate: faster and more completely at higher temperatures, slower and less completely at lower temperatures.

This is where brewing matters. The catechins in green tea are what produce:

• Astringency. The dry, puckering sensation on the tongue and cheeks. This is the catechins binding with salivary proteins and precipitating them out. It's the same chemistry as red wine astringency (tannins) or unripe banana astringency.
• Bitterness. A subset of catechins (especially EGCG) taste bitter on the back of the tongue. The bitter taste is distinct from the astringent taste, even though they often appear together.
• Color. Catechins oxidize during processing to form theaflavins and thearubigins, which are the pigments that make black tea dark and brown. Green tea skips this oxidation step (the leaves are fixed by steaming or pan-firing within hours of harvest), so the catechins stay in their original form and the brewed tea stays pale yellow-green.

The balance of sweetness, bitterness, and astringency in a brewed cup of green tea is heavily determined by how the catechins extracted. Brew at 160°F for 60 seconds and you get a sweet, vegetal cup with mild astringency. Brew at 212°F for 3 minutes and you get a bitter, harsh, very astringent cup.

Why temperature matters

The catechins degrade at high temperatures. Specifically:

• Above 175°F: Catechins begin to break down and oxidize rapidly, producing bitter compounds and losing antioxidant activity.
• 160–170°F: Catechins extract steadily without significant degradation. This is the target window for sencha, gyokuro, and most green teas.
• Below 150°F: Catechins extract slowly, but amino acids (L-theanine) and sugars extract at a similar rate. The cup is sweeter, less astringent, more delicate.

This is why green tea brewing temperatures matter so much. The chemistry doesn't lie. Brewing sencha at boiling doesn't make it "stronger" — it makes it bitter and degraded. Brewing sencha at 160°F extracts the same catechins but preserves the compounds that give the cup its characteristic balance.

For our full sencha brewing method, see our how to brew a proper cup of sencha post.

What the health research actually says

Green tea (and catechins specifically) have been studied extensively for health effects. The honest summary:

What the evidence supports:

• Antioxidant activity. The catechins in green tea are effective free-radical scavengers in vitro. Whether this translates to measurable health benefits in humans is debated, but the chemistry is real.
• Modest metabolic effects. Some studies show small increases in fat oxidation and metabolic rate after green tea consumption. The effects are real but small — not a substitute for diet and exercise.
• Cardiovascular markers. Regular green tea consumption is associated with modest improvements in LDL cholesterol and blood pressure in observational studies. The effect size is small but consistent across studies.

What the evidence doesn't support (or supports weakly):

• Cancer prevention. Despite decades of research, the evidence that green tea prevents cancer in humans is weak and inconsistent. Some population studies show small protective effects, others show none.
• Weight loss. Green tea extract is a common ingredient in weight loss supplements. The actual weight loss effect is minimal — measurable in metabolic chambers but not in real-world conditions.
• "Detoxification." Green tea doesn't "detox" anything in any medically meaningful sense. The liver and kidneys handle detoxification; green tea is just a beverage.

The honest framing: green tea is a low-calorie, antioxidant-rich beverage that's a reasonable part of a healthy diet. It's not medicine. It won't cure anything. Drinking it daily is associated with modest health markers, which is also true of drinking coffee, herbal tea, or water in adequate amounts.

The catechin content is what makes green tea distinctive in flavor and chemistry, but the dose in a typical brewed cup is small enough that you shouldn't expect dramatic health effects either way.

How brewing affects catechin extraction

A few practical things worth knowing:

• Longer steeps extract more catechins. A 5-minute steep will extract more total catechins than a 60-second steep. But the extra catechins will taste bitter and may cause more stomach upset in sensitive people.
• Higher temperatures extract catechins faster but also degrade them. A 60-second steep at 160°F produces a cup with well-extracted catechins that are still chemically intact. A 60-second steep at 195°F produces a cup with more catechins but more of the bitter degradation compounds.
• Multiple short steeps preserve catechins better than one long steep. Three 30-second infusions extract more usable catechins than one 90-second infusion, with less bitterness.
• Adding lemon increases catechin absorption. Vitamin C stabilizes the catechins in the cup and may increase their bioavailability. Adding a small amount of lemon juice (or eating a vitamin-C-rich food alongside your tea) is the closest thing to "biohacking" green tea consumption.

For most people, the practical takeaway: brew at 160–170°F for 60 seconds, drink the cup, optionally re-steep once or twice. The first infusion will have most of the catechins you'll get. Don't try to extract more by over-steeping.

The takeaway

Catechins are the chemistry behind green tea's distinctive flavor and its modest health reputation. They're the reason temperature matters when you brew. They're the reason green tea tastes the way it does — grassy, vegetal, slightly astringent, with a long aftertaste that can turn bitter if you push the brew too hard.

Brew at the right temperature, steep for the right time, drink the cup. The chemistry will take care of itself.

Brew slow. Sip slow. Mind the temperature.

If you want to read more about how to put this into practice, our how to brew a proper cup of sencha post covers the home method in detail. For the broader tea-chemistry picture, our why does brewed tea sometimes taste metallic post covers another set of chemical interactions that affect the cup.