Do tannins cause tea stains on cups and teeth?

Yes, tannins are largely responsible for the brownish stains tea can leave on mugs and teeth over time, similar to how red wine stains a glass.

Does milk really reduce astringency?

Many people find it does — the proteins in milk bind to some tannins, which is part of why milky black teas taste smoother than the same tea brewed strong and black.

Are tannins the same as caffeine?

No, they're entirely different compounds. Tannins affect texture and astringency, while caffeine is the stimulant. A tea can be high in one and moderate in the other.

Tea Education

Tea Tannins Explained: The Source of Astringency

That dry, puckering feeling from over-steeped tea comes from tannins. Here's what they are and how to keep them in check.

6 min read Updated 2026-08-05

Dark, over-steeped black tea in a glass cup showing a strong reddish color

Key takeaways

Tannins (mainly catechins in tea) are plant compounds responsible for astringency, that dry, puckering feeling.
Longer steeps, hotter water, and more leaf all extract more tannin, not just more flavor.
A little tannin gives tea structure and body; too much makes it taste harsh and bitter.

What tannins actually are

In tea, the term 'tannin' is used loosely to describe a group of polyphenols, mainly catechins in green tea and their oxidized cousins, theaflavins and thearubigins, in black tea. Chemically they're related to the tannins found in red wine and unripe fruit.

They're responsible for the dry, mouth-puckering sensation called astringency — the feeling, not really a taste, that makes your tongue feel slightly rough after a strong cup.

Why over-steeped tea tastes harsh

Tannins extract more slowly than the compounds responsible for aroma and sweetness, so a short steep captures mostly the pleasant notes. Leave the leaves in too long, brew too hot, or use too much leaf, and tannins flood the cup, tipping it from balanced to bitter and drying.

Tea Education: Dark, over-steeped black tea in a glass cup showing a strong reddish color — Dark, over-steeped black tea in a glass cup showing a strong reddish color

Controlling tannin in your cup

The good news is tannin extraction is very controllable once you know what drives it.

Lower the water temperature for delicate teas like green and white
Shorten the steep time rather than adding more leaf to compensate for weakness
Remove the leaves or infuser once the steep is done — don't let them sit
Add a splash of milk, which binds to some tannins and softens the dry feeling

Tannins aren't all bad

A moderate amount of tannin gives tea its structure and 'grip' — the difference between a thin, watery cup and one with real body. The goal isn't to eliminate tannin, just to keep it in balance with sweetness and aroma.

Frequently asked questions

Do tannins cause tea stains on cups and teeth?: Yes, tannins are largely responsible for the brownish stains tea can leave on mugs and teeth over time, similar to how red wine stains a glass.
Does milk really reduce astringency?: Many people find it does — the proteins in milk bind to some tannins, which is part of why milky black teas taste smoother than the same tea brewed strong and black.
Are tannins the same as caffeine?: No, they're entirely different compounds. Tannins affect texture and astringency, while caffeine is the stimulant. A tea can be high in one and moderate in the other.

About the author

Written by the Leaf & Steep editorial team. We brew, weigh and re-test everything we publish at home with ordinary kitchen equipment — no lab, no sponsorships influencing the verdict. How we test.

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