Tannins, caffeine and colour compounds don't flood out of a teabag all at once — they diffuse out of the leaf matrix over time, fast at first and progressively slower as the leaf's easily-reached surface material runs out, approaching a maximum the same way a hot drink approaches room temperature. That's genuinely the same mathematical shape as Newton's law of cooling, and it's why "one more minute" matters far more early in the brew than it does after five minutes have already passed.
Published extraction studies find CTC (crush-tear-curl) teabag tea reaches roughly 95% of its maximum strength by around 7 minutes. A standard teabag in a 200ml mug brewed for 3 minutes sits at about 72% strength — a genuinely different cup than the same tea left for 5, at 88%.
Teabag tea is typically CTC-processed — crushed, torn and curled into small fragments with far more exposed surface area than whole or lightly-broken loose leaves. More surface area means faster diffusion, which is exactly why this tool uses a slower rate constant for loose leaf.
Not the rate — but it raises the ceiling. More tea relative to the water means more extractable material available, so the same brew time reaches a darker maximum, even though the underlying diffusion rate per leaf fragment is unchanged.
Colour is what you actually judge a cup by — this tool solves the extraction equation backward, working out exactly how long your specific tea amount and mug size need to reach the shade you tapped, rather than you guessing at a generic "3 minutes" that assumes a specific ratio.
Not the brewing, no. Milk goes in after the leaves are out, so it cannot slow or speed up extraction. What it does do is dilute what you end up drinking, and by more than people expect: a 30 ml splash in a 200 ml mug takes 13% off the strength, and a proper builder's 50 ml takes 20%. The strength readout shows both figures once you add any — what came out of the leaf, and what is actually in the cup.
That extraction is first-order: the rate depends on how much is still left in the leaf, so it starts fast and tails off. That is why half the strength arrives in the first 97 seconds and the remaining half takes five and a half minutes — and why "leave it a bit longer" does less than you would think.
There is no temperature anywhere in this model, which after time is the strongest
lever there is: the same curve serves a boiling black tea and an 80 °C green one,
and in reality the cooler brew is markedly slower. Also absent: agitation, water hardness,
leaf grade beyond bag-versus-loose, and a second steeping. And strength is not bitterness
— tannins come out more slowly than caffeine does, which is why a long brew is not
simply a strong one. Verified in tea_model.py.
Releases in which this page changed, newest last. Derived from the archived copy of every release, not from notes written afterwards — so it reflects what actually shipped. Site-wide passes are left out; they are in the full changelog.