Boiling Water Doesn't Ruin Green Tea. Timing Does.

Boiling water does not ruin green tea, though it changes what ends up in the cup. A 2026 study in LWT brewed eight teas at 80, 90 and 100°C and found that four of the five green teas released more catechins in fully boiling water than at any lower temperature. The astringent compounds were not destroyed at 100°C. They simply arrived first: in green tea they reach 63 percent of equilibrium in 4.5 to 7.9 minutes, while free amino acids need 8.3 to 25.

What the Study Actually Did

Researchers at the Shanghai Academy of Agricultural Sciences brewed eight cultivars — five green, two white, one black — at a fixed 1:50 ratio for five minutes at 80, 90 and 100°C, then measured 32 compounds by UPLC-MS/MS: five catechins, 19 free amino acids and eight phenolics. A second run at 90°C sampled the same infusion at 1, 3, 5, 7, 10, 20 and 40 minutes to build dissolution curves. A third covered three consecutive infusions. Each cultivar was a single batch in three biological replicates.

What the Numbers Show

At 90°C for five minutes, the green infusions carried 626 to 1,148 mg/L of catechins. The two white teas and the black tea stayed below 200 mg/L.

Most of that spread was settled before the water arrived. Green samples held 21,800 to 119,138 mg/kg of catechins in the dry leaf; the white and black samples held 468 to 12,801. Processing is not neutral either: catechins rose 6.4- to 93.6-fold during green tea manufacture and fell by roughly 80 percent during black tea manufacture.

The more useful finding is the timing. Phenolics reached 63 percent of equilibrium in 2.9 to 8.5 minutes. Green tea catechins got there in 4.5 to 7.9. Free amino acids needed 8.3 to 25, and catechins from the white teas took 22 to 25. In one cup, under one temperature, the astringent fraction finishes its work while the savoury fraction is still getting started.

Where the Old Advice Is Wrong

The familiar instruction is that green tea wants 75 to 85°C, and that boiling water burns the leaves into sharp bitterness. Nothing burns at 100°C and nothing is scorched; the leaves do not cook in any sense a chemist would recognise. What changes is the rate at which classes of compounds leave the leaf.

The advice is not foolish. Catechins are fast and astringent, so hot water plus a long steep does give a rougher cup. The habit works; the mechanism was wrong. The mechanism matters because it says which dial to turn. If leaves were being burned, temperature would be the whole story. This is an extraction race, so time moves fastest.

A five-minute steep at 100°C and a forty-five-second steep at 100°C are not the same tea, though the thermometer reads the same.

Two Exceptions and One Condition

Mao Feng, the Anhui green, peaked at 90°C and fell significantly at 100°C. Mei Zhan, processed as a black tea, peaked at 80°C. The authors attribute the decline to possible thermal degradation or epimerization — a possibility raised rather than a mechanism demonstrated.

The condition is the method. Everything here was measured at 1:50 for five minutes, closer to a tasting bench than to a gaiwan. Gongfu brewing with ten-second infusions never reaches the later part of those curves. The data explain why short, hot infusions taste cleaner; they do not say a gongfu session needs 80°C water.

How We Brew Green Tea Here

The following is our practice, not a finding from the paper. We brew Huangshan Maofeng at about 90°C, where the study's Mao Feng sample peaked. Longjing and other flat or bud-heavy greens we keep at 85 to 90°C and pour fast. To use water straight off the boil, we pour into a room-temperature cup first, then onto the leaf, and cut the infusion to 10 or 15 seconds.

The first infusion does most of the work: the Longjing sample carried 49 percent of its catechins, 58 percent of its amino acids and 60 percent of its phenolics in the first steep. Going thin by the third infusion is normal, not a flaw in the tea. For the step-by-step method, see our green tea brewing guide.