Water Temperature: Why Boiling Water Ruins Green Tea
Bitterness and sweetness extract at different rates. Temperature decides the balance between them.
The most common mistake in tea brewing is pouring boiling water over everything. It suits some teas and destroys others, and the difference is large enough that people conclude they dislike green tea when they have only ever encountered it brewed badly.
What Temperature Changes
Different compounds in tea leaf dissolve at different rates and different temperatures. Amino acids, particularly theanine, extract readily at lower temperatures and contribute sweetness and a savoury depth. Catechins and tannins extract faster as temperature rises and contribute bitterness and astringency.
Brewing a delicate green tea at ninety-five degrees extracts the bitter compounds rapidly and overwhelms the sweetness the leaf was capable of producing. The same leaf at seventy-five degrees produces something entirely different.
Target temperatures
- Japanese green (gyokuro). 50-60°C. Very low; emphasises umami.
- Japanese green (sencha). 65-75°C.
- Chinese green. 75-85°C.
- White tea. 80-90°C.
- Oolong, light. 85-90°C.
- Oolong, dark or roasted. 95-100°C.
- Black tea. 90-100°C.
- Puerh. 95-100°C.
Hitting the Temperature Without a Kettle
A variable temperature kettle makes this trivial and is not necessary. Boiling water left to stand loses heat at a fairly predictable rate, and a few measurements with a thermometer establish the timings for your kitchen.
| Method | Approximate result |
|---|---|
| Boil, stand 1 minute | Around 95°C |
| Boil, stand 3 minutes | Around 88°C |
| Boil, stand 5 minutes | Around 82°C |
| Boil, stand 8 minutes | Around 75°C |
| Pour into a cold vessel, then into the pot | Drops 5-10°C per transfer |
| Add a splash of cold water | Fast and imprecise but effective |
The transfer method is traditional in several tea cultures precisely because it is reliable: pouring water between vessels loses a predictable amount of heat each time.
Give someone a good sencha brewed at boiling point and they will tell you they do not like green tea. Brew the same leaf at seventy degrees and they will ask what it is.Lian Ashworth
Altitude
Water boils below one hundred degrees at altitude — roughly one degree lower per three hundred metres. At two thousand metres, boiling water is around ninety-three degrees, which changes the calculation for black teas and puerh that want genuinely hot water.
Vessel Temperature Matters
Pouring correctly heated water into a cold pot drops the temperature immediately, sometimes by ten degrees or more. Warming the vessel first with a rinse of hot water eliminates this and is standard practice in every serious tea tradition.
- Rinse the teapot or gaiwan with hot water and discard it.
- Warm the cups the same way if you are brewing small volumes.
- Add the leaf to the warmed vessel and let it sit for a moment; the aroma released is informative.
- Pour the water at the target temperature.
- For thick ceramic, allow slightly more warming; it absorbs considerable heat.
When Boiling Water Is Correct
Robust black teas, roasted oolongs, aged puerh and most herbal infusions want genuinely hot water. Under-heating these produces a thin, underdeveloped brew, and the compounds that would turn bitter in a green tea are either absent or desirable here.
- Assam and other strong black teas need heat to extract properly.
- Roasted oolongs open up only at high temperature.
- Aged and fermented teas want boiling water and often a rinse first.
- Herbal infusions, being neither leaf nor tea, generally want boiling water and long steeping.
Experiment with one tea
Take a single green tea and brew it three times at seventy, eighty and ninety degrees, keeping everything else identical. Taste them side by side. The difference is larger than most people expect and it teaches the principle permanently in about ten minutes.
Temperature and Steeping Time Interact
Lower temperature with longer steeping can produce a similar strength to higher temperature briefly, and the flavour balance differs considerably. Cold brewing takes this to its extreme: hours in cold water produces a sweet, low-bitterness infusion from leaves that would be astringent brewed hot.
This is why cold-brewed green tea is so approachable, and it is a useful technique for teas that have proved difficult to brew well hot.