In Chapter 2 of "Stringing Tea," I describe how a film crew I was working with had to redo a shot of tea being brewed after the tea came out too dark. In our haste, we had just-boiled water poured directly onto the tea leaves. The tea grower who was doing the actual pouring wanted to cool the water first, but we were in a hurry. And besides, we weren't actually going to drink the tea — just film it being brewed.
After the tea came out too dark to film, the grower explained that it was because the water had been too hot.
(In other words, what we thought would be a time-saving shortcut — not cooling the water first — ended up costing us time. There's a valuable life lesson in there somewhere.)
But water that's too hot doesn't just ruin the color of tea: By essentially cooking the tea leaves, overheated water also spoils the tea's flavor and aroma.
The ideal water temperature range for brewing green tea is between 70 and 80 degrees Celsius, or 158 to 176 degrees Fahrenheit. Different teas do better with different temperatures, but if you're new to green tea, a good starting point would be roughly 75 degrees Celsius (167 degrees Fahrenheit).
Since water boils at 100 degrees Celsius (212 degrees Fahrenheit), just-boiled water is way too hot for green tea. It has to be cooled a bit first (hence the Britishism "Walk the kettle to the pot," meaning "Wait a bit before pouring boiled water into the teapot.")
But there's no need to break out a thermometer and a stopwatch when boiling water for tea. Instead, I've found that if you pour just-boiled water — from an electric kettle, say — into a Japanese-style yuzamashi (see the pictures below), then wait a couple of minutes, it will be well within the ideal temperature range.
A typical yuzamashi. The wide mouth provides a large surface area, for rapid cooling of boiled water.
Note that I intentionally used the vague phrase "a couple of minutes." This doesn't mean "precisely 2 minutes"; it means "a couple of minutes" — in other words, what you intuitively judge to be a couple of minutes, which I have found to be about as long as I can keep something in mind while doing something else. Any longer than this, and I forget the water altogether and it gets too cold.
This is yet another example, Grasshopper, of how brewing tea is an art, not a science.
Another cooling option is walking the kettle to the pot, but the problem with this is that it takes a lot longer than a couple of minutes for water to cool in the kettle in which it was boiled. It's not the waiting that's a problem, it's the forgetting.
Instead of a Japanese-style yuzamashi (which literally means "water-cooler"), you can also pour boiled water into another teapot (other than the one in which you've put your tea leaves) or something else that's easy to pour from. Avoid using an empty mug, because I've found that it's almost impossible to pour from a cup or mug without spilling.
If you've discovered Mellow Monk Green Tea, you're already three-quarters of the way to The Perfect Cup of Tea. But to make it the rest of the way requires good water at the right temperature.
But the good news is that with a little practice, you'll get there quickly. Brewing green tea is, as I've said, an art, not a science. And it's definitely not rocket science.
A yuzamashi in action. Never pour just-boiled water directly onto green tea leaves!