Staff members at a Maliandao store pack the just-arrived Xihu Longjing tea into small bags. [Photo/CFP]

Some of us are startled to learn that green teas have more caffeine than any others. It's the freshest, she explains, and it's not aged or fermented. While those processes can make the tea leaves darker and their taste "stronger", she adds, it dissipates the amount of caffeine.

"That's why most of your Chinese friends probably drink green tea first thing in the morning－and never late in the day," Han says. "If you drink green tea in the evening, you are going to be up all night."

By the time we finish at our second tea vendor, where we sip our third and fourth pots of tea, we suspect we could be up for the next two nights. Han introduces us to two white teas－one with a grand aura of mushrooms and the other with a nose like fresh grass－and we all get up with a bit of a buzz. The aftertaste in my mouth is almost metallic.

"That's why we take our lunch break in the middle," says Han, who runs these tours every other Sunday through The Hutong, an education center with lots of programs that introduce foreigners living in Beijing to different aspects of Chinese culture.

"We used to visit all four tea shops before we ate," she tells us as we dig into a platter of saucy barbecued eggplant. "But some people were almost too dizzy to walk to the restaurant after drinking so much tea. So now we break things up a little."

A grateful murmur ripples around the table.

"So much tea is a little overwhelming," says a German woman in our group who has been in China for just three months. "If we had to do more before lunch, I think the tastes would all run together in my mind and I wouldn't remember one from another."