Why doesn't mint tea taste like mint tea everywhere?

The short answer

Moroccan mint tea is Chinese gunpowder green tea with fresh spearmint and large amounts of sugar, brewed and poured from height to create froth. The ratio of sugar to tea varies by region and season. It's a prepared beverage with a specific technique, not mint steeped in hot water.

You've had mint tea before. This is not that.

Moroccan mint tea — atay nana — is not mint-flavored tea. It's a construction. Chinese gunpowder green tea (the pellets, not the leaves) is brewed strong, then combined with fresh spearmint (nana, not peppermint) and a quantity of sugar that would alarm a dentist. The standard ratio is roughly one tablespoon of sugar per glass. Some families use more.

The pouring is functional, not theatrical. Tea is poured from height — sometimes two feet above the glass — to aerate the liquid and create a thin layer of foam. The foam indicates proper mixing and temperature. The first glass is poured back into the pot and re-poured, a process repeated two or three times until the host is satisfied with the consistency. Each round of glasses — there are always three — tastes different. The first is mild, the second strong, the third sweet.

The tea you had in London or New York was probably peppermint, brewed once, with sugar optional. It's a different plant, a different process, and a different purpose. Moroccan tea is a social technology — the preparation takes ten minutes, the three rounds take thirty, and during that time you are sitting, talking, and being hosted. The tea is good. The time it buys is the point.