An American scientist has sparked a trans-Atlantic tempest in a teapot by offering Britain advice on its favorite hot beverage.

Bryn Mawr College chemistry professor Michelle Francl says one of the keys to a perfect cup of tea is a pinch of salt. The tip is included in Francl’s book “Steeped: The Chemistry of Tea,” published Wednesday by the Royal Society of Chemistry.

Not since the Boston Tea Party has mixing tea with salt water roiled the Anglo-American relationship so much.

The salt suggestion drew howls of outrage from tea-lovers in Britain, where popular stereotype sees Americans as coffee-swilling boors who make tea, if at all, in the microwave.

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The U.S. Embassy in London intervened in the brewing storm with a social media post reassuring “the good people of the U.K. that the unthinkable notion of adding salt to Britain’s national drink is not official United States policy.”