Warren Buffett never bets against the US, the country where he built his fortune. “The record of American business has been extraordinary?.?.?.?We are lucky — gloriously lucky — to have that force at our back,” he wrote in his annual letter to Berkshire Hathaway shareholders on Saturday.

He should have been less patriotic about Kraft, the processed food group that makes staples such as Kraft Macaroni & Cheese and Velveeta, a bright yellow “processed cheese product”. The merger that he engineered between Heinz and Kraft in 2015 has turned out very badly: Heinz paid too much for an indigestible bunch of ageing brands in the wrong country.

The $15.4bn impairment of Kraft Heinz assets that contributed to a plunge in its share price on Friday can be put down to various causes — cost-cutting by 3G, the private equity group that manages it, discounting by supermarkets and changing tastes among millennials. But there is a simpler explanation: 98 per cent of Kraft’s sales before the merger were in North America.