By 1984, Coke's lead over Pepsi had dropped to 4.9 per cent and in supermarkets "America's Favourite Drink" was in danger of becoming its second favourite.
Many young people of all ages seemed happy to be labelled the "Pepsi Generation". And most damning of all, in blind taste-tests, a majority preferred the rival cola, even if it wasn't "the Real Thing".
To the top brass in Coca-Cola management, there seemed only one solution: to rewrite the hallowed recipe.
And so it was that on April 23, 1985, after spending $4 million on market research, the company took Old Coke off the shelves and replaced it with New Coke. The response was immediate and deafening. Consumers might have preferred the new flavour in some blind tests - preferred it to Pepsi, even. But was that the same as wanting change?
With 40,000 angry letters and 6,000 indignant telephone calls a day, Coca-Cola now knew the answer. Meanwhile, Americans wanted their Old Coke back. Black marketeers scoured the world for remaining cases, and one man delivering the new product was physically assaulted. "I couldn't have been more surprised if someone had told me I was gay," wrote one customer.
Another complained: "When they took Old Coke off the market, they violated my freedom of choice. We went to war in Japan over that freedom."
Old Coke stalwarts even tried to file a class action law suit against the company. Clearly something had to be done to restore public confidence. And for once, there was no doubt as to what that something ought to be. After just 87 days, New Coke was scrapped and Old Coke reinstated.