Johnson, who was then told that alcohol was against the Sikh religion, made his comments when speaking about whisky exports to India during an address at a gurdwara in Bristol, southwest England.
Wearing an orange turban, Johnson said whisky exports would get a boost if Britain and India could strike a trade deal.
"Whenever we go to India... we have to bring 'clinky' in our luggage. We have to bring Johnnie Walker. We have to bring whisky because as you may know there is a duty of 150 per cent in India on imports of Scotch whisky," he said.
"So we have to bring it in duty free for our relatives. But imagine what we could do if there was a free trade deal with India," he said, according to a video published online by the Bristol Post newspaper.
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But one worshipper, speaking during a subsequent question and answer session with Johnson, said she would be against increasing whisky exports to India because "it's against our religion".
"No way am I going to vote Tory because I don't want alcohol. I'm a practising Sikh and to me that is completely outrageous," she said, adding: "It's causing a lot of problems at the moment."
Johnson apologised and said: "I understand your point of view."
Britain's Sikh Federation also voiced outrage.
"No politician in his right mind would speak in a Gurdwara about a trade deal involving alcohol," the foundation's head Bhai Narinderjit Singh.
"It is a requirement that Sikhs should not consume any intoxicants. Boris Johnson should know much better. After all he is the foreign secretary," he said in a statement.
Johnson, a former mayor of London who was once seen as a possible future prime minister, has been sidelined in the Tory party's campaign so far ahead of a general election on June 8.
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