Mr Forsyth was managing director of human resources firm Sheffield Consulting when he bought the "piece of dirt" in 1993.
More than $2.5 million was spent on developing it - done in weekends for eight years while keeping his day job. "It would cost far more than that to do now," he said.
Helping to plant the 10,000 vines was Steve Hood, who is still vineyard manager and is described as a "magician" for getting results from soil which, though unproductive for farming, had the advantage for organic grape growing of being untouched by chemicals.
The first release of wine was in 2000 and the vineyard was the first to come under the Sustainable Viticulture wing of Winegrowers New Zealand.
Briton Hugh Johnson, reputed to be the world's best-selling wine writer, named it one of his favourite 200 wineries globally.
The food side of the business started in 2001 and Wine International magazine named it as one of the finest vineyard restaurants anywhere.
Mr Forsyth said the business had huge potential to develop further - the restaurant opened for only three days a week in winter, was not a wedding venue and the wine had not been exported. He thought the "stunning site" with its own beach, 50 minutes from downtown Auckland, would also make a "fantastic lodge".
"Today we are flat out, with 70 per cent of guests from Ireland or Australia, and we have huge bookings for the next four or five weeks from people from all over the world."
Bayleys real estate agency said the 8.7 ha estate was being sold by international tender which would close on November 9 - unless sold before.
