Cellar Door, part of The Sydney Morning Herald NSW Food and Wine Festival, presented by Citi, is a chance for winemakers across the state to showcase their best. But for some the timing has been all but ideal.

Harvest has arrived early this year and some winemakers have had to choose fermentation over festival-going.

"You only get one chance a year," said Ken Helm, owner and director of Murrumbateman-based Helm Wines.

"This is the first time we have ever harvested riesling in February."

Mr Helm has been a regular participant in the NSW Food and Wine Festival but because this year's harvest has been the earliest in his 41 years as a winemaker, he has had to take a rain check.

Jacob Stein, a third-generation winemaker at Robert Stein Winery in Mudgee, will make it to Sydney Cellar Door, but said the early harvest had broken a 40-year record.

Mr Stein started harvesting his gewurztraminer, a white wine grape, three weeks earlier than usual.

Scientists predicted earlier grape harvests several years ago when a team from the CSIRO and the University of Melbourne found that vintages were moving forward by 0.8 of a day each year.

Professor Snow Barlow, a viticulture expert from the University of Melbourne, was co-author of the study that looked at how climate change is affecting vineyards around the country.

He found that over 25 years, harvest had moved about 20 days earlier.

"People have seen it in France and other areas around the world too," he said.

Though some of the effect might be due to better disease control and improved crop management practices, the major factor was found to be warmer temperatures.

Winegrowers are on the front line of global warming and, according to Professor Barlow, you'd be hard pressed to find a climate change sceptic among them.

Compressed vintages, where several grape varieties ripen in quick succession, are creating logistical challenges.

Wine barrels from France are still in containers at sea, slowly chugging towards Australia.

"I'd love to have the barrels here this week and put my chardonnay straight into them, but unfortunately we'll have to wait," said Tom Ward, owner of Swinging Bridge Winery in Orange and president of NSW Wine.

And grape pickers are now working in 33-degree heat compared with the usual 25-degree March days.

But as Ken Helm put it, "Winemakers are pretty smart these days."  There aren't any sour grapes in this hardy bunch.

Tom Ward has moved some of his vines to higher ground in Orange, in an effort to keep getting the best-quality wine.  And Ken Helm is thinking about relocating grapes from his vineyard, which is 580 metres above sea level, to a cooler site at 800 metres.

Winemakers are also experimenting with different grape varieties.

Jacob Stein thinks tempranillo, a Spanish variety suited to warm Mediterranean climates, might be Mudgee's next big thing.

"I've got high hopes for this variety," he said. "It's exciting, and we have to keep evolving."

Though earlier harvests present challenges, winegrowers from Mudgee to Orange are adamant this year's vintage is one of the best ever.

And Ward is confident our state's winegrowers are well equipped to adapt to changes.

"It's a conversation we've got to have, but is it threatening the viability of our industry? Absolutely not," he said.

Sydney Cellar Door kicks off at 4pm on Friday, February 27, and will run until 6pm on Sunday, March 1.