In rare good news for grape growers, last week's heatwave was expected to burn up to 15 per cent of local grapes but was thwarted by timely rainfall, reducing the estimated damage to between 1 and 5 per cent.

Peter Baratto of Baratto Wines expected his grapes would have been slightly sunburnt last week but the fallout from the worst frost in 50 years was of much greater concern.

"Amongst the older vines on my property, I can walk for 20 metres and there isn't one bunch sitting on the vine," Mr Baratto said.

"I know one farmer who has stopped harvesting already because the fruit isn't there and another farmer who is harvesting less than a tonne-and-a-half per acre," Mr Baratto said.

"Another major concern is big bunches of red wine varieties without seeds in them, which people are telling me will ripen but I can't see happening."

Mr Baratto said he wouldn't know the full extent of the damage until he started harvesting himself but said he would be lucky to pick just one quarter of his semillon, trebbiano and merlot grapes.

Bad sunburn during last week's heatwave was expected to complete a debilitating trifecta for grape growers, who had already suffered through black frost and hail, but the grapes performed better than expected.

"We thought up to 15 per cent of the region's grapes could have been sunburnt but people kept irrigating, we had some rain to boost subsoil moisture and the hot weather came on slowly letting the grapes adjust," Riverina Wine Grapes Marketing Board (RWGMB) chairman Bruno Brombal said.

"Fortunately the heat won't really hurt the quality of the fruit, the fruit quality should remain excellent.

"The ideal weather for the rest of vintage is around 25 to 35 degrees without anymore rain."

Mr Brombal said this week's heatwave was worrying but the grape quality would not suffer unless the mercury hit 44 degrees.