It's a grey, clay-based sunscreen - and it's the latest weapon being used by Hunter winemakers to combat baking temperatures at harvest time.

And it works a treat.

"Absolutely it does, it's really effective," Bruce Tyrrell of Tyrrell's Wines explained.

"A bit like 50-plus on humans.

"We put sunscreen on our kids, so why not on our grapes?"

The big question, of course, is does it have a taste or impact on the flavours in any way.

"No, not at all," Mr Tyrrell said. "It's totally neutral.

"We spray it on, the grapes will go a bluey-grey which looks a bit odd at first, and that's it. We don't even have to wash it off. It's flavourless and after spraying it's business as usual."

Mr Tyrrell said sunburnt grapes is the greatest enemy winemakers can have.

"It's awful, and there's not a damn thing you can do about it," he said. "It has this burnt sugar taste, bitter toffee ... it's a horrible character to have."

With the Hunter now regularly seeing temperatures soar into the 40s over January and February - which happens to coincide with grape harvest in the Hunter - protecting the grapes from the heat is more important than ever before.

The other tactic winemakers and vignerons are using is to leave the leaf canopy to grow longer on the western side of vines to give the grapes some shade protection from the baking afternoon sun.

"Years ago we would never have dreamed of doing that," Mr Tyrrell said.

"It wasn't necessary, but as winemakers we're adapting to the current conditions. You have to.

“Mind you, some of the old time winemakers would be turning in their graves if they heard about it."

Which brings us to the crunch question: how is the vintage shaping up in the wake of the recent spike in temperatures?

“Everything we have picked so far has been really good,” Mr Tyrrell said. 

“We have the verdelho in and all of our top chardonnays are in – they look sensational.

“We’ll probably start on the reds next week. But if I had my wish it would be for two inches of rain in a hurry. That would be ideal.”