Summer is critical for the Hunter’s wine growers. Grapes begin to ripen and the first batches of the region’s celebrated sémillon are picked but the volatile weather can make or break a vintage. 

Moorebank Vineyard’s winemaking controller Ian Burgess said grapes were resilient, particularly to heat, but the scorching temperatures posed unique challenges.

“When it gets hot, well the vines are clever,” he said.

“They’ve been here a lot longer than we have.”

Mr Burgess said the vines’ stomata, cells that regulate water loss, would close in the heat to retain moisture. A biological shield initially developed to survive in the Mediterranean heat.  

“It’s like having a window open,” he said. “When there’s a nice, cool breeze you open a window but when it’s too hot, you close it to keep the heat out.”

But the industry won’t be leaving it up to genetics. Mr Burgess said vineyards had erected sunshades to protect the grapes.

“They’re like humans, they can have their skin burned,” he said.

“If you end up with dehydrated fruit the flavour moves toward that raisin-like quality. You don’t want that if you’re having oysters or seafood. You want that citrus flavour, that refreshing acidity.”

The irrigation tactics will also change. Watering the vines in the midday sun leads to rapid evaporation, moisture trapped in the canopy and the potential for fungal spores to develop. 

“Rain is good, but we’ll be watering at night,” Mr Burgess said.

“There’s less evaporation, less exposure to spores and generally more control over the microclimate around the vines. It’ll also help us conserve our water.”

For most farms the heat is problematic, particularly if it means rain and water supplies are disrupted. But for winemakers it’s more complicated, but Mr Burgess is reading the forecast with positivity.

“The first sémillon are often picked on Australia day,” he said.

“We want those warm, sunny days. It’s just the spikes in heat we don’t want. But it looks to be developing as a superb vintage next year.”