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1.BEFORE: Frozen Chardonnay grapes from Fraser Gallop Estate in between the chilling process and pressing.

Before: Frozen Chardonnay grapes from Fraser Gallop Estate in between the chilling process and pressing.

ICED wine styles are developing an enthusiastic following in Australia, with Iced Riesling, Cabernet and Chardonnay competing for the luxury dessert wine market. But with temperatures here unable to emulate the freezing conditions in the northern hemispheres where ice wines are traditionally made, Danielle Costley writes our winemakers are chilling out with alternatives.

The first Australian Iced Riesling made its debut in 1995 and was pioneered by Tasmania’s Andrew Hood under the Wellington brand.

Over the years this dessert wine developed a small, yet loyal, following so when the winery was sold to Frogmore Creek it is no surprise the new owners resurrected the Iced Riesling under the new label in 2004.

Since then, this Coal River Valley winery has expanded its dessert range to also include an Iced Gewurztraminer in 2010 and 2011.

With night temperatures in Australia not being cold enough to freeze grapes on the vine, Frogmore Creek has developed a cryo-extraction freezing technique that can adapt to the country – and the climate.

According to Frogmore Creek’s Alain Rousseau, the success of the cryo-extraction process relies upon using grapes that are ripe and ready for wine making. This is because perfectly ripe grapes will have a higher sugar content than grapes that still need to ripen.

Consequently, the truly ripe grapes will freeze more quickly and the juice from the frozen grapes will have a greater concentration of sweetness and flavour.

“As our climate doesn’t allow for the natural freezing of grapes on the vine, we harvest the fruit with the highest sugar content (around 14 baumé),” Rousseau said.

FREEZE CONCENTRATION

Once the grapes are picked and cleaned, they are placed in a freezing tank with floor jackets that is directly connected to the compressor to freeze the grapes.

“We then start a freeze concentration of the juice in special tanks. It takes four to five days to have the tank full of solid ice,” he said.

“After that, we pump the concentrated juice through the bottom valve. This operation takes a few days as the sugar is quite thick and it takes time to run down through the ice block,” Rousseau explained.

“We then press the grapes as soon as possible and settle the juice in a tank. The juice is kept for a few days as clear juice, with no lees, at a low temperature to avoid the start of fermentation. The sulphur is kept around 20 mg/litre of free sulphur.”

The chilled liquid is then drained from the wine press, while ice crystals usually remain in the press.

This process is understood to produce the highest level of concentrated flavour in the liquid that is pressed from the grapes.

The juice has to be at 17.5 to 18 baumé before the start of the fermentation. Sometimes, it takes two concentrations to access the desirable baumé level.

The operation concentrates all parts of the juice: sugar, acid, flavours and sulphur. Rousseau said this was why the operation has to be done as soon as possible to avoid getting a level of total sulphur above legal requirement.

Full story in the May issue of Grapegrower & Winemaker.

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