Natural ice wine can only be made when ripe grapes undergo what is known as a ‘hard freeze’. This happens at around -7°C (19 °F), but should be slightly colder depending on the amount of time needed to get the grapes to the press after picking. At these temperatures, sugars and other dissolved solids inside the berries do not freeze.
This is how the Riesling grapes from Weingut am Stein in Franconia, Germany were packed for protection in 2016 and left to wait for freezing temperatures.
Healthy grapes are left to hang on the vine for months following the normal harvest. If a freeze takes too long to come on, the grapes will rot and can no longer be used. If the cold is too severe, no juice can be extracted.
Grapes for ice wine are usually harvested in the coldest, darkest hours of the night in order to ensure that they stay frozen until they reach the press.
Can you imagine?
Your alarm goes off at 2am and you head out to the vineyard in the freezing cold with a head lamp and a pair of scissors. The ground is frozen cold and slippery, but you have to hurry! When the sun comes up the grapes will start to thaw and it will be too late to press them.
The separation of frozen water from the rest of the juice is what makes ice wine so concentrated and sweet. Only about 10-20% of the liquid inside of each grape is used – the rest remains frozen solid and is separated out in the press. Because the juice is so sweet, fermentation can take 3-6 months. The final product will have between 160-220 g/L of residual sugar and an ABV of around 10%.
The most common grapes used to make Ice Wine are Riesling, Gewürztraminer, Vidal Blanc, Grüner Veltliner, Chenin Blanc and even the red wine grape, Cabernet Franc.
The main countries of production are Canada, Germany, Austria and the USA.