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With ice wine, what’s the motivation for having the grapes freeze?
I recently brought some ice wine, which I understand is made from frozen grapes, back from Canada. What’s the motivation for having the grapes freeze?
Ice wine, as you no doubt noticed, is very sweet. That’s where the frozen grapes come in. As water freezes, the ordered pattern of molecules that make up ice tends to push impurities like sugar into the more disorganized liquid part. You may see a similar phenomenon in your ice cube tray; the cubes often look cloudy in the center. This is due to the water freezing at the edges first, pushing the impurities (mostly bits of dissolved air) toward the center.
Incidentally, this basic process is of practical significance. Silicon for the semiconductor industry is purified using this phenomenon; without it there would probably be no affordable consumer electronics.
But back to ice wine. It has caught on recently but is really a rediscovery. Pliny the Elder, who lived between 23 and 79 AD, wrote about grapes that were not harvested until after the first frost. But people lost interest in this kind of wine until 1794 in Germany. Today, Germany and Canada are the largest producers of ice wine.
There is another way to get sweet grape juice to ferment: Let a fungus attack the grapes, turning them into something akin to a raisin. As the grapes dry, water evaporates, but the sugars remain, making the grapes sweeter. The fungus that does this without wrecking the taste of the grapes is botrytis cinerea, often called noble rot. Wine made from such “rotten’’ grapes, called botrytized wine, dates to the late 1500s in Hungary.
This article originally appeared on boston.com's "Ask Dr. Knowledge" segment on December 27, 2010.
Interesting article
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