I published this post in May of 2012, but since as of late a) a friend of mine found it while she was researching Eiswein, b) this was an early post so chances are many of you have not seen this, and c) it was -20 degrees Celsius (-5 degrees F) last night up here in Alaska, I thought it was a good time to republish this post. I hope winter is treating you all well!
There is a magic aura that surrounds German ice wine (“Eiswein” in German), especially the Rieslings. It is rare, it is expensive, and to me, it is more syrup than wine. German ice wine can only be harvested when it is -7 degrees Celsius (19 degrees F). This often only happens in December or January, which means the winemakers have to leave the grapes on for way after the usual harvest. If it does not get that cold, then the grapes will be lost, same is true if birds feed on them, which is why most now put some sort of net or plastic around the vines that carry the grapes. Other countries have resorted to collecting unfrozen grapes and then freezing them to produce ice wine. It takes away from that whole magic, and the grapes are not as weathered as they are in German ice wine.

Grapes protected by plastic in Karl Erbes vinyards.
(Photo from Karl Erbes website at weingut-karlerbes.de)
The winemakers watch the weather and temperature forecasts nonstop to ensure that they are ready to go when the temperatures are right. They then venture out and harvest the grapes, bringing them back as soon as they can, because it is vital that the grapes remain frozen when they are crushed. The harvest itself usually produces stunning photos (as you can see), often it happens in the early morning hours. The grapes need to be of at least Beerenauslese level in sweetness. Check this post for what that is…
Because the water remains mostly frozen in the grapes, the little juice that is coming out is highly concentrated. The levels of sugar and acidity are very high, which makes these wines so interesting. Once the grapes have been crushed, the fermentation process needs to get going, which is not the easiest thing to achieve at such low temperatures. A friend of mine once told me about the small heating fans he surrounds the juice with in order to get things started…

Carrying the grapes in the traditional bucket
(Photo from Karl Erbes website at weingut-karlerbes.de)
The outcome is intense, intense wines. They are usually bottled in half bottles, and command a premium price. In the steep hills of the Mosel river, harvesting is done by hand. If you see a cheap(er) ice wine (usually from Rheinhessen or Baden), that usually means that they were machine harvested, which cuts the labor price and therefore their bottle price. It takes away part of the myth, though…
Ice wines age incredibly well, and are good for decades, sometimes centuries. In their first years, they are almost overbearingly intense: the sweetness of the sugar, raging acidity on your tongue, it can be mindblowing. With age, they mellow out more, and that is when their true beauty shines. I can never drink more than a small glass in one go, but I think that is a good thing. Ice Wine is meant to be shared, and enjoyed at very special occasions, because they are very special indeed.
Update 12/12/2012: Check out the video of an ice wine harvest here!