(VinePair) - Ever wonder how dessert wines become sweet? It’s easy to imagine a bunch of winemakers just opening up big vats and pouring in some granulated sugar. (That is, after all, what makes bran flakes palatable for all those prepubescent years.) And while some liquors have shown evidence of actually having sugar added, dessert wines become sweet by a variety of processes.

They also become expensive by a variety of processes. The reason that most dessert wines come in half, or 375 mL bottles, is because the basic concept is dehydration—meaning you get less juice per grape, and it takes a lot more to fill a bottle. But considering what goes into most dessert wine (especially extremely careful timing of harvest), you’ll tend to find a consistency of quality, if also a consistency of price. And don’t—really—let the “sweetness” factor scare you off. Highly aromatic and high acid grapes tend to go into dessert wines to create balance with the sweetness, not to mention concentrated complexity. And then there’s Noble Rot, which just makes everything delightfully funky.

Fortification

As far as sweet wines go, this is a pretty simple one to tackle. Take port. Like any other wine, port is fermented by allowing yeasts to feast on sugar and convert it to alcohol. However, where wines like a Cabernet do this to the point of a much dryer wine, the fermentation of port is actually stopped—like, brought to a screeching halt, by the addition of a neutral spirit. This is called fortification. (Thus, fortified wines.) Fortification has two important effects: it ups the alcohol content of the wine—which is why we sip port in those tiny adorable cups—and it stops fermentation, meaning there will be leftover sugar. And that’s what makes port sweet.

Noble Rot

Even if you haven’t had the pleasure of drinking a wine affected by Noble Rot—the fancier name for Botrytis cinerea—you’ve probably heard of it. It’s actually just a mold that basically raisinates the grapes, drying them up and concentrating their sugars. Not that it only intensifies sweetness; by dehydrating the grapes, Noble Rot also concentrates the flavors, yielding richly aromatic, intense, low-yield dessert wines like Sauternes, Tokaji Azu (from Hungary), and Spätlese Riesling.

Ice Wine

By this point you’re seeing the pattern—it’s all about reducing the amount of water in the harvested grape. And the ice wine process is a really cool way of doing that. Also, yes, a freezing one. The idea is leaving the grapes (typically high aromatic, decently acidic grapes) on the vine into the winter. By picking them at just the right time—and that’s a seriously important decision on the vintners’ part—enough of the water is still frozen, so when you press, you get concentrated sweetness and aromatics.