Sweet wines have a bad reputation in the United States as cheap, watered-down alternatives to the more refined, dry styles. Keep your sticky white zins to yourself, I thought when I began getting interested in wine. I'll drink my zippy sauvignon blancs and tannic cabernets. But then I discovered the wine that changed my mind: on a visit to South Africa's Glen Carlou Wine Estate, I tasted through their portfolio, which included a sweet wine made from 100 percent chenin blanc grapes. I was hesitant when they handed me the glass, but rather than the cloying sweetness I anticipated, I found a surprise instead — a purity of flavor that I had never before experienced, one that the sweetness itself enabled.