Place radishes6 in a small bowl. Bring white wine vinegar¾ cup, sugar3 tablespoons, red pepper flakes1 teaspoon, ½ tsp. salt2 teaspoons, and ¾ cup water to a simmer in a small saucepan over medium-high heat and cook, stirring occasionally, until sugar is dissolved, about 5 minutes. Immediately pour brine over radishes and let cool. Cover and chill at least 2 hours.