Preparation Place carrots in a heatproof resealable container or jar. Combine vinegar, sugar, salt, peppercorns, mustard seeds, and 1/2 cup water in a small pot. Bring to a boil over high heat, stirring occasionally. Immediately pour over carrots. Let cool to room temperature, then cover and refrigerate at least 2 hours before serving. Cooks' note:Pickled carrots can be stored in the fridge in a resealable container for up to 3 weeks.