If you have leftover wine, allow it to cool to room temperature, then store in an airtight container in the refrigerator for up to three days. In fact, this is a great tactic for preparing mulled wine ahead of time. Simply prepare according to the recipe, then cool and store in the fridge for up to three days. Gently reheat on low in a slow cooker, or over medium-low heat on the stove top, about 30-45 minutes before your guests arrive.