When you are ready to defrost the frozen eggnog, you should move the container from the freezer to the refrigerator and let your eggnog thaw overnight. Avoid thawing eggnog by letting it sit at room temperature. Leaving frozen eggnog at room temperature will cause the ingredients to break down, leading to a lumpy, all-around unpleasant consistency. Leaving thawed eggnog sitting out for too long can also cause the eggnog to go bad due to the drink's egg product. Keep in mind that separation may occur after you thaw eggnog. You can fix separation issues by shaking the eggnog well or using a blender to blend the ingredients better. You can serve eggnog cold or hot. If you want to warm defrosted eggnog, you can either heat it for a few minutes in the microwave or reheat it in a pot on a stovetop over medium heat.