Wintergreen Leaves are used as a flavoring agent in beer or soda. To get the flavor, wintergreen leaves must be allowed to sit 3 to 4 days until they naturally begin to ferment, then added to the brew. To do this, boil 1/2 gallon of water, pour over 1 to 2 ounces wintergreen leaves, cover, and allow to stand until fermentation begins. You can use up to two oz. of wintergreen in a five gallon batch of homemade root beer. If you are using a root beer extract as a base then you will only need to enhance the existing flavor and less can be used. 1 oz.