I assume you are concerned about/for fermentation of the sugars. At 20% alcohol this is not ever going to be a concern in the freezer or refrigerator; it will keep for years. (Yes, I have done this.) At room temperature, there won't be fermentation either but you might experience some off-putting odors from oxidation of the sugars, over a few months, and I doubt even this will occur. Wino recommends that drinking 'the damn stuff' is the 'best practices' procedure.