Yes, almond milk can go bad. You can tell that it's no longer good if it's curdled, fully separated, or tastes overly bitter or acidic. Store in the refrigerator to keep it fresh the longest. For store-bought almond milk, do not use beyond the expiration date. Once it's opened, consume within 2 weeks according to this article. The homemade version won't last quite as long. Expect a shelf life of 5-7 days according to MSN. It will probably taste best within 3-5 days.