Refrigerate unopened tempeh and use it before the 'best by' date. Once opened, use or freeze tempeh within 3 to 5 days of opening. Unopened tempeh can be frozen in the original packaging for up to one year if the product is put in the freezer before the 'best by' date. Quality over time will be diminished, especially if they are frozen close to the 'best by' date. If the tempeh has already been opened, then you can freeze it by wrapping it tightly in a double layer of plastic wrap, or in a freezer-safe airtight container.