Thanks for the question. When bokashi bran is stored correctly (at room temperature, out of direct sunlight and in an airtight container), then the bokashi bran remains effective for up to 2 years. Some microbes may survive longer, but the effectiveness of the bokashi bran will decline over time.
If you are unsure how old your bokashi bran is, the best way is to test it. Start a bokashi bucket with food waste and the bokashi bran. You will soon know if the bokashi bran is expired as the food waste will start to rot, rather than ferment. Putrid smells and blue/green mold are sure signs that the bokashi bran is past its past.
Happy composting 🙂