As long as your opened kombucha was stored in the fridge, it is safe to consume kombucha between 5-7 days after opening. Remember that store-bought kombucha generally stays at best quality for up to one week after opening in the refrigerator. Homemade kombucha lasts even longer, up to 3 months, but your kombucha kit will give you a definitive amount of time for which you can keep your kombucha in the refrigerator.