Once the bottle is opened or not, Kombucha can be kept in the fridge for about 3 months. However, it really never spoils due to its low pH which prevents harmful microorganisms and foreign pathogens from invasion. The brew will continue to ferment at a slower rate in the fridge than when stored at room temperature and becomes more sour over time which may not taste as delicious as it was before. Despite the ageing beverage, it is still safe to drink.