First of all, you need to confirm the shelf life of kefir yogurt. Generally, if the shelf life is within one month, it can be used as a strain for milk fermentation. If the shelf life is several months, it means that it is a long-lasting yogurt. , it has been inactivated, there is no active fermentation bacteria in it, and it will not make yogurt. Kefir yogurt is also made with kefir.