Can I add lemon to my kefir? You shouldn't add lemon, or generally any citrus, to your kefir.While the culture is acid resistant, the pH can become too high and will kill off the good bacteria you need to form the kefir. Related articles How much kefir should you have per day? How long can kefir be stored in the fridge? How do I make kefir fizzy? When do I remove the stainless steel mixing ball from my kefir? How to Guide - Kefir