If your water kefir has a yeasty aroma you may be over-culturing, which can cause an imbalance. Make sure to reduce the culturing time in warmer temperatures, to keep the grains well-fed and in balance.

With grains that have been in use for a while but have begun to smell yeasty, you might add  ⅛ of a slice of a piece of lemon to 2-3 batches, to increase acidity and reduce the yeast.