I've never had that problem. I store kava in the fridge, and it takes several days before it gets a "funk". You may want to try bottled water, or boiling your tap water... or make sure your kava powders haven't been exposed to a lot of moisture/ contamination. Also remember to wash your hands if you're kneading. My kava can easily sit three days and taste just fine, though it does certainly get thicker. Also make sure it's covered. 99% of funky smells in anything in your fridge will be caused by bacteria that is in the air, the food, or the fridge. Put a stop to the contamination, and it'll last longer. You have to figure out where the contamination is coming from, is all, which might take some experimentation. Although an easier fix might be adding a good amount of lemon. The acidity will retard the growth of most bacteria.