Any of the polysaccarides that you use in the mix are going to be a problem if they are in a humid environment. Al you have to do is keep it in an air tight container. If you want to make the formula even safer from bacteria, then put it in the freezer. I've had my Improve USA in powder form for eight months now and there is no problem with it. I don't keep it in the freezer but I do keep it in an air tight container and in a very cool dry area.