I do mix with a touch of flour, which I have pre baked at 200 degrees to make it extremely dry. But before that I will put the pollen in a small jar without a lid inside a much larger jar nestled in some desiccant. So the desiccant isn't actually touching the pollen. Let me know if that does not make sense. Rice might work but probably not very well, I think if you really bake it dry at 200°. Much better are the desiccant balls you can buy online. They change color when absorbing humidity + can be reused by baking in the oven. Those little pouches that come in seaweed packages and the like are not good enough. After it sits in the small jar inside the larger sealed jar resting on desiccant for several days. I will then add the dried flour, put into smaller containers so I have several and don't have to open one container every time, + then label it, date it, seal it up and freeze it. When you pull it out of the freezer, just like when you're pulling seeds out of the freezer, before you open the jar, you will want to let it come to room temperature. That will help reduce any introduction of moisture that might occur from condensation.