As the growing season for your beans draws to a close, select some plants to stop harvesting. Allow the beans on these plants to mature and dry out.
When the pods are completely dry (most varieties will appear tannish or brownish at this stage) and the seeds rattle inside the pod when shaken, pick the bean pods.
Once you've collected all your pods, you can remove the seeds. A dry pod will split open when squeezed gently along the seam. Collect all the seeds and discard the empty pods.
Lay the seeds out on a paper or towel or on several layers of newspaper and allow them to air out and dry for several days. It is important that the seeds are dry and clean when you store them. Dirty or damp seeds run the risk of rotting or growing mold. When the seeds are dry, sort through the seeds discarding any shriveled, broken, or discolored seeds.
Pour the seeds into a clean dry container. Make sure the container is moisture proof. Paper and cloth are absorbent and could soak up enough water to cause the seeds to rot or grow mold.
Make sure to label the container with the variety of seeds enclosed and include the month and year that you collected the seeds. Store the seeds in a cool dry location.