Seeds do carry on their basic life processes even while in the dormant stage, just at a very slow rate. The point of keeping the seed stored properly is to prevent the metabolic activity from accelerating to the point of germination. To make this happen you need to keep your seeds away from moisture and heat, and hungry critters who may want to eat them.
Storage temperature, relative humidity and seed moisture are the important factors in determining how long seed can be stored without loss of germination.
Appropriate Storage Containers
Package the seed in moisture-proof containers and store it in a refrigerator or freezer. A moisture-proof container is one that stores seed safely while submerged in water. Use sealed cans or jars, rather than plastic bags. In general, longer seed storage life is obtained when seeds are kept dry and at low temperatures. Storage temperatures between 35°F and 50°F are satisfactory when the moisture content of the seed is low. Don’t leave your seeds hanging around in the open air, especially if you live in a humid climate, as they will absorb moisture from the air.
Get your jars ready for the freezer. Date each jar so that you know when you stored the seeds. Specify which seeds came from your own garden if you want to keep them separate.
How long can the seeds can be stored and still be viable?
Conditions Essential to Good Seed StorageConditions essential to good seed storage are just the opposite of those required for good germination. Good germination occurs when water and oxygen are present at a favorable temperature. Good seed storage results when:
Drying Your Own Seeds Before Storage
If you are collecting and saving your own seeds from vegetables you grew, most seeds, in most climates, will dry adequately for home storage when spread out on a paper towel or newspaper in a well ventilated in a shady spot or inside for a week. Depending on the type of seed, you may need to change the paper a few times. Avoid the temptation to rush the drying process by adding heat. This may cause the seeds to crack or shrink and make it so the seed coat is impenetrable. Drying the seed at too high a temperature (anything above 100 degrees) will greatly reduce the seed viability. Also, if you accidentally expose your seed to moisture after you have dried them, you greatly reduce the viability of your seed by trying to dry them again.
Beans and peas are particularly subject to over drying and therefore should not be dried as completely as other seed. If they have been over-dried, they germinate better if exposed to a humid atmosphere for two weeks before planting.
Remove your seeds from the freezer when you're ready to plant them. Set them aside until they come to room temperature again before using your seeds to reduce condensation in the jar.
References:Seed to Seed by Suzanne Ashworth