Michigan State University Extension
Preserving Food Safely - 01600638
Since commercially ground spices lose their flavor and aroma quickly-within six months- many people like to grind their own. As long as spices are whole, you can safely keep them tightly capped in a kitchen cupboard. Spices release their oils by cracking or grinding them, you multiply their surface area at least eightfold and expose them to oxygen. Then the spices belong in the freezer. (That's why ground coffee belongs in the freezer, too).
A coffee mill can be used for spice grinding. If you blend your own curry seasonings from whole spices, be sure to keep the leftover mixture and the partially used spices in the freezer.
Green peppercorns are highly perishable immature peppercorns. If they are purchased packed in brine, you should expect green peppercorns to spoil. Either freeze them on a cookie sheet, collect them in a jar and keep them in the freezer, or add them to butter and freeze them.
One category of spices belong in the refrigerator or the freezer for reasons of safety, as well as for flavor retention. Red spices, including red pepper, chili powder, all the paprikas and cayenne pepper contain insect eggs in their tissues, even after they've been ground up. When the temperature and the humidity are high, worms can grow.