When cinnamon (or other spices) is past its "best by" date, I know that the flavor and potency will be less strong. However, is it still safe to use it on food?
(This came up because a co-worker asked me today whether he would be safe eating cinnamon that expired five years ago on a sweet potato at lunch. Why he has a very old container of cinnamon -- indeed, any cinnamon -- in his desk drawer, I didn't get around to asking.)