How old is too old, if you're a spice?
I've heard so many conflicting things about how long spices last. Recently received a wonderful box of Penzey spices for Xmas, but am not sure if/when I should purge the contents of my vast spice cabinet. Some are undoubtedly over a year old. Thoughts?
How about letting your sense of smell and taste tell you? Compare the new stock with the old. The problem with old spices is that they go stale, not that they go bad. Toss the old if you have something better to replace it with, or if you need the space.
There's the old standard - whole spices last longer than ground.
I don't think purging the old stuff is all important. If it is old, it means you don't use it much, and really don't care if it is fresh or not. If you use it regularly, you have good turn over, and you know what is fresh and what is not.
I wouldn't buy a fresh supply of coriander seeds (mine are unknown years old) just because I might use them once or twice in the next year. On the other hand, I use cumin enough that I buy both whole and ground at least once a year - not because it is old, but because I run out.
Instead of throwing the old spices out you can double the amount in the recipe, or you can toast it before adding to the other ingredients.
I buy as many of my herbs and spices as possible whole and then grind them fresh every few months. I grew many herbs so they don't get a chance to get stale before they are used.
30 if you're posh spice? hahahoho.
if you're a professional chef or otherwise very picky about your ingredients (i'm neither), the rule of thumb for most ground spices is about a year, as you hint. realistically, some of my spices kick around for quite a while longer than that. cinnamon, i've noticed, does not lose its potency for a very long time... years (i think i might even prefer the taste of old cinammon). bay leaves and dried herbs, on the other hand, seem to lose potency far more quickly.
as kelli noted, if the spice is less potent, just use more of it. i almost never measure spices, anyway; i add to taste.