That's something I hadn't really thought about -- I always thought if it still smelled good then I was in the clear! I had to research though for my own knowledge and found this:
If spices and herbs are kept as we have discussed the shelf life will be as follows:
Just because a spice or seasoning blends is outside the date range listed above doesn't mean that the spice needs to be tossed in the trash. To determine if a spice or seasoning is still good you have to remember "appearance" and "aroma". A spice that is no longer acceptable will have lost much of it's vibrant color and will instead appear dull and faded. The bigger key though is smell. To determine whether or not a ground spice is still good gently shake the container with the cap on. Remove the cap and smell the spice to see if the potent aroma of the spice is still present. If it is then your spice is still in good shape.
- Whole spices and dried herbs, leaves and flowers will keep 1 - 2 years.
- Seeds will keep 2 – 3 years and whole roots (i.e. ginger root or galangal root) will keep 3 years.
- Ground spices and herb leaves keep 1 year.
- Ground roots will keep for 2 years.