Reason for difference between the “taste” of vegetables by using ground spices and powdered spices

Question

I used to use powdered spices for all my vegetables. Lately I have started grinding the spice seeds myself to use in the vegetables.
I have noticed a remarkable "taste" difference.

I wish to know the reasons.
P.S. I am NOT referring to the smell, but to the taste.

Answer

This difference in taste is due to the oils and aromatic compounds which give many spices their flavour having broken down or escaped over time.

Very fresh powdered spices wouldn't have this issue. Also if you ground the spices yourself and then left them for a few week/months you would find much of the taste has gone from the powder.

Some spices stay fresh for a long time once ground, others are well worth (as you are finding) doing your self.

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