A spice's flavour lives in volatile aromatic compounds — terpenes, aldehydes, essential oils — held inside cell walls until grinding ruptures them. Once broken, those compounds begin to leave. Not slowly: the aromatics in freshly cracked pepper or cardamom dissipate measurably within minutes of exposure to air, and substantially within an hour. Ground spice sitting in a jar is releasing what you bought it for.
This is not a question of freshness in any vague sense. It is chemistry. The cell structure of a dried peppercorn, cumin seed or coriander berry acts as a sealed vessel. Whole, it can store volatile oils for months with manageable loss; powdered, the surface area expands by orders of magnitude and the oils find nothing between them and the air.
The practical consequence is that the same spice — the same harvest, the same origin — produces a categorically different result depending on whether it is ground to order or purchased pre-ground. Black pepper ground ten minutes before use has a brightness and heat that pre-ground pepper cannot replicate. Cardamom pods, split and ground just before they go into a masala chai or a biryani, carry a floral eucalyptus note that the green powder in a tin has lost almost entirely.
Roasting before grinding intensifies this further. Dry heat drives volatile oils briefly outward, primes the aromatics, and simultaneously unlocks new compounds through the Maillard reaction. The window between roasted and ground, and ground and used, is where the flavour sits.
Indian cooking at the level of the household or the professional kitchen has always assumed grinding fresh. The stone sil-batta (grinding stone and roller) and its regional equivalents are tools for this — not ritual, but function. Spice merchants selling into export markets have long known that whole spices travel and store; ground spice is already partway spent before it leaves the warehouse.
The argument for buying whole is, in the end, simple: you are buying the sealed vessel, not the opened one.
This is not a question of freshness in any vague sense.