The amount of flavor contributed by a spice or herb depends on the amount of essential oil it contains, not on the total amount or weight of the whole substance.
Spice or herb that are powdered or ground give up their oils readily in the heat of cooking because their huge surface areas allow their essential oils to evaporate quickly.
Thus, finely divided spice or herb should be added near the end, rather than the beginning of cooking, lest all their essential oils evaporate and the kitchen smell better than the food tastes. Whole spice or herb on the other hand, such as peppercorns and bay leaves, give up their essences slowly and are added at the beginning.
Because most essential oils are volatile, spice or herb lose their effectiveness in storage as the oils slowly evaporate. So fresh spice or herb are always more potent than stale ones. Even low levels of heat can slowly drive off the oils, so spice or herb also should be stored in a cool location. Ground spice or herb lose their strength by evaporation much faster than whole ones.
Nutmeg and black pepper, especially, should always be bought whole and ground on the spot when needed. Hot chili peppers, on the other hand, keep their heat even when dried and ground, because capsaicin, the “hot stuff” in them, is not very volatile. That’s why you can’t tell how hot a pepper is by smelling it.
You’d be surprised at how much of most the verve in spice or herb is lost over the period of a year or less, especially if ground. Sniff your spice or herb; if you can recall that they smelled much more potent when new, replace them with fresh samples. It’s a good idea to date the labels when you buy them. And check the vividness of their colors periodically. Green, leafy herbs such as tarragon and rosemary fade with age, as do red spices such as Cayenne pepper, paprika, and chili powder.
Some spice or herb fanatics (sperbivores?) go so far as to keep their spice or herb in the freezer. I don’t see why that shouldn’t work.
