A resposta é diferente para cada tempero e moagem. A maioria das fontes que vi sugerem que 6 meses é o longo caso de 'especiarias frescas', mas todas sugerem moagem em pequenas quantidades, para que você não precise que elas durem tanto tempo.
A seguir, algumas informações de " Spice Mogul ", algumas básicas "faça e não faça"
Faz
* Buy spices whole, versus ground, whenever possible.
* Buy in quantities that you will likely use up in 6 months time.
* Mark the date you buy your spices and dried herbs. If there are no dates on the package, take a marker and date each container when opened.
* Grind spices just before using. Grinding releases the volatile compounds that give a spice its flavor and aroma. The longer the spice sits around (either whole or ground), the more the compounds disappear and the flavors lessen.
Não
* Store spices and herbs on the counter or close to the stove. Remember that just like with oils, heat, light, and moisture are enemies of a spices flavor and shelf life. Cool, dry and dark should be your watch words.
* Forget to check for freshness.
* Use pre-ground spices if you can avoid it. If you must, test for flavor by rolling a small amount between your fingers and taking a whiff. If it releases a distinct aroma, you’re ok. If you have to strain to smell it, pitch it and buy fresh. There is no sense in ruining a dish full of other ingredients because your spices are not up to their full strength.
O Spice Mogul também tem uma boa coleção de conselhos específicos que você pode querer revisar.