Cumin -- from a plant that is indigenous to the Mediterranean -- brings the musky edge to curries and deepens the flavor of chili. Its seeds are sometimes used whole, but more commonly they are ground into powder. Whole cumin provides intense bursts of flavor when you bite into the individual seeds. Ground cumin integrates more fully with other ingredients and seasonings. As a powder, it comes in smaller, more numerous granules that can fade into the background of a dish more easily than the larger seeds.
Read the Recipe
Most well-written recipes call for ground cumin or whole cumin seeds. If a recipe does not specify, it's usually best to use the ground version. When in doubt, consider the role that cumin plays in the recipe. If it is a pilaf or a curry that showcases whole or toasted spices, use whole seeds. If cumin is added to a soup or stew along with other spices, use the powder, which blends in more easily.
Toasting Add Flavor
Recipes such as curries, which showcase spices, often start with the step of toasting whole spices on low heat in a dry pan to bring out their flavors. This process requires whole rather than ground spices, which are prone to sticking to the pan and burning. The instructions may also call for grinding the toasted spices in a spice grinder or coffee grinder, to enhance flavors and make it easier to integrate the seasoning.
Whole cumin seeds have a shelf life of at least a year if you store them in an airtight jar or container. Ground cumin loses its strong flavor and aroma after a few months, even if you store it well. Grinding your own cumin from whole seeds allows you to store the whole spice in your cupboard and have it on hand when you need it, while still enjoying the flavor and texture of the ground version.
Grind Your Own
Grind your own cumin using a mortar and pestle, or a spice grinder or coffee grinder. Your regular coffee grinder will work in a pinch, but make sure to clean it well afterward so your coffee doesn't taste like cumin. Consider investing in a separate, dedicated grinder for spices if you plan to grind cumin and other spices regularly.