Yes, roasted cumin seeds should be cooled completely before grinding. Grinding hot seeds can release oils and create a paste-like consistency instead of a fine powder.
Roasting cumin seeds enhances their flavor and aroma, making them a valuable addition to many dishes. However, the heat from roasting can also make the seeds more prone to clumping when ground. When cumin seeds are hot, their natural oils are more easily released. Grinding hot, oily seeds in a spice grinder or mortar and pestle can result in a sticky, uneven paste instead of the desired fine powder. Cooling the seeds allows the oils to solidify slightly, making them easier to grind into a consistent, free-flowing powder. This ensures that the ground cumin has the best flavor and texture for your recipes. To cool the seeds, simply spread them out on a plate or baking sheet after roasting and let them sit at room temperature for about 15-20 minutes, or until they are completely cool to the touch.
If you accidentally grind the cumin seeds while they are still warm and they start to clump, try adding a small amount of rice to the grinder. The rice will help absorb the excess oil and create a drier mixture.