Spices should be cooled completely before grinding. Grinding hot spices can create a paste or clump due to the release of oils and moisture.
When spices are heated, their volatile oils are released. These oils are what give spices their distinct aroma and flavor. Grinding spices while they are still hot from toasting or roasting causes these oils to be released more readily. This excess oil can lead to the spices clumping together, forming a paste-like consistency, or sticking to your grinder. This makes it difficult to achieve a fine, even grind. Allowing the spices to cool completely ensures that the oils are reabsorbed, resulting in a drier, more brittle texture that is easier to grind into a fine powder. Cooling also helps to preserve the volatile oils, preventing them from evaporating and losing their potency. The ideal method is to toast or roast your spices, let them cool to room temperature, and then grind them immediately before use for the freshest and most flavorful result.
To speed up the cooling process, spread the toasted spices in a single layer on a cool baking sheet. This allows for better air circulation and faster cooling, preventing the spices from retaining heat and releasing excess oils.