It's generally not recommended to share spice grinders across different masalas, especially if you want to maintain the purity and distinct flavor profiles of each blend. Residual flavors from previous masalas can contaminate subsequent batches.
When you grind spices, tiny particles and oils get lodged in the grinder's crevices. These remnants can significantly impact the taste of your next masala. For example, if you grind a garam masala with cloves and cinnamon, those strong flavors can linger and alter the taste of a milder masala you grind afterward, like a coriander-cumin blend. This is particularly noticeable with potent spices like turmeric, chili peppers, and fenugreek. While thorough cleaning can help, it's difficult to remove all traces of previous spices, especially from grinders with intricate designs. Dedicated grinders, or at least dedicated grinder attachments, ensure that each masala retains its intended flavor profile. Using separate grinders also prevents cross-contamination, which is important if you have allergies or sensitivities to certain spices.
If you must use the same grinder for different masalas, grind the milder spices first and the stronger spices last. This minimizes the impact of flavor transfer. Also, try grinding a small amount of white rice after grinding spices to help absorb residual oils and flavors before cleaning.