This is because the porous surface can release particles of stone and grit into your food upon first use.
Care for granite mortar and pestle.
To clean stone mortar and pestles made from marble granite or lava stone use warm water and rice.
Clean ceramic glass and metal alloy brass iron mortar and.
Grind a handful of uncooked rice in the mortar and pestle by moving the pestle in rotating pressured motions alternated with up and down pounding.
Check the ground rice for dirt or granite particles.
Seasoning preps the surface and removes any of these particles.
Read any instructions that were included with your mortar and pestle and follow any tips for cleaning and care.
If you have an unseasoned mortar and pestle or one made out of granite stone then you need to season it before using.