We picked up an inexpensive molcajete at Chicago's Maxwell Street Market last year, but it's left bits of rock in our food every time we tried to use it. Not tasty. We were ready to replace it when we learned it has to be properly seasoned – with rice! Molcajete's are traditionally made of volcanic rock, but inexpensive versions are often made of concrete and other soft stones, making them softer and more sandy. Whatever the material, it needs to be seasoned by grinding uncooked rice into a powder, and repeated until the powder is white, instead of gray.
Gourmet Sleuth recommends following that process by adding actual seasonings to the mix – 4 cloves of peeled garlic, 1 teaspoon of cumin and 1 teaspoon of salt. Grind that mixture with into the molcajete and then discard and rinse.
They also warn that some cheap versions may never be rid of sand completely, and those should be used only for decoration or serving. We have a feeling ours may be in that category, but we're going to give this seasoning trick a try.
Related: Word of Mouth: Molcajete