Pickle is stored in ceramic pots but not in earthern pots.why?

The trick to making pickles is to keep them from molding while the pickling process does its thing. The food is submerged in liquid and a weight is put on top to keep it submerged. if the food is finely divided, such as sauerkraut, the weight must be chosen to nearly but not completely cover the surface, so bits of food can't slip by the side and float out where it gets to the air.

Ceramic has a layer of glass. Earthenware does not. Earthenware can harbor mold or even flavors from a previous batch of food.