Eggshell is covered by a protective protein membrane, the eggshell membrane, which stops the invasion of bacteria and other micro-organisms and hence, extends the storage period of eggs. Eggshell should only be rinsed before consumption; otherwise, bacteria may deteriorate the egg by penetrating through pores on the surface of the eggshell. Some eggshells are dirty, so these eggs may be stored in food bags or wrapped with cling films before putting in a refrigerator to avoid contamination of other food.