Can mold spread to unopened butter? My daughter left a crockpot of food in the refrigerator for over a month. Mold was crazy bad in the crockpot. 3 packages of unopened butter were in the refrigerator also. Should they be thrown out?
Butter is mainly fat - no nitrogen. (It is about 0.8% protein by weight.)  So it is not a very nutritive environment. But its principle protection is that it is “dry”. Although it is about 16% water, that water is emulsified and therefore protected from contamination.  The original wax paper wrapping, and the surrounding container, as well as the temperature of the fridge, would make it very difficult for microbial contamination or growth to occur.