When the pack of brown sausage was taken out of the freezer, the warm water vapour in the surrounding air came into contact with the colder surface of the clear plastic and caused the water vapour to lost heat and condense into water droplets. The water droplets continues to lose heat to the cold sausages and it turned into ice when the temperature reaches 0 degree Celsius and therefore, there is white solid seen on the surface of the plastic wrapping.