The slime in ice machines is biofilm buildup that contains bacteria and microorganisms. Because the moist conditions found inside an ice machine create the perfect environment for bacteria to thrive, it's important to unplug the freezer and clean it out with bleach spray occasionally to avoid getting sick.
The slimy buildup occurs when an ice machine is not properly sanitized on a regular basis. Warm temperatures and droplets of water are a breeding ground for the slime. It is not uncommon for health inspectors to find mold inside an ice machine. The slime can look pink in color or, if left unsanitized, may turn red or even green.