A dry cooler is a mold-free cooler

The fastest way to kill black mold in a cooler is a bleach solution, but the only way to keep it from coming back is to store it dry.

Mix about a tablespoon of bleach per quart of water, wipe down every surface, let it sit for a few minutes, then rinse like crazy. Bleach kills mold on non-porous surfaces reliably. If the cooler smells even after that, a baking soda paste scrub will knock out the lingering mustiness. Just don’t mix bleach with vinegar or anything acidic — that makes chlorine gas, which is not how you want to spend your afternoon.

The mold will absolutely come back if you close the lid on a wet cooler. That’s the whole game. After cleaning, dry it completely — wipe it, then leave it open in the sun for a few hours. Store it with the lid slightly cracked, not latched shut. Toss in a few crumpled paper towels or a silica pack if you live somewhere humid.

People blame “dirty coolers” but it’s really “damp coolers.” Kill the mold once, then focus on keeping the inside dry and aired out. That’s the fix.