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For the last 2 batches of beer I've used a swamp cooler to cool off the plastic bucket fermenter. The cooling worked well, but on both batches, there was a bit of mold growing on the outside and/or under the rim of the bucket where the wet towel was. I added some sanitizer to the water in the last batch, but it didn't seem to help. Adding bleach to the water seems like a bad idea. Would there be any chance of bleach or another mold-killer ruining my bucket and/or beer from the outside? Is there something safe I can add to the water to keep the mold and other nasties at bay?

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For what its worth, if the bucket gets too moldy, retire it from service promptly. I had once get really speckled with black mold from sitting too long in a humid environment, and I just use it to hold sanitizer now. – Graham Dec 2 '11 at 19:21
up vote 5 down vote accepted

I've used bleach before without any problems. I can't imagine it seeping through the bucket into the beer, unless you use 100% bleach instead of water...

The amount of bleach required to sanitize water is something ridiculously low, so if its freaking you out, then just make sure you only use a little at a time.

"Most emergency experts and health officials suggest a mixture of 8 drops of bleach to a gallon of generally clear water for best results." - http://www.csgnetwork.com/h2oemergencypurifycalc.html

I'd suggest adding a few ounces of bleach every 2-3 days, rather than throwing in a quart the 1st day and leaving it, as it doesn't take much bleach to purify the water, but bleach does evaporate out of the water within a day or so.

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+1 sounds good to me. – Poshpaws Dec 1 '11 at 18:55
Bleach doesn't evaporate out, but the chemical oxidation potential once diluted in water decreases pretty quickly. Thats the reason to refresh every day. – brewchez Dec 3 '11 at 0:08

Bleach is a good choice. But how long are you leaving the fermenter in the bucket? Usually after the first few days temp control is much less critical. I remove my fermenter from the bucket of water after a week and don't see any mold.

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+1 this was my thought too – Ryan Shdo Dec 2 '11 at 14:40

I think I would try using several towels and replace and wash them every couple of days.

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The mold is growing on the bucket itself, though, not on the towel. – Jarett Millard Dec 1 '11 at 18:55

There are professional additives that are used in labs to keep mold from growing in water baths and humidity pans inside incubators. Do you know anyone who works in a lab? Can you find a lab supply store in your area (there is almost always one to supply schools and child care facilities with science equipment). I don't know what the chemical is, I'll try to figure it out next time I see a bottle.

Bleach will work to reduce growth in the water, but it will not "combat" the mold that has already grown. You'll need to scrub and sanitize any areas where you can visually see mold, otherwise it will simply grow back in the same area.

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