I use a swamp cooler to keep my fermentation cool: a bucket full of water where my carboy or bucket goes in, and a t-shirt draped over the carboy/bucket with a fan pointed at it.

One room has two carboys in it and no sunlight hits them, so I use a white t-shirt over those and use bleach in the water of the swamp cooler.

However I recently just set up two carboys in another room where light now hits them, so I use a black t-shirt over those. At the time I set them up 4 and 5 days ago, I used some star san solution left over in the swamp cooler. But now that it has been over 3 days, the star san isn't sanitizing.

I can't use bleach in the swamp coolers with the black t-shirts as it will bleach them white and allow sunlight penetration.

Liquor is too expensive. Star San likewise.

What is an alternative that fits my needs?

Thank you!

  • 1
    Why do you think the StarSan is no longer sanitizing? The way to know is to check pH - it's working still if pH < 3.5
    – mdma
    Jun 15, 2013 at 7:24
  • Also a black T-shirt most likely isn't enough to block the light from the sun. As long as it isn't direct sunlight you are probably okay, but if the carboys get direct sunlight and you are worried about the light use something like aluminum foil. That would be a much better way to block the sunlight. Also the t-shirts will eventually get moldy and decay if they are cotton. Aluminum foil will not. But then again it won't wick up the water either so you could do both. Jun 15, 2013 at 15:45
  • To piggy-back of mdma's response, StarSan will last you months if properly diluted in water.
    – Scott
    Jun 17, 2013 at 13:03
  • 3
    A black t-shirt in sunlight? You’re working against yourself, as that will retain heat. As Plaisier mentioned, just duct tape some aluminum foil over the primary then use your regular white t-shirt over that to keep it cool. (Back in the day I had to use about a cup of bleach in the bathtub or beer gnats would take over the house, and crusties would grow on the t-shirts. It had nothing to do with keeping the beer sanitized, it had to do with keeping the room sanitary.)
    – ipso
    Jun 18, 2013 at 17:01
  • @MDMDA I got that information from John Palmer's online book (first edition): howtobrew.com/section1/chapter2-2-3.html Jun 20, 2013 at 23:01

4 Answers 4


I would suggest the iodine-based sanitizer knows as "Iodophor" if you really feel the need to sanitize the water:


This stuff is an iodine-based sanitizer, fairly common in homebrewing (but probably not as common as Star San). I started out my homebrewing career with it, and still have some left. A big bottle goes a long way.

In proper dilutions, the treated water is barely colored with a very, very pale amber tint. There's no chance you'd see such a tint on any dark shirts that you are using to wick up the water, although you MIGHT see pure white t-shirts get a bit "dingy" if you used them.

Like Star San, this stuff does not maintain sanitization for multiple days, but sinec a 32oz bottle cost around $15 and you'd be using a cap full a day at most, we're talking pennies per day probably. Be sure to pick up some test strips as well, since they will tell you the exact strength of the sanitizing solution:


Actually, most of the time when you order Iodaphor, the home brew shops will throw in some test strips for free, so you might not even have to purchase those.

Final unrelated note: you really, really need to get that carboy out of direct sunlight. Don't rely on a t-shirt to block the UV rays.

  • I'd agree with most everything here, but: StarSan will absolutely maintain sanitizing capability for months at a time if made with distilled water and kept free of contaminants.
    – jsled
    Jun 18, 2013 at 3:55
  • Yeah, too bad you can't really keep it free of contaminants in a swamp cooler. Does oxygen exposure start neutralizing StarSan too? I can't recall off the top of my head.
    – GHP
    Jun 18, 2013 at 12:04
  • @jsled Plesae check my comment to MDMA under the OP question, regarding John Palmer's opinion on Star San. Jun 20, 2013 at 23:06
  • @Graham thanks for the suggestion I will try it out. Jun 20, 2013 at 23:07

Just use water. The evaporating liquid does not need to be a sanitizer, per se.

  • +1, your carboy/pail isn't permeable to water or any similar liquid (assuming there's no cracks or holes, or completely submerged under water, in which case no amount of sanitizer in the water will save your beer), so there's no reason to be concerned.
    – Scott
    Jun 17, 2013 at 14:30
  • Good sanitization habits are important, but using anything besides water in a swamp cooler is going overboard.
    – paul
    Jun 17, 2013 at 19:58
  • Although I'm not clear on the OP's full intent, I have some sympathy. The one time that I tried a swamp cooler, the wet t-shirt grew mildew on the underside. Don't know what that says about my garage, but definitely a disgusting consideration for swamp coolers. Jun 17, 2013 at 22:42

I'd personally use bleach for this--get some white fabric instead. One teaspoon per gallon is a good minimal concentration. Maybe try 2 tsp. Whatever you use, it will end up concentrating, as evaporation (like distillation) will leave behind everything but the water. Wash your fabric occasionally to remove this concentration (phosphates and organic salts in the star san case, iodine in the iodophor case).

I agree you shouldn't need to sanitize this per se, as your fermenter should be sealed w/ air lock. However, a little chlorine is a cheap way to avoid mold build up on things you won't be consuming.

  • I'm with ajfabbri - bleach will fight mildew and mould, things you don't need near your fermenter lids and seals. Jun 19, 2013 at 6:38

I tried using a swamp cooler, but found picnic ice packs to be much more effective. After the initial investment, they are free. I just change them out a couple of times a day for the first three to four days.

  • Hey Blue Murphy could you post a link to what you are describing? And do you still use a tub full of water to place your carboy in as you do with the swamp cooler? Jun 20, 2013 at 23:08
  • I am talking about these google.com/shopping/product/… I have a rubbermaid tub big enough to put 2 ale pails in and then fill it up with about 10 gallons of water. I then throw in 4-5 of these and change them out at least twice a day. I also bought an aquarium pump so that there wouldn't be any temperature stratification. Even without the ice, it stays 4-5 degrees cooler than room temp Jun 21, 2013 at 0:36

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