Black spots on stainless aeration stone?

Last time I used the stone, I washed it off with water then put it in a plastic bag...
Two weeks later, I notice there are some black spots on the stone. I thought it might
be mold, so I boiled it for 20 minutes. But the spots are still there.

Should I scrape or use abrasives to clean it off ? Any problems with this ?

You may want to contact the vendor for some help so you don't ruin it.

It's possible it's just some oxidation and discoloring on the stone. Give it a good soak in some Star San. The acidic nature of it should clean the stone a bit and help kill anything that could be in there. But really more for the cleaning side things.

most vendors suggest treating stones extremely carfully, not handling it to avoid getting fingerprint oils on them, for instance. the holes are extremely easy to clog. sanding or scraping would definately make that section not function properly. they are essentially foamed metal, and if you want those 1/2 micron holes to remain the same size, you really shouldnt touch them with anything.

a particle of dust, for instance, is 2-50 microns. yeast cells are around 20-50 microns. its very easy to clog these things. after use, you should immediately clean the stone in hot starsan or hydrogen peroxide, then dry it by pumping filtered air, CO2 or O2 thru it, and store it in a very clean sealed bag.

Thanks for the responses...
No Star-san - any alternatives? [ I use idophor]
I'll check the pores to ensure they are clear (w/ huge O2 tank.)
I've never handled it with my hands and the bag was new, so it should be clean,
especially after the boil...

I'll ask the vendor. Thanks.

Get a magnifying and give it an upclose look. It's probably just discoloring of the metal. Maybe some hot PBW. Even if it was something living, it's dead now that you boiled it. Unless you are propegating those algae that live next to 400F thermal vents. I wouldn't sweat it too much as long as it still works.

Disolve some Bar Keepers Friend in a beaker of hot water. Soak the stone in the water. The acid in the BKF should clean up the stone.

skipper1953 said:

Disolve some Bar Keepers Friend in a beaker of hot water. Soak the stone in the water. The acid in the BKF should clean up the stone.

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I didn't even think of using BKF on that. Good call.

You know, I had the exact same thing happen last night. During the boil I pulled out my Williams aeration stone (used on 4 batches now), and it had a bunch of mold on it. After the last brew I had soaked it starsan, then put it in a plastic bag, figuring it would be fine. Not so, apparently.

I boiled it for about 20 minutes, and got most of the mold off, but the stone still has black spots on it. Seemed to work fine for aerating, and I figure a 20 min boil has got to kill any nasties, but I'm a little worried, too. Maybe I'll give that Bar Keepers Friend idea a shot.

Any update on the success of getting rid of the spots. I have a .2 micron stone that I purchased from morebeer in 2009. It's never been used and I've kept it in a sealed ziplock bag since purchase.

I was planning to use the stone this week. So I boiled it for 20 minutes prior to testing with 02.

After the boil, you guessed it -- black spots.

I have it soaking in alcohol. And will try the concentrated Star San before moving to BKF.

That is, unless someone's found something that works.

Cheers!

So I guess we can safely assume this is just oxidation on the stone, and not some bacterial infection. I would say not to worry about the look of it

Why would stainless steel "oxidize"?

I've been using the same .5 micron SS air stone for years and I've never seen anything that changed its color from bright stainless. Then again, I never store it in a sealed environment...

Cheers!

day_trippr said:

Why would stainless steel "oxidize"?

I've been using the same .5 micron SS air stone for years and I've never seen anything that changed its color from bright stainless. Then again, I never store it in a sealed environment...

Cheers!

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It would oxidize because it's not true solid stainless. It is sintered. It would not be truly passified. Look at the outside of keg that has set around. I bet it's discolored a bit. You are also pumping O2 or air through it which would lend itself to creating oxidation rather quickly.

After soaking my stone in alcohol for 4 hours with little to no effect, I moved to a soak in very concentrated Star San.

After this eight hour bath the stains did seem fainter, but still there.

I rinsed the stone and set it out to dry.

When I arrived home from work, they were gone.

I'll let you know if they return following next use.

mobilecabinworks said:

It would oxidize because it's not true solid stainless. It is sintered. It would not be truly passified. Look at the outside of keg that has set around. I bet it's discolored a bit. You are also pumping O2 or air through it which would lend itself to creating oxidation rather quickly.

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I've been running pure oxygen through that stone, four to five minutes at a crack, at least twice a month for nearly three years. Not even a hint of coloration, never mind black spots.

I don't think your theory holds water. Or gas. Or pretty much anything. Something else is going on - that's my theory...

Cheers!

day_trippr said:

I've been running pure oxygen through that stone, four to five minutes at a crack, at least twice a month for nearly three years. Not even a hint of coloration, never mind black spots.

I don't think your theory holds water. Or gas. Or pretty much anything. Something else is going on - that's my theory...

Cheers!

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Not every sintered air stone is the same. Could be an inferior material that was used. Could be from China. Who knows. But if you have boiled it for 15 minutes, anything that was living on it before, is dead now. Vanity is vain. RDWHAHB.

day_trippr said:

Why would stainless steel "oxidize"?

I've been using the same .5 micron SS air stone for years and I've never seen anything that changed its color from bright stainless. Then again, I never store it in a sealed environment...

Cheers!

Click to expand...

Stainless will rouge, just google stainless rouge, it is commonoly acknowledge in industry. I see it all the time on stainless. A stainless surface that is not properly passivated or has not been passivated is susceptable to this. Even a properly passivated surface will begin to rouge given enough time.

An acid soak may help depending on the severity but if the acid is harsh enough to get rid of the rouge it will be changing the size of your pores slightly as well.

Way late to this post, but I was just mid-fly sparge and pulling out equipment for the next steps. I pulled out my aeration stone to boil, which I recently purchased from Northern Brewer. I haven't been able to brew for about a month due to a newborn, so it's had plenty of time to sit. This thing has black all over it, and it's like ink..it's really bizarre. It doesn't look like mold, or at least no mold I've ever seen. Boiling now, will give it a 20 minute boil, replace water, boil again for 15 minutes and then soak in star san until it's time to use it...really crazy stuff!! Oddly, the last thing I did with it was soak it in star san after using it.