Gray Foam - Damaged Kettle?

[ChrisS68]

So yesterday I decided to brew a simple extract batch. I use a 4 gallon stainless pot for my boil kettle. Normally I put it over two burners on my stove, but for various reasons I decided to try it with just one.

Took a long time to get to any sort of a boil - like an hour? I had put in about half of the extract and was stirring occasionally. As it slowly approached boil it began to form a foam as one might expect. What struck me as odd is that, at some point, the foam began to change from a normal beige/brown to a sort of gray color. Looking closely it appeared to have some sort of dary gray flakes in it. Very odd. I thought maybe I was just being paranoid so I let it go. The beer eventually came to to a boil and everything else went normally. The later extract addition did not exhibit the same gray color. However, when I cooled the wort and put it in the fermenter, it seemed a lot more cloudy than ususal with a kind of odd color.

After washing the equipment, I noticed that the bottom of the brew pot was discolored from heat (rainbow effect). More concerning was that there are dark gray scratches all over the bottom of the pot where my spoon had scraped while stirring. I use a plastic (nylon?) spoon and hardly gouged the pot. The spoon shows no evidence of melting or other damage. Is it remotely possible that the pot was somehow damaged in the lengthy boil process? It seems totally bizarre, but now I'm wondering what caused the gray foam, and am worried about what might be in my beer.
Thanks!

Chris

 

[DavidHawman]

Did you clean it out thoroughly before using it?

Taste the wort and see if it has a metallic taste to it(at worst you'll get some more iron in your diet), that might help narrow it down.

The rainbow effect I believe is from oxidation so it could be that your pot just re-oxidized and what you scraped off was the newly forming oxide layer.

I doubt that it was heat damage though, the liquid side of the metal wont get much above 212F as long as wort is in the pot.

 

[springer]

The only thing you can do to a SS pot with a nylon spoon is dent it if you hit hard enough. Highly doubt you have any metal in the wort from a long boil I have done 90 minute to 120 minute boils never noticed anything. Most likely you are seeing some mark from the nylon spoon and a good cleaning will remove them.

 

[Cliff897]

High acids can cause a mirroring of 304 stainless
Mineral haze can too

One should think that mineral haze is removable by washing.

Acid damage is another matter altogether.
I would pour some lemon juice in the bottom of your kettle and warm it up just a tad, not boil, then let it sit for an hour and check it. The Citric acid will passivate the steel.

SST will instantaneously self passivate when there is 10.5% chrome in the metal, but certain bases acids can strip it away. If corrosion sets in you have issues to deal with.

Abrasive treatment and machining can expose fresh clean metal. But you can passivate it too. Passivation is the application of the correct acids which attack the iron more than they attack the chrome leaving a precipitate chrome oxide layer that is more robust than what you normally have from the natural process of the metal.

Traditional passivation meant a nitric and hydrofluoric acid bath at very specific temperatures, solution titration, and times.

You can just use citric acid which takes longer but is way far easier and safer.

Read all about it here:
http://www.iftworldwide.com/white_paper/passivation.pdf

If you want to be a real fanatic about citric acid passivation here is the process:
The citric acid should be a 3% to 10% solution (yah, that wide a margin) and it really helps to have something in the solution that will bind specifically to the iron. EDTA is great cheap and harmless. It binds specifically to minerals and iron especially and will hold the liberated iron in solution. That way it can not redeposit on the surface. Hold the tank at about 77C for an hour. If you can't heat it use more time.

 

[ChrisS68]

Thanks everyone for helping to allay my concerns. It was just kinda weird as I've never had this happen before. And a thanks to Cliff897 for all the info on stainless! I'll give the lemon juice a try and see what happens.

Chris

 

[ChrisS68]

well, the lemon juice did the trick - much better than Scotchbrite did. Thank you!
I might give it another shot though. I didn't have much lemon juice on hand and you can see a line on the inside of the kettle where I tried to swirl it around.
Now the only question is, what caused this, and what was that gray foam?
People are already kinda squirmy about trying this batch...

 

[topsecret]

Hey all,

I know I'm a bit late posting to this, but wanted to chime in as this happened to me on Saturday. I just put together a stainless steel HERMS system, and during boil had an extreme amount of grey matter / haze. I was sure it was from it being the first time we'd used the steel, but I ran boiling water through the system right after and got nothing. Of course, it could've just been from that first run, but after doing some research I learned that pulverized grain can release a dust (along with tannins) that give a very metallic look to the beer.

I decided to ferment her out as usual, and besides some massive clumps of that protein within 24 hours of fermentation things started to settle out fine on the bottom.

Not sure if that's helpful, but seems to be what affected my boil.