B.S. Remover and damage to my keg

[mbcobc]

I bought a used corny keg that had been previously used for beer, and had some pretty stubborn beer stone on the bottom and a bit in the dip tube. I did a couple overnight PBW soaks with the hottest water that the tap would put out, an overnight vinegar soak, an overnight Star San soak, and a lot of elbow grease with a Scotch-Brite No-Scratch scour pad. It was almost gone, but I also wanted peace of mind that I actually got it all, so I bought some Five-Star B.S. Remover and soaked the bottom for ten minutes to no avail. Following the instructions I tried an undiluted ten minute soak and it worked! Continuing to follow the instructions, I drained the keg, did NOT rinse, and left to air dry. Three days later (today), I planned on finishing up with a final PBW soak and Star San soak to finish it off, but the inside went from pristine to this:

There is no scrubbing this off, so I'm looking for some solutions and answers. What happened here? Is this keg done? Can it be restored? How?

 

[RPh_Guy]

Bar Keepers Friend to the rescue!

You should also consider passivation (with citric or nitric acid).

 

[mbcobc]

To the rescue?

That is pretty relieving, and I'm feeling a little more hopeful now. I'll give that a try tomorrow evening. Thanks for the tip!

 

[IslandLizard]

Bar Keepers Friend to the rescue!

You should also consider passivation (with citric or nitric acid).

Doesn't BKF passivate stainless? It contains oxalic acid. After scrubbing just leave it on for a few hours. It will dry, then wash off.

 

[ba-brewer]

My BKF says rub in then rinse thoroughly within a minute then wipe dry.

 

[Robert65]

Yeah, but you can use it in ways the OEM never intended. It is 7.5-9.5% oxalic acid according to the SDS.

 

[day_trippr]

I don't know how deep BKF's passivation power is vs alternatives but it's good enough to keep my factory-passivated kettles bright inside...

Cheers!

 

[SEndorf]

Help me out here...
I thought heat was needed to create beerstone. A problem particularly for boil kettles.
I've never heard of it in a keg. Is this not accurate?

 

[Robert65]

Primarily occurs in fermentation vessels, kegs, and draught systems. Product of evolution and precipitation of calcium oxalate not sufficiently eliminated in the boil. Evolution and precipitation can continue in package, the principal cause of gushing not attributable to infection. Sufficient calcium levels in the boil (>50 ppm) will precipitate oxalate upstream, preventing all of these problems.

 

[RPh_Guy]

Doesn't BKF passivate stainless? It contains oxalic acid.

Can you find any scientific source to support that idea? Seems like a myth.

I only see scientific and professional sources (e.g. NASA) indicate that citric or nitric acids passivate.

 

[mbcobc]

I followed the BKF instructions, and limited the contact time to 1 minute per scrubbing session before rinsing. I scrubbed the floor 4 times, the walls once, and the ceiling and post centers once as well. Overall it did a pretty good job, but there are still these little white flecks all over. They show up on the floor as dark flecks, but the other picture shows them a little more clearly.

I could try TSP to see if that makes any difference. Beersmith recommends 5-10 minute contact time with BKF, I could try that as well. Any idea what these flecks are?

Still looking to figure out the brown resin looking stuff that was coating the inside of the keg after the B.S. Remover. I think a lesson that I couldn't find anywhere before applying B.S. Remover was this:

"For Stubborn Scale and Stone
Follow the directions above, but do not dilute*. Apply full strength to area
*Except before you air dry. Do not allow full strength solution to air dry"

 

[mbcobc]

Here's a thread with the poster having a similar issue with one of their brite tanks

https://discussions.probrewer.com/showthread.php?30355-Rust-streaks-in-tanks-following-passivation

In their case, the white streaks are in the material and they cannot get them off, but it hasn't caused them any trouble with the 3 or 4 batches of beer since using the tank. Wisdom on that thread says that you never let any acid air dry, and that the instructions on B.S. Remover are wrong.

I'm concerned that they are pits and that I won't be able to sanitize properly. I guess we'll see.

 

[beersk]

This same thing happened to me. I thought I ruined my keg! What I ended up doing was rubbing on pure Star San to the inside of the keg and letting it sit for a day or 2. I had to end up doing this a couple times before the weird spots all went away. Man, I was frustrated when that happened. I'm kind of leery to use the BS remover now.

And, I think I tried BKF as the suggestion of someone or something I read and it hadn't worked. Thus, the straight Star San.

 

[Bobby_M]

Can you find any scientific source to support that idea? Seems like a myth.

I only see scientific and professional sources (e.g. NASA) indicate that citric or nitric acids passivate.

Citric and Nitric just happen to be the common acids used. All you need for passivation to work is an acid that attacks iron. Dissolve the iron off the surface, rinse the acid away to expose a consistent layer of chromium, allow to dry and wait a day or so for the chromium to oxidize into chromium oxide. You can also achieve the same end mechanically by sanding or wirebrushing the surface.

Professional source? I have been soldering and welding stainless professionally and passivate the worked areas mostly mechanically and sometimes using 90% oxolic when I can't mechanically do it. I never have reports of rusting. When customers sometimes get minor rusting in the factory weld locations of kettles and fermenters (even the high end brands occasionally), I advise a bar keeper's friend treatment and I have never heard of a recurrence.

I'm not NASA but it's empirical enough for me.

 

[RPh_Guy]

I agree rust isn't a concern.

We are passivating to prevent iron from interacting with our wort. Iron catalyzes oxidation reactions (Fenton reactions).

Nitric and citric acid selectively remove iron, unlike other acids. This obviously can't be done mechanically.

Edit: sorry I thought this was a different thread.