Stainless Passivation

So, I got a Stainless Brew Bucket today, made with 304 stainless steel. The instructions recommend that, after an initial cleaning with TSP, the steel be passivated. The thrifty part of me (Yeah, I know, I did buy a stainless/more expensive fermenter, but it's easier to clean/etc and will last a long time.) wants to use something other than the recommended 1OZ per gallon (7 gallon fermenter) of starsan. I'm wondering, can I use my mostly full container of 88% lactic acid? If so, what would the dosage be?

Devin said:

http://www.howtobrew.com/appendices/appendixB-1.html

Click to expand...

Neat, thanks.

Lactic acid is not recognized as a passivation chemical, nor is oxalic acid. Typically passivation is done with citric acid or nitric acid. You don't want to mess with nitric acid though because it is very hazardous.

There is a nice product out there called CitriSurf which is good for passivating brew tanks if you want to do it properly.

More info here: http://citrisurf.com/brewery-passivation/

Oxalic Acid which is in Bar Keeper's Friend works perfectly fine to passivate the stainless steel. Just do not use any metal scrubbing pads.

Turkeyshot said:

Oxalic Acid which is in Bar Keeper's Friend works perfectly fine to passivate the stainless steel. Just do not use any metal scrubbing pads.

Click to expand...

Another vote for a good scrub with BKF. It also removes all the oxides from the fabrication process, leaving the surface cleaner than anything else. Since it turns into a sticky paste, it passivates better and faster than Starsan.

IIRC, after the thorough scrub you should leave it covered in the gray BKF paste for 24 hours. Then wash it off, dry, and leave it exposed to air for a few hours. Hope someone can back this up.

IslandLizard said:

Another vote for a good scrub with BKF. It also removes all the oxides from the fabrication process, leaving the surface cleaner than anything else. Since it turns into a sticky paste, it passivates better and faster than Starsan.

IIRC, after the thorough scrub you should leave it covered in the gray BKF paste for 24 hours. Then wash it off, dry, and leave it exposed to air for a few hours. Hope someone can back this up.

Click to expand...

You have me interested.
NOT for my stainless brewing items, I do use BKF and Oxiclean already.

I have some stainless bolts on my motorcycle that are not looking all that great. I will have to give BKF a try. Not sure why I didn't think of it before now.

if it's a brew bucket with volume marks running up it, keep the BKF off of the markings, it will make them fade.

starsan works too. I swear in the SS videos they reccomend not using BKF? Something about it eating away the volume etchings inside?

rekoob said:

You have me interested.
NOT for my stainless brewing items, I do use BKF and Oxiclean already.

I have some stainless bolts on my motorcycle that are not looking all that great. I will have to give BKF a try. Not sure why I didn't think of it before now.

Click to expand...

That should work. Just don't get it on anything else as it's very abrasive and the acid will attack paint surfaces etc. Maybe mask those areas.

I have a fridge and dishwasher with stainless fronts. I also brew in the kitchen, and the dishwasher front always seems to get the brunt, splashed and dripped on with everything, wort, beer, Starsan, you name it.

Recommended for cleaning the SS fronts is this "stainless cleaner" from Weiman (it's a spray...), and regardless of how much I put on or elbow grease I waste on it, it doesn't get either surface even near clean. Then I started using BKF on the dishwasher front, what was there to lose? Well and behold, a good scrub using a soft damp cloth with liberal amounts of BKF does the job. It takes a bit of work but man, does it pay off: Spotless and shiny! The fridge is a little easier target. To finish it off I then put a little of that spray on as it does enhance the shine.

I've used citric acid before and it works very well.

Bar keepers friend is a cleaner, brightener, and rust remover for stainless steel. It works great. But it does not technically passivate and BKF does not to my knowledge make any official claims that it does, unless maybe someone can prove me wrong on that. I am pretty sure they are well aware that their product does not passivate so they don't make that claim.

The ASTM standard A967 which defines passivation only recognizes nitric and citric acid as passivators, not oxalic acid. Furthermore, Coors did a study a few decades back using nitric, citric, oxalic, and a few other acids and concluded that citric did the best job of removing free iron, creating the best passive layer and minimizing the taste of iron in beer. I don't know where that Coors paper is available online, but I received a copy of it when I talked to Stellar Solutions about their CitriSurf products.

TLDR: if you like using Bar Keepers Friend and it works for you when cleaning your stainless, that is great. But you are not technically passivating it.

Palmer says oxalic acid works. I hope he's right!

http://howtobrew.com/book/appendices/appendix-b/passivating-stainless-steel

Horseflesh said:

Palmer says oxalic acid works. I hope he's right!

http://howtobrew.com/book/appendices/appendix-b/passivating-stainless-steel

Click to expand...

He is right that you can use oxalic acid to scour down to bare metal. Alas, scouring down to bare metal still leaves a certain percent of iron because stainless steel is partially composed of iron. It will partially passivate, but not where the bits of surface iron are. Citric acid is a chelating agent which selectively removes iron from stainless to form iron citrate in solution. This leaves behind a chromium enriched layer on the stainless which interacts with the air to form chromium oxide - the passive layer. Oxalic acid is great at removing iron oxide (rust), but not as good at chelating regular iron. That is why passivation should be done with citric acid. Nitric acid removes iron but it is strong enough to also remove chromium, so it doesn't make as good of a chromium enriched surface. There are NO actual passivation standards that specify oxalic acid, nor phosphoric acid, nor any other acid besides citric or nitric.

Oxalic acid is a chelating agent that is used to remove iron from, for example, quartz crystals. Now whether it is as good a chelating agent for iron as citric acid or EDTA or any other chelating agent I can't say. It is certainly more toxic than citric acid.

ajdelange said:

It is certainly more toxic than citric acid.

Click to expand...

Good point! One of the great things about citric acid is that it is very mild and non-toxic. It is the natural organic acid found in oranges and other citrus fruits, after all. Burns like a bugger if you get it in a cut, but very safe to work with.