[brewinhard]

Citric Acid at the rate of 5.32 oz/gallon. Heat to 160-180F for 2 hrs. Rinse well with hot water, then let air dry for minimum of 24 hrs with 48 being best. Recently did it to my kettle and placed all miscellaneous SS items in there as well. Then reheated to 180F and drained into two kegs to passivate them as well. Not hard to do.

[denny]

This is very interesting.  I had never been aware that SS needed to be passivated at all.

[LeeH]

Oxygen does the passivation. Nitric acid cleans the surface and supplies Oxygen. Citric acid? Anyone know.

A clean surface of SS will passivate quickly when exposed to air.

How long does it take when just using air?


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It is a rapid reaction. Minutes or less.

I’m confused, if it takes minutes in air why do we need nitric acid?


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[hopfenundmalz]

Nitric acid does agressive cleaning and supplies Oxygen.

Here is John Palmer's take
http://howtobrew.com/book/appendices/appendix-b/passivating-stainless-steel

[ynotbrusum]

I didn’t know it, but I deep clean every year to remove Beer stone with Bar Keepers Friend (oxalic acid), so Ihave repassivated in that process.  It is nice to see the kettle shine like new!

[Bilsch]

Passivation has two parts, first removing the free iron and enriching the chromium layer and then secondly oxidizing that chromium to create the 'stainless' surface. Nitric acid works well because it does both at the same time but is nasty to work with and dispose of properly. Citric is great for removing the iron but is not an oxidizing acid but that's not a problem since oxidation happens later during exposure to air. Citric is much nicer to handle.

[MNWayne]

So... my take on this is, it's something to talk about, but nothing to worry about.

[klickitat jim]

So... my take on this is, it's something to talk about, but nothing to worry about.

As is at least 50% of brewing...

[ynotbrusum]

So... my take on this is, it's something to talk about, but nothing to worry about.

As is at least 50% of brewing...

It is that 50% that keeps us talking!  And listening.....

[The Beerery]

So... my take on this is, it's something to talk about, but nothing to worry about.

If you don't care about fenton reactions it is nothing to worry about. If you do, it is. Simple as that.

[Joe Sr.]

So... my take on this is, it's something to talk about, but nothing to worry about.

If you don't care about fenton reactions it is nothing to worry about. If you do, it is. Simple as that.

Seems like that's going a little far. As long as you care for stainless it shouldn't need to be re-passivated. If it needs to be, it's a relatively simple process as long as it's cleaned with an appropriate acid cleaner.

Your stainless shouldn't un-passivate from standard use.

But do whatcha like.

I've only worried about it after drilling a kettle and with new to me used kegs.

[JT]

Great thread.  A while back my boil coil was dry fired.  It got hot... to the point I thought I had opened a portal for Lucifer himself to ascend upon earth. 
When I peered into the kettle I saw the coils glowing cherry red and orange.  After they cooled the coils were purple.  I scrubbed em, star san'd em.  Purple. 
Just purchased some barkeepers friend.  Used as directed with soft cloth.  Purple.  Scrubbed harder and changed to blue scrub pad.  They turned blue!  And some brown gunk was forming on the pad.  Traded the blue pad for green scotch brite.  By God there is stainless steel underneath there.  I tried to take this pic halfway through scrubbing.  Top and bottom coils have received some treatment, middle coil yet to go. 

[Richard]

Yes, BKF is great for cleaning electric heating coils that have burnt on residue (I know from personal experience), but that has nothing to do with passivation. Let me repeat what I said above:

Passivation is to prevent rust. If you don't have any rust then you don't need to passivate. It is that simple.

[JT]

Yes, BKF is great for cleaning electric heating coils that have burnt on residue (I know from personal experience), but that has nothing to do with passivation. Let me repeat what I said above:

Passivation is to prevent rust. If you don't have any rust then you don't need to passivate. It is that simple.

Not sure this is entirely accurate.  The blue oxide layer I saw on my coils are not passive and would lead to rusting IIRC.  Cleaning them down to bare metal with BK Friend should allow the steel to re-passivate itself.