Citric Acid to Water amounts for passivation

[daphatgrant]

Hey HBT, I've got some new kettles that need to be cleaned and passified. I have some TSP to remove any oils or what not but I'm running into some ratio issues when it comes to the passivation.

I bought citric acid to passivate the kettles but I am having a hell of a time figuring out how much citric acid to use compared to water. According to the cleaning instructions I am supposed to use a 10% mixture of citric acid to water solution. From what I can gather this is to be done by weight/volume. Water weighs 8.34lbs, 10% of that is .834lbs or 13.3oz.

So to get a true 10% mixture using 1 gal of water I'd actually need to use 14.63oz per gal?

I've searched and searched and am not coming up with an easy answer for this, other than just using starsan of course, lol. I'm honestly surprised that a simple ratio like 1-3/4 cup per gal isn't out there already.

I appreciate any help

 

[Bilsch]

The proper mix is a 4% solution so that's 40grams per liter of water or 151 grams per gallon or 5.32 oz per gallon. If you keep your temperature at about 180f your soak time should be about 30 min.
Good writeup about the process here:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110001362.pdf

P.S. Starsan (phosphoric acid) does not/will not passivate stainless steel.

 

[daphatgrant]

The proper mix is a 4% solution so that's 40grams per liter of water or 151 grams per gallon or 5.32 oz per gallon. If you keep your temperature at about 180f your soak time should be about 30 min.
Good writeup about the process here:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110001362.pdf

P.S. Starsan (phosphoric acid) does not/will not passivate stainless steel.

Huh

I'm not saying that I don't believe you but I am getting this right from SSBrewTech's FAQ

"It’s a good idea to passivate your stainless steel equipment with an acid based solution. Filling the vessel with StarSan at 1oz per gallon of water or other acid passivation solution at the recommended strength and at a temperature of 70-80F for 20 minutes, followed by an air dry is all that is needed"

&

"We have received several questions regarding the care and passivation of the stainless steel that virtually every part we sell has an abundance of! While there are several different avenues to reach a final destination, we wanted recognize some of the newly practiced passivation methods.

Remember that passivating stainless steel is a way of renewing the corrosion resistance performance of the base metal and improving it's longevity. It is designed to both remove small free-iron deposits and restore the passive oxide layer that keeps corrosion at bay. Passivation is done after stainless steel has been completely cleaned with TSP to remove any oils or foreign deposits.

While a relatively concentrated dose of Starsan, which is a blend of phosphoric acid and dodecylbenzenesulfonic acid, or Bar Keeper's Friend (Do not apply to electrically etched markings), which is oxalic acid, does work to passivate stainless steel, there are a few other options that work equally as well.

In fact, many recent studies have suggested that citric acid is an excellent alternative to Starsan or Bar Keeper's Friend for passivation. Citric acid is both easy on the environment, and can be more cost effective if frequent passivization is desired.

Lastly, several commercial products have even been introduced to fulfill the needs of passivation for food safe 304/316 stainless, such as Citrisurf. However, citric acid can be purchased in raw form and made into a 10% citric acid/water solution, then heated to 150 degrees for roughly 30 mins to complete the passivation process."

 

[MidAtlanticBrew]

150 vs 180F might make the difference between 4 and 10 percent. A higher concentration won't hurt, it's just wasteful

 

[Bilsch]

I guess the best thing would be to do some googling and see which method you believe works.

 

[daphatgrant]

I guess the best thing would be to do some googling and see which method you believe works.

Again I didn't say that I didn't believe you. What I was asking is if there were a simple formula for citric acid (anhydrous) to water such as 1-3/4 cup acid per 1 gal water to get a 10% solution. I mentioned StarSan and 10% because that's what the manufacturer recommended. The info that you provided me was different from what the manufacturer stated which is why I attached their instructions.

If temp makes a difference in what the ratio should be that would account for your 4% vs the manufacturers 10%. I did not know that the temp would make a difference, let alone a 6% difference, I do now. I looked at FiveStar's product description and as you said StarSan says nothing about passivation. Acid C leaner#5 does however.

I appreciate the formula for 4% at 180F @ 30min I'll use this. I'm new to this and when numbers, times, chemicals, etc don't match up I try to find out why.

Thanks

 

[Bilsch]

No worries. Even in the metal finishing world best practice for passivation is a hotly debated topic. So it stands to reason at this site your probably going to get even a wider range of opinions on the subject.

I gave you my ratio and temp based on a Nasa report however I'm only a chemist not a stainless finishing expert so take it with the appropriate grain of salt.

It is fact that Citric passivation is well known, inexpensive, fast, not toxic or particularly dangerous to you or the environment and works very well. Save your starsan for sanitizing.

 

[daphatgrant]

Hey HBT, I cleaned everything with TSP add a using the formula from above for a citric acid passivation. I've noticed that everything has kind of a slightly sticky residue on it after the acid bath, is this normal? Just clean it with soap and water? Thanks again for all the help .

*Also, do you passivate ball valves as well? I did tsp and citric acid all my SS fittings and quick connects (removed O-rings first.

 

[MidAtlanticBrew]

If it's sticky, you likely did not get all the oil off in the TSP step. I found it necessary to do a double TSP clean on some of my SS Brewtech equipment. As for ball valves, yes passivate but first dissamble and clean really well with a brush and TSP. The valves often have grease to lubricate them. The grease is more challenging then oil to remove. When SS Brewtech first started shipping product, people complained about a solvent taste in their beer even after, two or three batches. I believe the problem was traced to the ball valves

 

[daphatgrant]

If it's sticky, you likely did not get all the oil off in the TSP step. I found it necessary to do a double TSP clean on some of my SS Brewtech equipment. As for ball valves, yes passivate but first dissamble and clean really well with a brush and TSP. The valves often have grease to lubricate them. The grease is more challenging then oil to remove. When SS Brewtech first started shipping product, people complained about a solvent taste in their beer even after, two or three batches. I believe the problem was traced to the ball valves

Thanks! I took apart the ball valves (3-piece style) and soaked and scrubbed them in TSP (minus anything plastic). I'll do the same for the acid bath. I understand what you are talking about in regards to the stickiness from the machining oil but I'm sure that this is from the citric acid. After the TSP soak, rinse and dry everything was normal. I've got an absolute ton of SS fittings, quick connects, nipple, etc that all have a sticky, film (?) on them. It was on the kettles as well and washed right off with soap and water. I'm thinking that my ratio of citric acid to water was off and I used too much citric acid which left a film on everything.

 

[Bilsch]

I never get a film on my parts after the citric soak, they are always squeaky clean. Could your citric powder have gotten mixed up with something else by accident?

 

[daphatgrant]

I never get a film on my parts after the citric soak, they are always squeaky clean. Could your citric powder have gotten mixed up with something else by accident?

Not that I know of, I added the water, brought to 160, dumped in the citric acid, stirred until it dissolved then brought it to 180 and soaked everything for 30min at that temp. I cleaned everything afterwards with regular soap and water and they appear fine now. I think I messed up my the ratio and added far too much citric acid.

While I've been got your attention should I passivate my kegs? They are new and have never been used before.

Thanks!

 

[Dextersmom]

I got the sticky sensation right now as well, but they're also not totally dry yet. I did a double tsp cleaning. Fully disassembled the ball valves. We'll see when they're totally dry. I passivated per ssbrewtech.zendesk.com recommendation of 150 although I was more in the realm of 155 - 160 at times.

 

[Bilsch]

Citric acid is readily and completely water soluble so if the film didn't come off with a water rinse after passivation.. it didn't come from the citric.

 

[Dextersmom]

I'm dumb... Was I supposed to rinse after passivating? SS wasn't specific about that... Lol.

Edit... I know with the starsan it says to air dry and not rinse.

Lol will it matter if I just rinse tomorrow? I'm exhausted right now.

 

[Bilsch]

You'd definitely want to get the citric rinsed off before brewing but it's not a problem to leave it on there overnight.

 

[Horseflesh]

Good writeup about the process here:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110001362.pdf

P.S. Starsan (phosphoric acid) does not/will not passivate stainless steel.

Outstanding link, thanks. I need to repassivate some welds and I'll take NASA's advice.

Regarding StarSan... I have no idea if any kind of dilute solution will work. As another poster said, SS Brewtech does recommend it, and my fermenters from them are still OK.

I did have a surface rust issue on another item. Cleaning with BKF took the rust away... for about a day. Smearing undiluted StarSan on the scratch, holding for a few minutes, and cleaning it off, kept the rust away permanently. <shrug>

Edit to add: if I understand the PDF correctly, for 304 they recommend 4% at 100-140F for 120 minutes. The conclusions on page 40 say that performance on 304 gets worse over 140F, though I did see the other parts that suggested 180F. I just wasn't sure if they were still referring to 304 steel. The document is dense! But the recommendation for 100-140F, 4%, 120 minutes for 304 is repeated on page 49.

 

[helterscelter]

Outstanding link, thanks. I need to repassivate some welds and I'll take NASA's advice.

Regarding StarSan... I have no idea if any kind of dilute solution will work. As another poster said, SS Brewtech does recommend it, and my fermenters from them are still OK.

I did have a surface rust issue on another item. Cleaning with BKF took the rust away... for about a day. Smearing undiluted StarSan on the scratch, holding for a few minutes, and cleaning it off, kept the rust away permanently. <shrug>

Edit to add: if I understand the PDF correctly, for 304 they recommend 4% at 100-140F for 120 minutes. The conclusions on page 40 say that performance on 304 gets worse over 140F, though I did see the other parts that suggested 180F. I just wasn't sure if they were still referring to 304 steel. The document is dense! But the recommendation for 100-140F, 4%, 120 minutes for 304 is repeated on page 49.

is that 4% by weight? volume? I'm no chemist. lol..

 

[Bilsch]

Here is the info from a few posts back..

The proper mix is a 4% solution so that's 40grams per liter of water or 151 grams per gallon or 5.32 oz per gallon. If you keep your temperature at about 180f your soak time should be about 30 min.
Good writeup about the process here:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110001362.pdf

P.S. Starsan (phosphoric acid) does not/will not passivate stainless steel.

 

[Horseflesh]

If you keep your temperature at about 180f your soak time should be about 30 min.

They list different conclusions for 304 steel on page 49 -- 100 to 140F for 120 minutes.

 

[Bilsch]

My take is higher and longer won't hurt so that's what I do. 160-180 for a couple hours. I fill my kettle with every bit of stainless kit I can stuff in there, heat and soak. Then I reheat and dump the solution into my fermenter and let that sit. After I'm done the water is nice and orange. I assume it's ferric citrate.

 

[piojo]

Phosphoric acid does provide some sort of protective coating on mild steel (not passivation). Perhaps it does something similar on stainless? I can't say that it doesn't passivate, but it would make sense that a different protective process is happening.