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**lthendricks8** · 05-01-2016, 09:50 AM

Originally posted by bpdevlin View Post

Is anybody here using just citric acid as a descaler / caustic neutralizer in fermenters?

I've been using it for minor passivation & cleaning jobs (in a spray bottle), and it seems to remove minerals reasonably well. I will follow each acid rinse with PAA, so I assume there won't be any flavor left on the beer.

I use it for passivation, but only because I can't get my hands on nitric where I am without going through a ridiculously ornate and overly complex licensing process. It's relatively inexpensive, but you have to use about five times as much or run everything at a higher temperature/longer times. I use it in conjunction with phosphoric for acid rinses on my equipment post caustic every few cycles. But I'd much rather have nitric.

**Tim DHBC** · 05-31-2016, 05:24 PM

I came across this article from NASA about passivating 304 Stainless with Citric Acid. From what I could understand it seams that a 4% solution at 140 for 2 hours worked well. Anyone else have any information on this?

Citric Acid Passivation of Stainless Steel - NASA Technical Reports Server (NTRS)

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110001362.pdf

Passivation is a process for cleaning and providing corrosion protection for stainless steel. Currently, on Kennedy Space Center (KSC), only parts passivated with nitric acid are acceptable for use. KSC disposes of approximately 125gal of concentrated nitric acid per year, and receives many parts from vendors who must also dispose of used nitric acid. Unfortunately, nitric acid presents health and environmental hazards. As a result, several recent industry studies have examined citric acid as an alternative. Implementing a citric acid-based passivation procedure would improve the health and environmental safety aspects of passivation process. However although there is a lack of published studies that conclusively prove citric acid is a technically sound passivation agent. In 2007, NASA's KSC Materials Advisory Working Group requested the evaluation of citric acid in place of nitric acid for passivation of parts at KSC. United Space Alliance Materials & Processes engineers have developed a three-phase test plan to evaluate citric acid as an alternative to nitric acid on three stainless steels commonly used at KSC: UNS S30400, S41000, and S17400. Phases 1 and 2 will produce an optimized citric acid treatment based on results from atmospheric exposure at NASA's Beach Corrosion Facility. Phase 3 will compare the optimized solution(s) with nitric acid treatments. If the results indicate that citric acid passivates as well or better than nitric acid, NASA intends to approve this method for parts used at the Kennedy Space Center.

**dick murton** · 06-01-2016, 03:20 AM

I found an article by or on behalf of ASME (or some such) and also this one http://www.bssa.org.uk/topics.php?article=68

But I think the original question was about caustic neutralisation. I have not used citric acid for this role, but acid detergents, whether nitric or phosphoric based, are a blend of acids and surfactants etc, so will do the job more effectively than simple non blended acids of any sort. Nitric and phosphoric detergents may also be combined with sanitising agents, so although you have to rinse, you don't have to use PAA or similar, so you save time, water and perhaps a little reagent money (oh, and they are a little easier to handle than PAA). I would have thought that straight citric acid usage would mean it is actually more expensive to use overall, but obviously I can't confirm that from experience.

**roc-craven** · 06-03-2016, 11:26 AM

I know the NASA engineer in the report. If you have any specific questions I can ask him for you.

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Citric acid as an acid rinse?

Citric acid as an acid rinse?

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