By:
Dana Johnson, Technical Manager, Diversey – A Solenis Company
Dana Kapron, National Business Development Manager, Five Star Chemicals & Supply Inc.
Robert Meehan Ph.D., Head Brewer, Living the Dream Brewing
While stainless steel is a workhorse of modern brewing, keeping it in pristine condition takes
more than just a CIP cycle and good intentions. Without proper care, brewery tanks can slowly
introduce corrosion and off-flavors, and may lead to loss of product. In order to keep tanks in
working condition, regular passivation must be performed.
Yet, passivation of stainless steel is not well understood by many in the brewing community.
This is largely due to varying and sometimes conflicting information on the subject. What is
passivation? Why is passivation important for both brand-new stainless-steel tanks and ones
that are already in service? This article will describe what passivation is, what chemicals and
procedures are often used and will detail a new method of passivation that is safe, repeatable,
and offers better protection against chlorides than the traditional chromium oxide passivation.
Passivation is defined as the chemical treatment of stainless steel and other alloys to produce a
corrosion-resistant layer. Acids, sanitizers, salts, CO2, and even beer itself, can wear down this
protective layer, leading to pitting, rust, and potential beer-spoiling contamination
Nitric acid used in high concentration (about 20% active or more) is the most well-known,
traditional method of passivation and, when followed by a 24-hour air dry, creates an invisible
chromium oxide (Cr203) layer to protect the metal. A problem with this method is that it is not
permanent and is rarely (if ever) repeated in the brewery due to the hazards of using an
extremely dangerous concentration of nitric acid and time constraints.
Citric acid is a mild, organic acid and offers better efficacy in chelating free iron, limiting rust
development, a major consideration in passivation. It’s significantly safer to handle,
environmentally friendly, and doesn’t require the same level of personal protective equipment or
ventilation as nitric acid. While citric acid doesn't create as thick an oxide layer as nitric, it
provides effective corrosion resistance and is particularly useful for smaller breweries, periodic
maintenance, or where regulatory or facility limitations make nitric use impractical.
Lastly, using a nitric/phosphoric acid blend, immediately followed by an alkaline non-caustic
cleaner, first detailed in The New Brewer (Noncaustic Cleaning in the Brewery, March/April,
1996), is one of the best ways to not only keep the metal clean, but passivated at the same
time. This method forms a phosphate/silicate conversion coating that protects the stainless
surface and creates a glassy-smooth finish, less prone to harboring beerstone or organic
buildup. Many breweries that adopted this cleaning regime over 30 years ago still use it,
regardless of whether they’ve outgrown their original equipment or not.
Conversion Coating Passivation
Following the acid with non-caustic alkaline cleaner may seem completely foreign at first to
brewers who consistently use the caustic-rinse, acid-rinse method of cleaning their tanks.
While the tried-and-true method works well to remove protein soil, it tends to be less effective on
beerstone and does not properly passivate the metal. Over time, soils can build up, and the
metal can develop microbial induced corrosion. If left unchecked, these deposits can pit the
metal. The process of prepping and passivating new and existing equipment is essentially the
same, though new equipment may require extra cleaning to remove machine oil, dust, debris,
and rust from the manufacturing
1. CIP with 1-2oz non-chlorinated caustic per gallon of hot water (140-180° F) for 15-30
minutes.
2. Drain and rinse well.
3. If there is any surface rust visible, CIP using a 2 oz. citric acid per gallon of 120-130° F
water for 15-30 minutes
4. Drain and rinse well.
1. CIP with 2 oz. of nitric/phosphoric acid blend per gallon of 120-130°F water for 15-30
minutes. [Do not exceed 140° F] to keep the nitric acid in the solution.
5. Drain, but do not rinse.
6. CIP with 2 oz. of non-caustic alkaline cleaner, that contains either hydrogen peroxide or
sodium percarbonate, per gallon of 120-140°F water for 15-30 minutes.
7. Rinse well until the effluent water pH is neutral
Below are before and after images of what a tank, post-cleaning and passivation:
How often should you passivate?
Most breweries should passivate tanks at least once a year, though breweries with hard water, high-use fermenters or tanks exposed to acidic/sour beers may need it every 3-6 months. Anytime a tank undergoes repairs, aggressive scrubbing, or experiences a contamination issue, it’s time to re-passivate.
Conclusion
Every brewer knows that keeping brewing equipment cleaned and sanitized is the key to making the beer taste its best, batch after batch. Passivation doesn’t just protect your stainless steel, it protects your beer, your flavor stability, and your bottom line. Whether you’re brewing on a pilot system or running a full-scale production facility, giving your tanks a proper passivation treatment is one of the simplest investments you can make in long-term quality and consistency. Consult your chemical provider for their recommendations to keep your equipment not only cleaned but passivated, too.
Key Ideas:
For more information on passivation, please visit the following links:
https://www.birkocorp.com/resources/blog/care-feeding-of-stainless-steel-for-new-existing-tanks/
Cleaning Under Pressure – Colorado Brewers Guild
