How To Passivate Brewing Vessels

It seems a lot of new breweries in Asia are searching the term “How to passivate brewing vessels?” There are new breweries popping up all over Asia.

The resulting purchase of equipment in places from Bali to Hong Kong means there a lot of brewing tanks in need of passivization.

If you want to make sure your new brewery isn’t brewing beers with off-flavors such as metal. Then you need to passivate your brewing tanks prior to brewing your first batches of beer.

N.B. You also need to passivate brewing tanks every 6 month or so too to maintain your brewing equipment depending on which process you use.

Today we are going to discuss how to passivate your current tanks if you’re an older brewery. Then we will explain how to passivate brewing vessels if you have new equipment installed.

How To Passivate Brewing Vessels
Keeping Your Brewery Clean

So, What is Tank Passivation?

In our article how to passivate brewing vessels we should really start with what passivation is.

In brewing it is the process of chemically treating stainless steel. Most brewing tanks are made stainless steel these days.

The aim is to create an invisible layer or coating on the inner tank walls so the metal will not be susceptible to corrosion and pitting caused by:

  • Cleaning chemicals (acid, caustics and sanitizers)
  • Carbon Dioxide and beer
  • Chlorides (like salt) that can be very hard on stainless steel
  • Beer with low pH

There are other causes of corrosion but these are the main ones. Before we dive deeper into passivation, we need to look at descaling/pickling.

What is Descaling and Pickling?

Descaling and pickling should not be confused with passivation. With older tanks you will get buildup of deposits which need removing (oxide removal).

Before we can even discuss how to passivate brewing vessels you must first clean down to the bare metal to ensure the passivation is successful.

Pickling Brewing Vessels
An Example of Pickling Steel Before and After

The use descaling and pickling on metal is to remove oxides from stainless steel. Strong acids such as hydrochloric acid, hydrofluoric acid, sulfuric acid or nitric acid are used in descaling.

The Old Way – Traditional Passivation

The two chemicals often used in this older method. They are citric and nitric. Citric acid is mild organic acid and is good at chelating iron, but doesn’t itself leave a protective coat behind to protect your tank.

Using citric acid will leave your tanks susceptible to chemical attack when you further clean your tank after use. Brewers most often opt for nitric acid when they’re passivating tanks.

Nitric acid is used in high concentrations (roughly 20% or higher). Using 20% nitric acid you will CIP your tank for an hour and then drain the tank (can be used again in another vessel – but check the concentration).

After the CIP you will allow the tank to air dry for 24 hours (keep the tank man-way open). This allows time to create an invisible chromium oxide layer to protect the metal.

The main problem with this method is that the layer isn’t permanent and often not repeated in a brewery. Due the dangers of using nitric in such dangerous concentrations.

You need to passivate your tanks at least twice a year with the method described above. The newer way we describe below will help keep your tanks clean and in tip-top condition on an ongoing basis.

How to Passivate Brewing Vessels – The New Safer Method

The exists a new way to passivate your tanks and keep them in good condition, flavor-neutral and shiny. The new method doesn’t involve using dangerous chemicals in high concentrations.

Please also note, that acid cleaning and drying to form a chromium oxide layer no longer works as well as they once did either. It can lead to “flash rusting” (iron deposits) around vulnerable point in your tank (like welds).

How To Passivate Brewing Vessels
Rust around welds

This new method using nitric acid followed by a non-caustic alkaline cleaner is becoming more widely used in the brewing industry. It is best way to keep your metal clean AND passivated.

Conversion Coating Passivation

The idea of cleaning with acid first and then following with an alkaline cleaner seems counter-intuitive to most brewers.

The common method is caustic, rinse, acid and final rinse of tanks. This method is great for removing protein soiling but less effective on beer stone and doesn’t properly passivate metal over time.

In time the result lead to soil build up and the metal can develop microbial corrosion (MIC). Allowing this to continue can lead to metal pitting and put you at higher risk of infections. As it is harder to properly clean and sanitize your tanks.

Below we outline the method many brewers have now turned to that allows them to keep their tanks in the best condition possible.

How to Passivate Brewing Vessels – The Procedure

Note: This procedure is for tanks already in your brewery and have been used. For new vessels we cover it later in this post.

  1. Rinse excess soil if necessary (with hot water 60-70C).
  2. Make up a 2% solution of water with a nitric phosphoric acid blend (make sure it is pH 2 or lower).
  3. Recirculate this liquid through spray-ball (CIP) for a minimum of 15 minute at a maximum temperature of 140F (60C). You want the nitric acid in the solution not the air.
  4. Drain the solution BUT DON’T RINSE!
  5. Depending on the soiling make a 2-3% solution of non-caustic alkaline cleaner that contains either hydrogen peroxide or sodium percarbonate.
  6. Recirculate through spray-ball at between 120-140F (50-60C) for 15-30 minutes.
  7. Drain the solution and IMMEDIATELY move onto step 8.
  8. Rinse the tank with the water (if possible, with potable water the same temperature as in step 6).
  9. Check the pH of rinse water and inner tank wall if possible, waiting for the pH is neutral (around 7). When pH is neutral passivation is complete.

How to Passivate Brewing Vessels – Working with New Tanks

When you have a delivery of new equipment delivered to your location. Be it made in China or elsewhere. Often there is residue left over inside the vessel from the manufacturing process.

You can see unwanted machine oil, dirt and debris left over from working on the tank. The first move is to give the tank a hot water rinse to drain to make sure there aren’t pieces of metal or dirt that could break the cleaning pump.

We recommend a non-chlorinated liqud built caustic CIP Cleaner. It remove machine oil and debris (use a 3% solution at 60-80C). You then follow the caustic CIP with a hot water rinse to you have neutral pH.

If you see any signs of surface rust then a citric acid CIP (2% solution) is an easy way to remove this rust. Followed by the obligatory rinse to neutral.

Your tank is then ready for the 9-step routine outlined earlier.

So, pre-steps are:
  1. To remove any unwanted machine oil, dirt and debris left over from working on the tank. Use a 3% solution of a heavy-duty, non-chlorinated liquid alkaline built CIP cleaner at 140-175F (60-80C) for 15-30 minutes.
  2. You can then drain the liquid and rinse immediately. Do a visual inspection to make sure all unwanted dirt has been removed. If there is still some residual dirt repeat step 1.
  3. When there’s no dirt left, you can do a citrus acid CIP. If you see any signs of surface rust. Make a 2% solution and recirculate through the spray-ball at 120-130F (50-55C) for 15-30 minutes. Then rinse well.
  4. After rinsing the citric acid, you can begin the CIP with a phosphoric/nitric acid blend followed the non-caustic cleaner using the method explained below.
How To Passivate Brewing Vessels
We All Like Shiny Tanks!

The Passivation of New Vessels

  1. Rinse your vessel with ambient to warm water.
  2. CIP with a 2% solution of a nitric/phosphoric acid blend at 120-130F (50-55C) for 15-30 minutes.
  3. Drain the vessel but do not rinse the tank.
  4. Using a 2% solution of a phosphated, silicated and oxygenated non-caustic acid cleaner CIP for 15-30 minutes at 120-140F (50-60C).
  5. Rinse well till you have neutral pH rinse water.
  6. The passivation of the tank is now complete.

Conclusions

Keeping your tanks passivated will help your beers be the best they can be. If you are unsure about what chemicals to use in this process then your chemical supplier should be able to help.

To carry out an acid clean, draining but not rinsing then followed immediately by an alkaline cleaner is what metallurgists call phosphate/silicate coating.

This passivation technique is different to the high concentrate nitric acid method that leaves a chromium oxide layer on the metal.

The phosphate/silicate coating method offers some passivation properties but without the use of dangerously high concentration of chemicals and with time savings as you do not have to air dry for 24 hours too.

It is safer, easier and will keep your tanks clean and passivated on a ongoing basis.

If you would like to have an offline copy of this article then we have made a pdf which you can access by clicking here.

Neil Playfoot

Neil is a brewer with 25 years international brewing experience. Based out of China (first came in 2010) he works as a brewing consultant helping brewers with their projects and brewing processes. To find out what services Neil can provide your brewery please click here. If you'd like to contact Neil you can email at neil@asianbeernetwork.com.
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