Passivated Stainless Steel Beer Brewing Equipment

Brewing equipment is often made of high-grade stainless steel. Craft brewers, homebrewers, wineries, and distilleries all know the importance of "passivating" their tanks and equipment. Quality is paramount, and so is proper handling. Although stainless steel is known as the ideal metal for brewing beer, it can also corrode or rust.

Stainless Steel and Rust Prevention

The chromium in stainless steel reacts strongly with oxygen, forming a protective layer of chromium oxide on the steel's surface. This chromium oxide protects against rust and corrosion. However, if the chromium layer is compromised for any reason, the iron in the steel may actually begin to corrode and rust.

Stainless steel brewing equipment is generally very corrosion-resistant. However, this protective layer can wear away if it comes into contact with bleach or other bleach-containing cleaners, is scratched, scrubbed, comes into contact with non-stainless steel scouring pads (such as steel wool), or comes into contact with ordinary steel.

What is beer can passivation?

The beer brewing process involves chemically treating stainless steel. Today, most beer cans are made of stainless steel. Its purpose is to create an invisible coating on the inside of the can, protecting the metal from corrosion and pitting caused by:

• Cleaning chemicals (acids, caustics, and disinfectants);

• Carbon dioxide and beer;

• Chlorides (such as salt) are very corrosive to stainless steel;

• Beer with a low pH;

• There are other causes of corrosion, but these are the main ones. Before delving into passivation, we need to first understand descaling/pickling.

What is descaling and pickling?

Descaling and pickling should not be confused with passivation. Older beer cans can accumulate deposits that need to be descaled (removing oxides). Before discussing how to passivate a beer can, you must first clean the exposed metal to ensure a successful passivation.

Traditional Passivation

This age-old method often uses two chemicals: citric acid and nitric acid. Citric acid is a mild organic acid that effectively chelates iron, but it doesn't leave a protective layer on its own to protect your cans. Using citric acid makes your cans susceptible to chemical attack during subsequent cleaning. Brewers often opt to use nitric acid to passivate their cans.

The main issue with this method is that the protective layer isn't permanent and typically doesn't regenerate within the brewery. Due to the dangers of using such hazardous concentrations of nitric acid, you'll need to passivate your cans at least twice a year using this method.

Conversion Coating Passivation

For most brewers, the idea of cleaning with acid followed by an alkaline cleaner seems counterintuitive. A common approach is to use an alkaline wash, rinse, acid wash, and finally rinse the tank. This method is very effective for removing protein scale, but is less effective against beer stone and does not passivate the metal over time. Over time, this leads to scale accumulation and microbiologically-induced corrosion (MIC) of the metal. If this condition persists, it can cause pitting corrosion and increase the risk of infection. This makes cleaning and disinfecting the tank more difficult.

What happens if you don't chemically passivate?

You're not doing your best to brew the best beer possible. We understand that for most brewers, purchasing stainless steel equipment is an investment that will ensure the best beer. We recommend taking this step to ensure your equipment is properly cared for and lasts for years to come.

When should passivation be performed?

For new equipment, much depends on where it's made. High-end equipment is often soaked in nitric acid during the final production step and may only require a thorough cleaning to remove residual oils before first use. In either case, a thorough cleaning is necessary to remove oils, polishes, and other contaminants that could damage beer. The extra step of passivation after cleaning isn't expensive, as stainless steel equipment is expensive and has a long lifespan. Additionally, if you brew beer, passivation every other year is a good preventative measure.

How to passivate brewing vessels?

• Remove any oil, dirt, and debris from working on the fuel tank.

• You can then immediately drain the fluid and rinse. Perform a visual inspection to ensure all dirt has been removed. If dirt remains, repeat step 1.

• If there is no dirt, perform a citric acid cleaning-in-place (CIP) procedure. If you notice any signs of surface rust, prepare a 2% solution and circulate it through a spray ball at 120-130°F (50-55°C) for 15-30 minutes. Then rinse thoroughly.

• After rinsing with citric acid, you can first perform a CIP using a phosphoric acid/nitric acid mixture, followed by a non-corrosive cleaner as described below.

Passivation of the Container

• Rinse the container with room-temperature water.

• Cleaning in place (CIP) is performed using a 2% nitric/phosphoric acid solution at 50-55°C (120-130°F) for 15-30 minutes.

• Empty the container, but do not rinse the tank.

• Cleaning in place (CIP) is performed using a 2% phosphate, silicate, and oxidizing non-corrosive acid cleaner at 50-60°C (120-140°F) for 15-30 minutes.

• Rinse until the rinse water has a neutral pH.

• The tank passivation is now complete.