Cleaner at the Brewery Part 2
Passivation? We don’t have time for that.
Today I want to talk about passivation of stainless-steel equipment at the brewery. We know it’s important. We know that new stainless equipment is generally passive when it arrives at the brewery. We know that strong acids are involved… and let’s be honest, we know that we don’t want to passivate equipment unless we really need to. But what is passivation, exactly? Why is it so important? When does equipment need to be passivated and how do we do it? In part 2 of my Cleaner at the Brewery series, I’ll answer these questions and share some useful info that will help you determine when it’s time to passivate at your brewery.
So, what is passivation? Simply put, passivation is the process of returning stainless steel to a passive state. Ok, your right- that’s not telling you much. Let me go on. The surface is said to be “passive” when it is covered with molecular oxygen in the form of metallic oxides. With stainless steel, that layer or film is mostly made of chromium oxide. Stainless steel is made up of nickel, chromium, iron, and a small amount of other metals. In food and beverage manufacturing, we are usually talking about 304 or 316 stainless steel. Both have higher chromium content which aids in maintaining a corrosion resistant chromium oxide layer. The passivation process involves removing any free iron from the surface to allow the formation of more corrosion-resistant oxides of chromium and nickel.
Generally, new stainless-steel equipment is already passivated when it gets to the brewery. At least, we can assume that the sheet stock that your fabricator used was passivated. But what about the equipment as delivered? A local tank fabricator may not have the ability to passivate the tank after welding. In addition, the tanks may arrive with machine oil, dust, or a number of other soils that need to be removed before passivation, but I’ll discuss that in a bit. Passivation is also necessary after new installation of process piping or any modification to existing piping, such as adding instrumentation or divert panels. Not just welds but any area near the weld that might have been exposed to high heat may need to be treated. Localized discoloring would indicate exposure to high heat and that the surface is no longer passive. Also, any dulling or browning of stainless steel over time would indicate iron at the surface. In these cases, you want to repassivate the equipment.
Before passivating, surfaces need to be clean. This is very important. The acid used for passivation must have good contact with the entire surface. Any soil should be removed with a caustic solution of Pursuit RSTM. New vessels often are covered with machine oil, dust from grinding, and other soils. The use of a degreaser such as D-Solv 501TM will remove these types of soils.
To passivate, a solution of 20-25% by volume of nitric acid is typically used. A nitric phosphoric acid blend is often used and applied by a CIP device at temperatures up to 160˚F. I recommend Pass ECNTM at a 1:2 acid to water ratio. The time required ranges from 30 minutes to 2 hours depending on temperature. If you are able to achieve temperature of at least 145˚F, passivation of the stainless steel may only require 45 minutes to an hour. Because passivation with nitric acid involves high temperatures and at high concentration, it’s recommended that you consult with your ProActive Solutions USA representative before passivating and remember to wear appropriate PPE.
Alternatively, an 6-10% by weight solution of citric acid can be used to passivate. Citric acid is less aggressive than nitric so it is often used when there is a concern about nitric or phosphoric acid in the waste stream. Passivating your brewery equipment with citric acid can be done at ambient or slightly elevated temperatures, so if your unable to maintain the higher temperatures needed for passivation with nitric acid, then citric acid would be a good choice. However, since citric acid is not as aggressive as nitric acid, longer times may be needed. And unlike nitric acid, citric acid does not oxidize the chromium or nickel, so the vessel must be allowed to air dry following a quick rinse to allow enough contact time for oxidation prior to putting equipment into service.
Whether it’s your brew kettle, mash tun, lauter tun, fermenter, brite tank, or process piping, there are a number of good reasons to keep your stainless equipment passive. Everyday soil from brewing, fermenting, cellaring, and packaging processes can more easily be removed and rinsed away when stainless steel surfaces have a uniform layer of chromium oxide achieved through proper passivation. Beer can be stored for long periods of time in an oxygen-free, CO2 environment without corroding your equipment or picking up metallic off-flavors. Let’s not forget about the longevity of equipment. You can avoid premature replacement of equipment by keeping it clean and maintaining that passive layer of chromium oxide.
In summary, maintaining that passive layer on your brewery equipment is important for beer quality, can improve chemical and water efficiencies, and prolong the life of your equipment- all adding up to a strong bottom line for your brewery today and for years to come.
Stay tuned for my next two topics in this 4-part series where I’ll be discussing centrifuges and scale removal of your HLT vessels. Until then, stay safe and happy brewing!
Food Quality Specialist – ProActive Solutions USA
Steve has over 10 years of leadership experience in the brewing industry providing expertise in operations, quality management, logistic planning, and product development. As a former brewmaster, his knowledge and experience in CIP systems, sanitation, and process improvement are rooted in his passion for crafting high quality beer. Degree from University of Wisconsin- La Crosse in Biology.
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