How to Protect (or Ruin) Your Distillery’s Stainless Steel

Most distillers work around stainless steel every day but know very little about it or how to take care of it.

While stainless is resilient and durable, it can’t look after itself—and, as we’ve covered previously, “corrosion-resistant” isn’t the same as “corrosion-proof.”

Building on an understanding that stainless steel can fail, and that you want to get as many years as possible out of your investment in that equipment, here are some important do’s and don’ts when it comes to everyday maintenance and troubleshooting common problems.

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The Do’s

Visual Inspections

The first and perhaps most important thing that you should do when working with stainless steel in the distillery is to visually inspect the metal before every use.

As its name implies, stainless should never have any blemishes or discolorations on its surface, nor should there be any cracks or unexpected dents. The presence of such issues may be a warning sign that the steel has lacked proper care and may be about to fail.

Most distillers already perform visual inspections of their equipment after every cleaning cycle. During these checks, make sure to examine both the inside and outside surfaces of the equipment for any corrosion, damage, or staining. Also check all weld points on the equipment because these seams tend to show damage first and are often a source of failure.

If you spot an issue, stop using the equipment until that issue is resolved. That often means extra cleaning and re-passivation—however, for cracks or dents, it may be worth consulting an engineer to confirm that the metal’s structure is still sound.

While it may sound basic, a good visual inspection protocol is the best way to identify problems with stainless steel before they get out of hand.

Soft Brushes

Another practice that can extend the life of your stainless is to scrub only with “soft” brushes specifically designed to be used with stainless steel.

These brushes are designed to not damage stainless steel’s passivated layer. As we covered previously, stainless steel is resistant to chemical attack thanks to a very thin cover of chromium oxide known as the passivated layer. That coating is only a few molecules thick, but it’s incredibly resistant to attacks by oxygen and strong chemicals. It is, however, susceptible to abrasion damage—which can easily come from wiry or “hard” scrubbing tools such as steel wool.

Be careful to only use brushes that are designated safe to work with stainless. They may cost a little more and require a little more elbow grease when scrubbing a trouble spot, but they do not damage the passivated layer, ensuring the lifespan of the stainless steel.

Reduce Free Iron

Finally, another thing to consider when caring for stainless is to minimize its exposure to free iron.

Free iron, or unalloyed iron, is a catch-all term for elemental iron that’s not already bound up by an existing molecular structure as part of the stainless steel. Free iron can come from almost anywhere, but it can often transfer from nonstainless metal tools or cleaning brushes that have been in contact with elemental iron.

Once free iron builds up on the surface of stainless steel, it will begin to rust, which then makes the stainless more susceptible to certain types of chemical attack while opening the door to contamination issues. That’s why reducing the amount of free iron on stainless is incredibly important.

To prevent a buildup of free iron, most distillers have dedicated brushes and tools that can be used only on stainless-steel equipment. That helps to limit the possibility of free iron, though it does not eliminate it. Some distillers go as far as to require special suits when cleaning stainless steel, further reducing the possibility of cross-contamination from clothing—although that’s not commonly required.

If you suspect that your stainless has been contaminated with free iron, you can perform either a ferroxyl or copper sulfate test; either test will reveal free iron’s presence at very low levels. You can remove free iron from stainless steel by administering a pickling solution. The most common pickling solutions are made of a mixture of hydrofluoric and nitric acids, which should be able to remove the free iron from the stainless in as little as 30 minutes.

However, be aware that pickling solutions are often extremely strong and should be handled with the utmost care.

The Don’ts

Temperature Stress

The first and most important thing to avoid with stainless steel is exposure to extreme or uneven temperature swings.

Stainless steel is robust, but rapid and uneven temperature swings can cause a phenomenon known as thermal shock. Thermal shock warps the stainless, weakening it and damaging the passivated layer, thus shortening the metal’s expected lifespan. Furthermore, thermal shock can increase the likelihood of forming a stress corrosion crack, which will affect the metal’s basic crystalline structure and render it completely unusable.

That’s why you should never try to rapidly heat or cool your stainless equipment and why you should always keep it away from open energy sources that might rapidly transfer heat.

Chipping

A second thing to never do when working with stainless steel—and this may be the most obvious—is attempt to chip off troublesome residue.

Again, the passivated layer of stainless is incredibly thin and vulnerable to abrasion. Using any sort of edged tool—even a soft plastic one—to remove debris from the surface will inevitably damage that passivated layer, making it vulnerable to corrosion and rust.

Furthermore, when attempting to chip away debris—and I’ve observed this on countless occasions—distillers often step into or onto their stainless-steel equipment. This is a hazard—our boot heels are often covered in bits of metal, chemicals, and other objects, which further damage the passivated layer and may even cause pitting in the stainless itself.

That’s why we should use only chemical cleaning agents and the aforementioned “soft” brushes to remove debris from the surface of stainless steel.

Chlorine and Other Chemicals

Finally, the thing that may be the foremost danger to stainless steel in the distillery is exposure to chlorine.

As any high-school chemistry student should know, chlorine is an incredibly strong oxidizing agent commonly found in many chemical cleaners, including bleach. When chlorine (in the form of a chloride anion) touches stainless steel, it attaches itself to imperfections in the passivated layer. Through a process known as galvanic corrosion, it begins to form a pit. As that pit grows, it draws more chloride into it, and it will deepen at an exponential rate and compromise the structural stability of the stainless steel.

Depending on several factors, including pH and temperature, that can be an incredibly rapid process that’s difficult to detect until it’s too late. Notably, chlorine isn’t the only chemical that can do this—there are many others that can be just as damaging, if not more so, to stainless steel. It’s important to always confirm that any chemicals you’re using in and around the distillery don’t contain anything that could harm stainless. There are few things worse than having to buy new equipment because someone used the wrong cleaner.

Beer Stone

No article on stainless-steel care in the distilling industry—or in brewing—would be complete without at least a mention of beer stone.

Calcium oxalate, or beer stone, is one of the most common problems that distillers run into when caring for stainless long-term. A whitish-yellow crystalline chemical, calcium oxalate (CaC₂O₄) forms when free calcium ions come into contact with oxalic acid from grain. The resulting reaction creates crystals that can attach themselves to stainless steel, forming a jagged surface that can catch proteins and other organic matter.

That layer greatly diminishes the heat-transfer coefficient of the stainless, affecting the steel’s ability to cool or heat properly. What’s more, as these crystals grow larger, pockets begin to form in which spoilage microbes can survive. That renders the stainless steel effectively impossible to sanitize, and it can also have deleterious effects on the lifespan of the stainless.

Preventing beer stone on stainless is mostly a matter of taking the right precautions. Good cleaning practices and operator vigilance are the first lines of defense in preventing buildup. Periodic cleaning of the stainless with both caustic and acidic cleaners designed to prevent and remove beer stone should be standard practice for all distillers, regardless of size.

The frequency and intensity of these cleanings can depend on the distillery and type of equipment. Because beer stone is most likely to form on surfaces that are exposed to wash, distillers should keenly monitor their fermentors and mashing equipment for signs of buildup. Also, be aware that if you’re using caustic soda for cleaning in a CO₂-rich environment, there is an increased risk of beer stone formation. Best practice is to evacuate all CO₂ from any stainless vessel that’s scheduled to be cleaned.

Though often overlooked, maintaining stainless steel is an important part of any distiller’s job. If you’re not properly caring for your stainless, you’re not only risking financial loss but also the health and safety of others.