What is stainless steel?
Stainless steel contains a mixture of alloy metals such as chromium or nickel. Stainless steel however, contrary to popular belief, is not the same as galvanized steel (which contains a layer of zinc on the surface).
The 3 most common reasons for stainless steel corrosion are:
- Abrasion – a rough or sharp object that scratches the surface of the stainless steel element
- Water – hard water (water with a high mineral content) deposits that are not wiped away
- Chlorides – salt, food preservatives and even industrial cleaners
In regards to stainless steel in the foodservice industry, there are two main classifications – the 400 series and the 300 series.
The 400 series has chromium mixed in with the stainless steel and the 300 series contains chromium and nickel in its stainless steel composition.
304 – as mentioned above, AISI 304 (along with the rest of the 300 series) contains a chromium-nickel mixture that is easy to form with an excellent resistance to corrosion. AISI 304 would be used for the exterior of refrigeration, benchtops, etc.
430 – another common specification has a much lower resistance to corrosion than the AISI 300 series and is more commonly used for interior use – such as componentry inside refrigeration.
Basically, these additional metals provide the protection that prevents the corrosion of untreated steel that would normally occur over time or due to direct exposure of reagents.
Due to the additional metals being such a small percentage of the overall makeup of the stainless steel element, the protective “layer” can be easily damaged if not cared for properly.
Why maintain stainless steel?
After a brief explanation about how stainless steel is formed and its uses, understanding why maintenance of stainless steel is a crucial step in ensuring the longevity of your commercial kitchen equipment and appliances.
Atmospheric conditions can significantly impact the condition of your stainless steel if left uncared for. This can include humid and moist environments such as a poorly ventilated kitchen and even the use of commercial cleaner vapours (indirect contact with the stainless steel surface).
Types of cleaners & methods
One of the advantages in stainless steel is its ability to withstand repeated cleaning and that the chromium layer will not “dissolve” over time.
Method 1: using a damp cloth with a mild detergent, wipe with the grain of the finish (some stainless steel surfaces have a brushed finish or grain). Never scrub across the grain as this can damage the stainless steel finish.
Method 2: for baked-on grease, use baking soda. Water and detergent are not always enough. Add baking soda to the water and mix it into the consistency of a paste to handle tougher stains. Again, wipe with the grain of the finish.
Method 3: for oily fingerprint marks, glass cleaner can dissolve the grease. Surprisingly, the oil found in fingerprints can discolour a stainless steel finish. Try to do this once a day, preferably at the close of business to prevent permanent build-up or damage to the stainless steel finish.
Always remember to rinse or wipe over the surface with a chemical and soap-free damp cloth to ensure any residue from the cleaning products don’t cause long term damage.
Water spots will accumulate on the stainless steel surface, so drying the stainless steel surface after cleaning is imperative.
There are also a number of stainless steel specific polishes on the market which can assist in maintaining your stainless steel as well as the appearance of it. Always make sure you test the product in an inconspicuous spot and follow manufacturer’s directions.
Common stainless steel problems and their solutions
To cover more specific cleaning problems with stainless steel, use our table below.
Hard water (lime deposits) stains
Mix a solution of vinegar and water, at a ratio of 1:3. Soak if possible, then brush to loosen, rinse thoroughly.
Rust or corrosion
Light rusting can be shifted with nitric acid (10% concentration). Heavier rusting may require pickling – stripping of the impurities. The latter should not be attempted by an individual but by a licenced and certified company.
Remove as much of the charred leftovers with hot water and detergent. Clean and polish as required with a mildly abrasive pad – plastic or sponge only.
Use a nylon pad and use a polishing wheel for deeper scratches. Never use steel wool as this can leave iron deposits embedded in the scratches and cause further damage to the exposed stainless steel.
What to avoid
Have a close look at the cleaning agent in any store-bought solutions. Some may contain abrasive agents or acids that may affect the finish of your stainless steel. There are many commercial cleaning solutions that will be much better suited to maintaining the stainless steel surfaces of your appliance or equipment.
Steer clear of:
- Steel wool or other abrasive scouring pads – these will expose the stainless steel “protective layer” and enable corrosion to form
- Concentrated hydrochloric acids – hydrochloric acids are used to STRIP out impurities (such as the purposely added alloys to the stainless steel mixture) leaving the surface vulnerable to corrosion once again.
- Commercial kitchens often use heavy duty caustic based grill and oven cleaners. Steer clear of these where possible and if you do use the wrong cleaner, be sure to wipe the surfaces with clean water and some white vinegar to neutralise any acids.
Ask if you’re unsure
Many stainless steel manufacturers supply cleaning and maintenance instructions on how to care for your new appliance or equipment without damaging it in the process. If the instructions seem unclear or incomplete, cease cleaning the appliance/equipment and consult your supplier immediately. If any damage occurs due to incorrect cleaning of the stainless steel, it will not be covered under warranty for the product.