So you dropped a few hundred or more on that stainless steel cutlery set – do you really want to risk cleaning it in the dishwasher? Will it survive the wash? And if it says dishwasher-safe, why do you still get rust spots on some knife blades?
This guide explains just how stainless stainless steel is, and helps you understand how you can get the most out of your new investment.
What is stainless steel?
'Stainless steel' is steel that's had chrome added to it for rust resistance and often nickel for acid resistance.
High-quality stainless steel (18/10) contains 18% chrome and 10% nickel. It's generally more expensive – and brighter and whiter in colour – than lower grade 13/0 stainless steel, which can look quite grey.
In short, yes, though to a much lesser degree than mild steel. Despite its name, most metal alloys used in cutlery make it stain-resistant rather than stainless.
When the surface of normal steel is exposed to oxygen, it usually forms ferric oxide (Fe2O3) which has the well-known red rust colour. Ferric oxide doesn't form a continuous layer on the steel because the oxide molecule has a larger volume than the underlying iron atoms, and eventually spalls off leaving fresh steel exposed and prone to further corrosion.
Because of the high chromium content of stainless steel, a thin layer (a couple of atoms thick) of chromium oxide forms on the surface, not ferric oxide, because chromium has a strong attraction to oxygen. Unlike ferric oxide, this layer doesn't spall off, and acts as a protective barrier between the stainless steel and the air, preventing further oxidisation.
So in short it's the chromium in stainless steel that protects it from rusting, and the higher the levels of chromium present, the better the resistance to oxidisation.
Damaging chemicals, salts, grease, moisture and heat for prolonged periods of time, all of which are present inside your dishwasher, can cause pitting and corrosion on stainless steel.
Heat and moisture aside, another big cause of corrosion in the dishwasher is the detergent: a highly alkaline mixture of several different salts. Strong chlorides such as dishwasher detergent can greatly accelerate pitting and oxidisation in much the same way that salt water does in marine stainless steel applications.
While most forks and spoons have excellent corrosion resistance, all stainless steel cutlery is not created equal – your knives tend to be made of harder steel that gives a lasting edge but is more likely to rust, eventually, from repeated washing in a dishwasher. That's why corrosion is largely the providence of the knife, not the fork or spoon.
- Acidic and salty food remnants on cutlery will stain it. Take care to scrape salty solids from your cutlery before loading in to the dishwasher, and while we advise not to pre-rinse, if you're not running your dishwasher for a while then your cutlery may be an exception to the rule.
- Don't store dirty cutlery in your dishwasher for days before washing – this will stain it eventually.
- Don't leave wet cutlery in the dishwasher for long periods after the cycle has finished – take it out as soon as possible and dry it off, or at the very least open the door to assist in drying.
- Over-packing the cutlery basket means staining. Use an anti-nesting grid in your cutlery basket, or a cutlery tray if you have one, so items don't touch each other. It's important that stainless steel and silver-plated or copper items don't come into contact, as the chemical reaction with hot water and dishwashing detergent can cause discolouration.
- Don't pour dishwasher detergent directly onto cutlery – it's highly alkaline and stainless steel can pit within minutes. Silver-plated cutlery can also become permanently stained.
- Don't soak cutlery for long periods in soapy water, bleach solutions, or salt water.
- Don't use abrasive cleaning aids.
No. The high carbon content of good quality chef's knives is particularly susceptible to corrosion in the inhospitable environment inside a dishwasher, and you also risk dulling sharp edges as your knives rattle around and bump into each other.
Stainless steel aside, there's plenty of things that can't go in the dishwasher at all, such as bone-handled cutlery, or anything else that pre-dates the invention of the dishwasher for that matter.
It's also a safety risk, and you could give yourself a nasty cut reaching into a dishwasher without due care and attention or worse, losing your balance and falling into it.
Experts generally recommend skipping the dishwasher and washing and drying good quality chef's knives by hand.
While inhaling large amounts of rust can cause respiratory issues, this isn't likely to be an issue at the dining table and while it's not ideal, ingesting small amounts of rust from your cutlery won't hurt you (unless you suffer from hemochromatosis, a rare disease which causes your internal organs to retain iron). In fact, iron oxide is even routinely used as a food colouring.
In other words, a bit of oxidisation on your cutlery is perfectly safe, so long as the rust and oxidisation weren't caused by exposure to faeces or soil, which would mean they're likely covered with harmful bacteria. Even then it's the bacteria that's harmful, not the rust, and if you're eating with cutlery that's been buried in faeces you really need to rethink your life choices.
Stains such as water marks can generally be wiped off easily from your cutlery, and rubbing with a bit of lemon juice can help loosen oxidisation. But more persistent rust stains will need a cleaning compound (either a baking soda paste or a commercial cleaner) and a generous helping of elbow grease. If you're using a commercial compound make sure you choose a non-abrasive one formulated specifically for stainless steel, not a silver cleaner.
Rub your cleaning compound of choice into the rust spots using a plastic scourer until the rust is removed, then further buff it with a paper towel. Don't ever use a metal scourer – it'll strip more of the chrome from the alloy.
Once you've removed the rust stains from your cutlery it's time to polish it up to a mirror finish.
Switch the scourer for a soft cloth and grab either a commercial or natural (such as lemon oil) polishing compound. If you're using a commercial formulation, it pays to read the label and make sure you're using one that's suitable for use on eating utensils, and review any specific instructions for use.
Whatever you're using for polish, you'll generally need to pour some on your cloth and start to rub back and fourth on your cutlery, following the grain of the metal – like wood, stainless steel has a grain and polishing with the grain will give you superior results.
Once done, buff your cutlery clean and take a moment to admire your smug reflection staring back at you from your knives.
Stock images: Getty, unless otherwise stated.