Stop Putting These Things in the Dishwasher
The dishwasher can clean many things, but there's still a lot you shouldn't load into it, from blades to wooden items and items made of reactive metal.
Serious Eats / Vicky Wasik
I'm the dishwasher-loader in my family, not because I want to be, but because I have to be. I think a convincing case can be made that observing a person load a dishwasher is the quickest way to understand how their brain works. Or, doesn't work, as the case may be.
Take my wife, Kate. She's brilliant, but her brain doesn't do efficiencies and logistics. I know this because every time I open a dishwasher she's loaded, I marvel at the bizarre arrangement, mystified by a use of space that seems designed to set off my OCD. How have five glasses managed to take up the entire top rack? Why are those two bowls nested so that the upper one is still dirty? And—god damn it—I said not to put anything aluminum in there!
I hold up the offending item, "C'mon, I said no aluminum!" She looks at me sheepishly, but there's a gleam in her eye that tells me she's enjoying this. "Sorry," she says as the corners of her mouth fight off a grin, "I forgot."
I can't help her, but I can help you, at least in terms of what you should, or, really, shouldn't, be putting in there. How do I know? Well, my brain just works this way. (And maybe, just maybe, I've made enough of my own mistakes over the years to learn the hard way...but shhh, don't tell my wife.)
Knives, Blades, and Sharp-Edged Tools
Serious Eats / Liz Clayman
Examples:
Chef's knives, santoku knives, paring knives, slicing knives, serrated knives, and more.
Food processor blades.
Blender blades.
Mandolines and handheld slicers.
I know the temptation. You've been cooking dinner all night; all you want to do is go flop on your bed and scroll mindlessly through Instagram, but you've got a mountain of dishes to get through first. In these moments, even the smallest cleaning task can feel deeply undesirable.
And that's how you find yourself looking at your dirty knives thinking, it wouldn't be too bad if I popped these in just this once, right?
But it is bad, for several reasons.
The first is safety. You may be the one to load the dishwasher, but you may not be the one to unload it, and unsuspecting hands rummaging through a tightly packed dishwasher are bound to find those blades, sometimes from the wrong end. No matter how careful you think you've been, sharp objects in the dishwasher remain a danger (they're equally dangerous tossed into an overflowing sink of dishes). For safety's sake, you need to hand-wash any and all knives and blades, except the dullest ones, like butter knives.
On top of the laceration risk, putting your blades in the dishwasher is terrible for the knives themselves. The strong detergents will more rapidly dull their sharp edges, which is particularly bad for home cooks who don't sharpen their knives frequently. Handles can be damaged, too, and metals (especially carbon steel) can rust.
In case that's not enough to convince you, keep in mind that blades can also damage your dishwasher, digging into the rubberized coating on the dishwashing racks, which can lead to them rusting down the road.
Pretty Much Any Metal Except Stainless Steel
Serious Eats / Liz Clayman
Examples:
Copper pots, pans, and utensils.
Aluminum cookware, baking sheets, and utensils (e.g., old-school ice-cream scoops).
This is a lot of stuff, so the easier way to think of it is this way: The only metal you should ever consider putting in your dishwasher is fully stainless-steel stuff that won't easily be damaged or rust (even then, rust is still possible). Cast iron or carbon steel will have those layers of seasoning you carefully built up stripped off, and then will rapidly rust in the humid environment on top of that. You should also avoid putting enameled cast iron in the dishwasher; the metal is mostly protected, but the enameled finish can still be damaged.
Aluminum doesn't belong in the dishwasher, either. Not too long ago I bought a bunch of vintage aluminum steakhouse sizzle platters off eBay, then mindlessly loaded them into my dishwasher. What came out was dull and blackened, with cloudy white dry patches. Aluminum, as I should have remembered, is highly reactive. To deal with this, manufacturers often anodize it, meaning they coat it in a protective oxide layer that won't react with other substances. The problem is that phosphate-based dishwasher detergents can neutralize this anodized coating, allowing the metal to get all funky. It's not a deadly mistake—you can still use aluminum that you've harmed in this way (at least, I didn't find any compelling evidence that it's harmful, though you may want to be more cautious than me)—but it's unsightly and, over time, not good for the durability of the equipment.
Serious Eats / Liz Clayman
Tarnish-prone metals like copper and brass are also best left out of the dishwasher, since they can lose their luster (and eventually take on damage) under the onslaught of those harsh detergents.
And nonstick cookware? Forget it, that delicate coating will break down even faster if you run it through the dishwasher. (And why would you dishwash a nonstick pan anyway? It's the easiest surface to clean of them all, a quick wipe is all it takes...and if it doesn't, you probably need a new nonstick pan.)
Fragile Plates, Delicate Glassware, Fine China
Serious Eats / Liz Clayman
Examples:
Fine china.
Gilded and hand-painted plates.
Printed measuring cups.
Milk and uranium glass.
Delicate crystal and stemware.
Confession: I often put my wine glasses, including crystal, in my dishwasher at home, and I've never had a problem. Then one time I was visiting my mother-in-law, and after dinner one night I insisted I could do the same with all her fine stemware. "Don't worry," I implored her, "It'll be fine, these things are designed to wash this stuff without it breaking, I do it all the time." I think you know where this story ends up. I still apologize for it when I visit.
Any fine china, pottery, and glassware that's valuable or delicate is better off staying out of the dishwasher, unless you're willing to shoulder the risk that you'll ruin or break it. And just to be clear, the trouble goes beyond just shattering your stuff. Hand-painted designs on plates and printed measuring lines on glass measuring cups can wear away over time, and crystal and glass can grow cloudy and discolored.
I still often put glass measuring cups in the dishwasher, but I do it with the understanding that after several years the markings may fade and it'll be time to buy new ones. I've accepted that risk. Calculate yours before you accidentally ruin the things you own.
Anything Wood
Serious Eats / Liz Clayman
Examples:
Wooden spoons, spatulas, and other utensils.
Wooden salad bowls.
I always thought this one was incredibly obvious—wood is an organic material that can be damaged by moisture and heat. It absorbs water, swells, warps, and cracks. And yet I've pulled wooden spoons and other tools from more dishwashers than I can count. I don't get it. I mean, I know people used to wear wooden dentures, but you know why we don't anymore? Because saliva-saturated teeth are freaking disgusting, and dirty dishwasher water–logged cooking tools aren't far behind.
Anything Mechanical
Serious Eats / Liz Clayman
Examples:
Once upon a time, there was a Tin Woodman who got caught in the rain, and froze right on the spot with his joints rusted solid. The story is a long one and has many morals—we all have heart and smarts and courage if only we believe in ourselves; don't lie; there's no place like home—but those are trivial compared to the big lesson this story offers: Don't put mechanical stuff in the dishwasher if you want it to keep working.
If it has gears, cranks, moving parts, or valves, clean it by hand following the manufacturer's instructions.
Natural Stone (Marble, Granite, etc.)
Serious Eats / Liz Clayman
Examples:
Granite mortars and pestles.
Marble, slate, and other stone surfaces.
Stone is a lot more durable than wood, but it's still better left out of the dishwasher. Detergents can harm the finish, and exposure to high heat and lots of water can take its toll, and even cause fractures and cracks.
Some Plastics
Serious Eats / Liz Clayman
Examples:
Plastic cutting boards.
Plastic storage containers.
This is a group I'm less emphatic about, but it's worth thinking about in your own home. There are a growing number of voices that have issued statements and guidelines expressing concerns that many of the plastics in our lives may present some health risks, especially to children. In part, the worry is around dishwashing and microwaving those plastics, which may degrade through repeated heating and washing cycles.
I have to emphasize, this is not at all settled science, and there are plenty of people out there who would pooh-pooh those concerns as alarmist and unsubstantiated. But, in the absence of conclusive evidence, it may still be worth reducing the amount of plastic we run through the dishwasher repeatedly. There's certainly little harm in that, especially when there are plenty of glass, wood, and stainless steel storage options out there to use instead (though, as mentioned above, the wood should stay out of the dishwasher as well).
On a more practical level, some plastic items can be damaged in the high heat of a dishwasher. Over the years I've put more than one plastic cutting board that claimed to be dishwasher-safe in the dishwasher, only to find it warped when it came out. Some people claim that putting those plastic boards on the top rack only will prevent warping from happening, but...why risk it? (And, also, how useful is that advice anyway, given that only the smallest cutting boards will fit on the top rack?)
Anything With a Hollow Handle or Thermal Insulation
Examples:
Silver knives.
Some pots.
Old-fashioned ice cream scoops.
Travel coffee mugs, Thermos bottles, and other insulated containers.
I once nearly killed myself with an exploding stainless-steel sauté pan. It had a commercial build with a hollow, tubular handle that was welded on one end onto the pan body, while the other end had been crimped shut under the force of a powerful press. I used to put that pan in the dishwasher regularly, assuming the stainless steel could handle it.
Turned out the stainless steel could but that sealed hollow handle couldn't. I found this out the hard way one night while heating the empty skillet on the stove top to make dinner. I got a phone call, which distracted me for a few minutes until an ear-drum-shattering explosion rocked my kitchen, the pan flipping up into the air and crashing on the floor while a projectile shot across the room and cracking into the backsplash by the sink.
What I realized after was that all those dishwashing cycles had allowed moisture to penetrate the seal on the crimped end of the tubular handle. Eventually enough water had accumulated in it that, when heated, enough steam built up to blow the crimped end open.
This was an extreme case, but it's a good reminder: water has a way of working its way into spaces it's not meant to go, and in a dishwasher, that's often into the sealed hollow handle of utensils like whisks and sterling silver knives, and inside the vacuum walls of thermal bottles and coffee mugs.
Those things may never explode on you the way my pan did, but that water will still take its toll, at the very least growing moldy or rusty, or worse significantly crippling the ability of the hollow space to act as a thermal barrier.
Crazy Stuff (Seriously, What the Hell Are People Thinking?)
Examples:
Bras.
Engine parts.
Computer keyboards.
I can't believe I'm typing this, but apparently all of the above are things some people think are a good idea to put in a dishwasher.
Nah, you know what? I'm not even going to say not to do that stuff. If you do and it breaks your dishwasher, you deserved it. But if it works? Well, you're a genius.