What can and can't go in the dishwasher

Often kitchenware will come with a label or icon if they are dishwasher safe. But what if you can’t find any guidance? Or you've long forgotten what the tag said?

Liz Oldfield is the director of Auckland-based Milly's Kitchen, which has been in the business of kitchenware for 42 years. She says you have to consider whether you’re up for sacrificing some scuffs and marks for the convenience of a dishwasher.

“If you're somebody who really likes things to look brand new forever, then there are some things that you probably wouldn't put in the dishwasher that are dishwasher safe.”

Consumer NZ product test writer Erin Bennett recommends leaving out silver, fine china, crystal, wooden kitchenware like chopping boards, thermos and insulated flasks, cast iron, brass and copper items. All this is based on research, experience and testing, she says.

Under high heat and detergent, these items can tarnish, fade, chip and break, warp, rust or erode protective and non-stick layers over time, Bennett says.

“When it comes to things like the copper, which is just a discolouration issue, you just polish them back up and they're back to normal kind of thing. So they should be fine.

“[Wooden chopping boards], you can put them in the dishwasher, but you will need to expect them to warp and eventually crack … it's like giving it a limited lifespan essentially, because they need a good amount of time to dry out and the more humid environment of a closed-in dishwasher just makes that a harder process for them.

“So plastic [chopping boards] in theory should be fine as well. Again, if you see them start warping, then don't put them in. The thicker they are, the better they will deal with the dishwasher.”

Similarly, if there’s glue holding together different materials – like utensils with wooden or bone handles – this can fall off, she says.

If your items still have sticker labels, these can get stuck in the filter, Bennett warns.

For grill tools, stainless steel spatulas are fine, Oldfield says, but ones with carbon steel material and materials in a “raw state” (like cast iron) shouldn’t go in.

She also doesn’t recommend putting in knives because these can rust and the handles can be damaged.

Oldfield says most cutlery is 18/10 stainless steel (that is 18 percent chrome and 8 percent nickel and the strongest grade) so should be fine but items that aren’t 18/10 – which might be can openers and peelers – can rust and transfer that onto cutlery.

“You can put a microplane in, for example, but … that's one of the ones I think that you would sacrifice maybe some longevity for convenience in the short term.”

Non-stick cookware also won’t last as long if you keep chucking it through the dishwasher, she says.

Bennett says aluminium, non-stick cookware, lunchboxes and water bottles can be made with various materials, and some manufacturers claim their products are dishwasher safe. So it’s safer to check the label.

Plastic containers or plasticware can warp too, she says. “We've even heard of some that claim to be dishwasher safe, then ending up warping. It’s people saying that they used the normal wash, not like a particularly hot one.

“So you can use the Consumer Guarantee Act to go back and claim, say it wasn't fit for purpose - if it claims to be dishwasher safe and it turned out not to be.”

Some air fryers’ parts, such as the basket, may be dishwasher safe – again, it’s best to check what the manufacturer says.

The dishwasher's heating element is usually at the bottom, she says, so it’s best to place more fragile (like glassware) or sharp items and dishwasher-safe plastic plates at the top.