Things you should avoid putting in dishwasher

The dishwasher is the workhorse of the kitchen. Dishes go in dirty and come out clean — day after day. 

How Dishwashers Work

First, water is heated and put through a series of sprayers to blast bits and pieces of food off of your dishes. It is helped in this process by the dishwasher detergent you use, which helps remove grease and has a sanitizing effect. Then, more hot water (between 130 to 170 degrees F, or 55 to 77 degree C) is sprayed at force to rinse, removing all traces of detergent to ensure your dishes are safe to eat off of. And finally, the whole unit may heat up extra hot to dry everything off. If you choose to use a rinse aid, this can help prevent water spots and is an extra boost to the cleaning process.

What are the things we should avoid putting in the dishwasher?

1. Sharp knives

Most good-quality cutlery has been heat-treated and tempered during the manufacturing process, creating the optimal hardness of the blade, and the super high heat in a dishwasher over time can alter this tempering, leading to the steel softening and making it more difficult to keep and resharpen the edge. And the dishwasher's heat and aggressive detergents can affect the handle of the knife, leading to damage over time. The knives can also bump up against other cutlery during the washing process, which can dull or even chip them or damage your other cutlery.

Source: Maria Siriano

Even if the manufacturer's instructions says it's OK to put knives in the dishwasher, you may cut yourself loading and unloading sharp knives, so the safest bet is to hand wash sharp knives.

2. Hollow-handled knives

Source: ASG.

Hollow-handled knives are those with blade and handle made of 2 different materials, and its handle is hollow and lightweight in the hands. High temperatures in the dishwasher can melt the adhesive that holds the two pieces of a hollow handled knife together. If that happens, the knife handle will fall apart. Hand wash to keep these in top shape.

3. Nonstick pots and pans

Unless the manufacturer specifically states that an item is dishwasher safe, do not put cookware with a nonstick coating in the dishwasher. Over time, the dishwashing process can break down the coating, causing it to flake off during cooking and ruining the nonstick finish.

Source: Better Homes and Gardens.

Nonstick pans are mainly composed of aluminum but the outer covering is done by a compound named polytetrafluorethylene (PTFE). PTFE, a plastic polymer has a long chain of carbon in the inside. Fluorine is attached with greater force on the outer side of this long chain. This PTFE likes to adhere with itself but does not like to attach with something else. 

Most detergents work by combining an alkali and bleach with a surfactant. Bleach will try to deteriorate the bond where the long chains of PTFE are already loosening, such as artificial scratches or scratches from metal utensils. The alkali will give 1 Hydrogen to the surface area of the nonstick pan which does not hurt the nonstick pan but might lead to sticking problem of food in the next use.

Often cheap nonstick pans have poor cohesion between the pan and the coating. The surfactant depending on the cohesion power of your pan and due its composition may treat PTFE as it is a food item which is stuck to the pan. Hence this might lead to loosening of the bond that holds the PTFE which results in microcracks in the pan. Finally, this might lead to the detachment of the coating.

4. Cast iron

Cast iron should NEVER go in the dishwasher. It takes a long time to build up a nonstick surface on cast iron and dishwashing detergents will strip it away and leave the pan vulnerable to rust. Plain water and nonabrasive sponges are the best cleaners. Take care of cast iron cookware and it can last for many generations.

5. China dishware with metallic decoration

Source: Otantik Imports.

Surprisingly, most porcelain and china dishware is dishwasher safe. But if your dinnerware has metallic images or trim, hand wash it to prevent damage to the decorations. The heat from the dishwasher may tarnish or remove the metal detailing. 

6. Antiques and other delicate items

Delicate items such as hand-blown glass, antiques and fine figurines should stay out of the dishwasher. The color and detailed patterns from vintage and antique pieces can get faded in the dishwasher. 

Source: Etsy.

Actually, you should keep antique glassware out of direct sunlight and avoid extreme weather conditions and temperature changes in the storage area. Don’t place glassware in area where vents will blown hot or cold air directly on the items. Allow items to assume a normal room temperature before relocating to another area, as drastic temperature changes may cause glassware to crack.

7. Hand-painted ceramics and stoneware

Unless you want the artwork to go down the drain over time, you should hand wash these items.

8. Crystal

Some lead crystal will etch (become cloudy and pitted) after repeated washings. Always follow the manufacturer’s instructions to be safe.

9. Milk glass

Source: glass bottle marks

Pop semi-opaque milk glass dishware in the dishwasher too many times and that milky white color can turn yellow. Don’t take a chance. Hand wash these items.

10. Gold-colored flatware

Source: Food and Wine.

Unlike silver, most of which can go in the dishwasher, gold-colored flatware will discolor in the dishwasher.

11. Pressure cooker lids

Source: Detoxinista.

Never wash pressure cooker lids (including those for stovetop pressure cookers and those for electric types, like the Instant Pot) in the dishwasher as small food particles or dishwasher detergent can collect or lodge in the regulator or safety valves. Instead, wash pressure cooker tops, gaskets and pots by hand in warm, soapy water. Rinse and dry well. Do not store with the top in place as the gasket may seal permanently and you may lose the pot.

12. Brass, bronze or pewter

These metals can become pitted and discolored when washed in the dishwasher. Hand wash to maintain their beauty.

13. Aluminum cookware

Source: The Times of India.

The very hot water in dishwashers can stain the surface of aluminum and harsh dishwasher detergents can dull the finish. Even if you don’t care about damaging the looks of flimsy disposable aluminum pie pans, don’t put them in the dishwasher because they can mark nearby items as they move around during the washing cycle. On the other hand, some stainless steel cookware can go in the dishwasher — be sure to check the manufacturer's instructions and rinse the pots and pans well if you are not planning to run the diswasher immediately.

14. Wood

Very hot water can warp or crack the wood and damage the finish on wooden cutting boards and utensils with wooden handles. Deformities tend to appear on wood when the moisture content is

changed unevenly in several parts of the wood. Therefore, anything that is wooden should be hand washed and left to air dry if at all possible. A few drops of water won’t hurt as long as it dries quickly, but a dishwasher would drench the wood for over an hour, causing warping to form. 

Source: Indigo True.

If you have ever had a floor that is wooden, you might be very familiar with warping. When unwanted moisture enters the floor, it tends to lift and separate. That can become very frustrating. That is essentially what happens when wooden cutting boards are washed.

You can put your cutting board in the dishwasher if it is made from thick plastic or glass and labeled dishwasher safe. However, cutting boards made from thin plastic, wood, metal, or other materials, like granite, should not be put in the dishwasher.

There are also bamboo cutting boards that are usually grouped in with wooden cutting boards, but bamboo actually isn’t wood despite the visual similarities. However, those similarities do not translate in other ways.

Though bamboo still isn’t recommended for dishwashers, it actually will retain its shape and will not soak in water like wood keeping it from warping. The issue with bamboo and dishwashers actually lies in the excessive heat.

If you’re interested in less maintenance with bamboo cutting boards, you might want to consider buying one instead of wooden cutting boards. You won’t have to deal with any warping or cracking keeping you from worrying too much about using mineral oil or beeswax to maintain the cutting board’s shape.

15. Many types of plastic

Unless they're marked “dishwasher safe,” do not put plastic items in the dishwasher. Items that are labeled “dishwasher safe” should be placed on the top rack only. Otherwise, the heating element may melt or warp them.

16. Insulated pitchers, drinkware and travel mugs

Source: The Spruce Eats.

Unlike standard cups or tumblers, an insulated cup has two layers: an inner wall and an outer one, separated by air that creates a vacuum. This vacuum and the seal that ensures it is what keeps your cold beverages cold (even on very hot days) and your hot beverages hot (even when you're shivering on a cold car seat). Most likely, the manufacturer of your favorite insulated cup has placed the words "hand wash only" on the label or bottom of the cup itself and not "dishwasher safe." This means cleaning it with warm, soapy water in the sink and allowing it to dry is the only way to go.

Handwashing is especially important with these items as the heat of the dishwasher can (and likely would) damage the ever-important seals on the cup, allowing air into that precious insulated airspace and compromising its ability to keep that which is cool, cool or hot, hot. In addition, the dishwasher's heat can cause cracks in the walls, allowing hot water in between them, where it gets trapped and sloshes around in an annoying fashion, broadcasting the cup's untimely ruin with every step you take.

Not to mention, depending on its composition, the plastic may simply flatten or warp.

17. Acrylic dishware

Source: West Elm.

Acrylic is molded plastic with great clarity and transparency, and is a good substitute for glass, as it is shatterproof. However, Acrylic will crack or break if dropped! Acrylic glassware will not yellow, and the colors are weather and sunlight resistant; acrylic drinkware resists most chemicals found in normal use. The very hot water and harsh dishwashing products can damage acrylic plates and other dishware, causing hairline cracks and washing away whatever is imprinted on them. Hand wash such items to keep them looking new.

18. Plates you've glued back together

If you've repaired a dish with glue or some other type of adhesive, wash it by hand. The hot water and harsh detergent used in the dishwasher can dissolve adhesives.

19. Printed measuring cups

Source: The Low Vision Store.

Measuring cups with measurements printed on the side are best hand washed. Over time, dishwasher detergent will remove measurements on these cups, rendering them useless for measuring.

20. Anything with paper labels

Dishwashers can loosen and remove paper labels from bottles and jars. These pieces of paper can lodge in the drain of the dishwasher or stick on other dishes, creating a messy clean up problem. Remove labels first.

Source:

https://www.today.com/food/21-things-you-should-never-put-dishwasher-t108971

https://www.eatingwell.com/article/8071957/knives-in-dishwasher/

https://dishwashingpro.com/can-you-put-nonstick-pan-in-dishwasher/

https://www.woodcuttingboardstore.com/can-i-put-my-cutting-board-in-the-dishwasher/#:~:text=You%20can%20put%20your%20cutting,be%20put%20in%20the%20dishwasher.

https://www.allrecipes.com/article/are-insulated-cups-dishwasher-safe/