What the scientific explanation as to why you are not supposed to put kitchen knives in a dishwasher? how is this any different than hand washing them?
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One belief is that the heat in the dishwasher is hot enough to affect the temper of the blade making it more difficult for them to hold a sharp edge.
Rust.
High quality knives are made of a different kind of steel than flatware. In order to hold thinner sharper points, and to be able to handle sharpening, they are made from steel with less chromium and no surface coating — which protects from rusting.
Hot water over time will release free oxygen (unlike O2 which is in the air) which will lead to faster rusting.
The main reason is that your knife should only be wet for the minute or so it takes to clean it, then it should be dried. Having water sitting on there will make it rust and damage whatever finish it might have. Dishwashing tablets often have more salts in them compared to dish washing liquid which can eat away at metal. If your knife has a handle made from a separate material water can seep in the joints and corrode the glue or screws, which will be made of far cheaper metal than the blade.
Dishwashers will also jostle a knife around and the sharp edge can be chipped easily, and some people say the heat is high enough to warp a temper but I think that’s a pop cultural myth thing.
Dishwashers can damage the handles that are different materials, so expand/contract differently than the knife. And the blades can slide the rubber coating on the dishwasher racks, causing rust inside the dishwasher. Those are in addition to the potential damage to the blade knocking g around, excessive moisture exposure leading to rust on blade.
Dish washers are hostile environments, and only tough materials that can withstand it should go in there. Pots, pans, plates, glass, etc. Plastics are iffy – I, for one, have melted my fair share. Delicate things get damaged – wood, wood spoons, wood handles, wood cutting boards, anything wood glue that holds cutting boards and things together, and your knife edge.
Just a quick bit about wood – you can buy a bag of wood spoons for $10, and stick them in the dish washer, who cares? But wood you can’t cheaply and easily replace – cutting boards, utensil handles, rolling pins, DO NOT dish wash them. What you want to do is hand wash those things and then wipe them down with butcher block oil. Water is bad for wood, soapy water doubly so. There are oils in the wood that give it its shine and protects it, and you’re stripping it away. That’s why brown and blonde woods go gray, shrink, twist, and crack. Hot, soapy water is terrible for wood glues, too, and will take your cutting boards apart. Any wood finish on a bowl or nice spoon will dissolve, too.
If you have a stainless steel knife with a resin handle, it’s basically fine. Your flatware is all a cheap grade of stainless that can withstand the same environment. The biggest problem is that knife edge. Being battered around by, or battered by not only the water, but what’s in the water, can dull the blade.
We’re not talking butter knives, maybe steak knives, but definitely kitchen knives. If you want to keep that edge for as long as possible, you’ll hand wash that knife, and hone it before EVERY use (that long metal rod thing in the knife block). You can feel a dull knife, you can SEE a dull knife, when you look on edge and see chips and shine. An edge should look dull.
You can sharpen at home, and there are a number of emery board gadgets to help you upkeep your edge, you can even stone your edge yourself; but it takes practice, time, and patience. I recommend having your knives sharpened on whatever schedule makes sense for you, depending on how much you use them – every 6 months if you don’t know any better. A professional will be much faster and put a superior edge on it because they have the setup and the experience. It’s not expensive, and if you live in a city, you might even see a sharpener cart walking down your sidewalk, just run out and stop him.
Its because if u got knives pointing up in the wash basket thingy and you trip on the drop down door you might end up wearing the knife in you.
I think
You also run the risk of someone not knowing the knife is in the dishwasher…. and they get stabbed/cut.
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