Wash your knives in cold water

According to Jamie Oliver in his excellent 20-minute meals iPhone App, you need to wash your kitchen knives in cold water, or the edge will go dull.

That's news to me. I've always washed them in the warmest water possible, because I thought it was important to get them clean.

Not so, it seems.

I have a 28-layered Santoku knife from Tojiro-Pro, which I've had trouble keeping sharp.

I found out at some point that I was using the steel at a wrong angle (the edges of Japanese knives are at a different angle than European ones), but that hasn't done the trick. (And yes, I did have it sharpened after learning that, but it's gone dull again.)

Btw, I love the pattern on these knives.



Hmmm, I haven't seen that before. Does he have any details on how hot water damages the edge?
By Dave Bauer on Thu, Aug 12, 10 at 12:51 · Reply
Yes, he does. He say it's because the changes in temperature messes with the fragile edge.
By Lars Pind on Thu, Aug 12, 10 at 12:55 · Reply
Most of the tips seem sensible, but I'm very skeptical about the cold vs. hot water claim. Here's an article about tempering blades: http://www.balisongcollector.com/rockwell.html The relevant part is at the very end: "Knife owners are often quite concerned about heating their blades fearing that they'll somehow destroy the heat treatment. And it's true; you can un-harden steel -- "detemper it" is the common term -- by exposing it to high temperatures. To do that, you have to heat the steel to a temperature above the final heat-treatment temperature... The lowest final heat-treatment temperature in common use today is over 300F (177C). Leaving the knife on the dashboard of your car even on a very hot day will not detemper it. Sterilization by boiling will not detemper it. Even running it through a dishwasher won't detemper a blade. But putting it into a fire very well might." (Note that putting your knives in the dishwasher is still a bad idea, but that's because the handles shouldn't be wet for extended periods and because contact with other items can dull or chip the blade.)
By Kevin Scaldeferri on Thu, Aug 12, 10 at 14:04 · Reply
Here's what he's saying, verbatim: "Also, when you're washing the knife, try and avoid using hot water. Hot water will soften the metal and it'll take the edge off of it, so try and use cold water and a little detergent, and that's more than what you want. And only put them in your dishwasher if you're a raving idiot, because that'll screw up the handles, but, you know, my wife does it quite a lot, so we get through quite a lot of knives, but there you go. Try not to." So I guess he's saying both that the metal will go soft and the edge will blunt. //Lars
By Lars Pind on Thu, Aug 12, 10 at 14:09 · Reply
The problem w/ knives and dishwashers is that the long exposure to water and detergent will blunt the edge of the knife. The temperature in the dishwasher isn't the problem, but the detergent is. //Umahro
Interesting. So no problem washing your knives in hot water, then. I guess you're going to have to come over some day and show me what I'm doing wrong with my Tojiro. :)
By Lars Pind on Wed, Aug 18, 10 at 15:20 · Reply

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