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Science of hot foods ruining knife temper?

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Tristan

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I remember reading that one should designate a slicer to be used for hot foods (e.g. roasts, carving) as the ongoing heat could affect the knife's temper in some way or form.

Is there science behind this or is this actually a concern? What knives are heat treated to overcome this issue if it exists?

Thanks!
 

MadMel

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Seriously??
I don't really thing the food will get that hot to begin with!! A well done steak only has an internal temp of 75 celcius which I think is wayyy lower then the tempering temp??

Correct me if I'm wronG!!
 

Candlejack

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Hahaha, this is even better than the knife-lecture i got from my teacher..
 

ajhuff

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I'm willing to bet that what most mean by "ruined/lost temper" is annealed and that knives that actually have their tempering altered is rather rare.

-AJ
 

Tristan

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Thanks, so I guess there is no truth to worrying about the knife and hot foods then. Be careful what you read and a little knowledge and all that.

There was also something (perhaps I remember badly) about boiling hot water and carbon steels and the blades reacting to that or something (I may have remembered Dr Naka).

Might as well ask, since it is along the same lines of heat and kitchen knives.
 

tk59

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I hope you didn't read that in a reputable publication.

The Dr. Naka thing was about pre-treating your knives, forming a thin layer of non-reactive material to reduce stinking and discoloring of foods with carbon knives. I haven't really seen it work to an extent where I'm absolutely certain it isn't my imagination.
 

Lefty

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I'm in the same boat as Tk. I still rinse my knives with next to boiling water, just in case. So far, I've had zero issues since doing so.
 

JasonD

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This is the first I've heard of the boiling water rinse thing. How is it supposed to go? You just splash the blade with hot water before using it and it's supposed to help prevent the reaction with the food?
 

Don Nguyen

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I've heard/read from a lot of places not to get the knife too hot, ex. putting in dishwasher. Though, the reason that you don't put a knife in the dishwasher isn't the heat; it doesn't get anywhere close to hot enough.

Honestly, besides deep frying or baking a knife on accident, I don't think it can tinker with the temper at all.
 

Pensacola Tiger

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Over on the razor forums, the same stale urban myth about ruining a razor with boiling hot water comes back over and over.

If it were anywhere near true, autoclaves would never have been invented.

Rick
 

JohnnyChance

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If you are looking for an excuse to buy another slicer....then yes. You need AT LEAST two, one for hot items and one for cold.
 

eshua

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As to the 500F, does this mean i can curse out my cooks when i see them heating my knives over a burner to cut foie gras for sashimi?
 

Eamon Burke

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When it starts to turn blue, you should just put it in one of the cooks.
 

David Metzger

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Heat treat tempering can be as low as 300 degrees F. As the tempering temperatures goes up the hardness will typically go down. I would guess that most carbon knives for kitchen use that are high end are tempered around 400 degrees. Stainless usually has higher tempering temps but not always. Each steel has a different recipe for tempering and what RC hardness that will create. It is more complex than that but "don't heat it over 325F".

I have not experimented enough, but the very edge of your edge in theory loses some of its temper if you use dry stones, dry sandpaper, etc to sharpen.

David
 

Eamon Burke

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I have not experimented enough, but the very edge of your edge in theory loses some of its temper if you use dry stones, dry sandpaper, etc to sharpen.
Put the tip of a paring knife on a 120 grit AlOx belt for about 4 seconds. Temper = Blown. :slaphead:
 

ajhuff

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Please. Tell me more, be more descriptive.

Thanks,

-AJ
 

Justin0505

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As for the hot water patina thing, the way that I always thought about it was that heat speeds chemical reactions such as oxidation. What seems to speed the process is the water heating the blade, not just the water its self.
I've used a process that goes like this:
-heat blade in hot water
-cut reactive food (I like raw beef)
-while blade is still warm, wipe blade w/fingers so there is just thin layer of reactive residue.
-rinse / heat again under hot water
-dry, observe
-repeat


I've tested this with warm water, cold water, and no water(other than the final rinse). The hot water method clearly forms a patina the fastest; you can actually see it form with your own eyes.

Oh yeah, as to the OP, I've never noticed any ill effects(to my knives) from all the hot water exposure.
 

Eamon Burke

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And so what happened? Did the tip become dead soft?

-AJ

Well it didn't turn to putty. But yeah, it became incredibly weak. Forming an edge was so difficult, and it failed on first contact, I just ground the tip right off. Luckily it was a sharpening-practice knife, I was learning to use my HF belt sander to sharpen and hadn't bought real belts yet.
 

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