39 replies to this topic

[Fat Guy]

Mother-in-law just gave us a "watermelon knife" with a red nonstick coating on the blade. Could nonstick coatings on knives possibly be a good idea? Does anybody have any experience with them? Kuhn Rikon seems to make quite a few.

[Kim Shook]

My dad gave me a couple of the small (almost paring knife size) Kuhn Rikon non-stick knives. A regular blade and a serrated one. I don't see that it improves the knives performance, but it doesn't seem to impair it either. I actually use them a lot - they are a convenient size and sharp as hell. I've never sharpened them - haven't needed to - but I wonder if you are even supposed to with that coating.

[boilsover]

Sounds about like a skydiving anvil to me, FG. But the colors must be purty.

Theoretically, coating a blade with PTFE might make it transit the melon easier, as does a PTFE-coated bullet. Beyond that and color, I don't get it.

Would it be folly to ask MIL?

[Panaderia Canadiense]

I've seen them around here as well, but anything coated in PTFE gives me the screaming willies. Especially a knife, which I wouldn't be able to resist sharpening eventually. It also strikes me as a sort of gilded lilies thing - I've never had too much of a problem with anything sticking to my stainless and carbon steel knives, and I can't see the point in non-stick coating on a knife....

[scubadoo97]

With a convex edge they are all non-stick

[David Ross]

I'm not so sure I'd like the red color of the blade. Might mask things when I cut myself. Honestly, I prefer the silver sheen of a traditional knife as I can see better as the blade cuts against food of a different color...

[avaserfi]

I'm not sure I understand the purpose of such a coating. How would it actually help with any cutting tasks?

[Fat Guy]

Here by the way is a video from Kuhn Rikon promoting the watermelon knife.

[Dexter]

My brother had a similar knife (not the melon version) from Kuhn, and indeed, the PTFE started coming right off with the first sharpening. He told me that the knives were priced at a level, and performed essentially where they are essentially disposable.

[slkinsey]

There are any number of knives made for cutting sticky things that have various treatments to minimize surface adhesion (for example this "open blade" cheese knife). This is also part of the philosophy behind a Granton knife. A PTFE coating could be useful in this regard. Watermelons do have a tendency to stick to the sides of the blade, although I'd need to eat a lot of watermelon to want a dedicated watermelon knife.

[dcarch]

Do you remember Physics 101? You put two small flat pieces of glass with a drop of water in between. Due to atmospheric pressure, you will not be able to pull it apart.

What keeps food on the blade is mostly atmospheric pressure, not friction, therefore non-stick does not do much.

dcarch

[Fat Guy]

I'd need to eat a lot of watermelon to want a dedicated watermelon knife.

It so happens we do have a dedicated watermelon knife! We also eat an abnormal amount of watermelon. As watermelon season will soon be upon us, I'll be sure to report on the efficacy of this product.

[HowardLi]

Do you remember Physics 101? You put two small flat pieces of glass with a drop of water in between. Due to atmospheric pressure, you will not be able to pull it apart.

What keeps food on the blade is mostly atmospheric pressure, not friction, therefore non-stick does not do much.

dcarch

And without friction, even infinite pressure wouldn't stop food from sliding off.

Non-stick might not help melonage, but it certainly makes cleaning grease off the knife easier.

[Heartsurgeon]

i use a kuhn Rikon paring knife instead of a lame to slash my bread prior to baking. The non-stick works fabulous in this setting. Highly recommended for cutting "gooey" or sticky items, like wet dough.

[Ashen]

would this kind of coating help reduce browning when cutting things like lettuce??

I have a ceramic knife I use for things like that for just that reason.

[Norm Matthews]

Do you remember Physics 101? You put two small flat pieces of glass with a drop of water in between. Due to atmospheric pressure, you will not be able to pull it apart.

What keeps food on the blade is mostly atmospheric pressure, not friction, therefore non-stick does not do much.

dcarch

I don't see any analogy between sticking two pieces of glass together with a drop of water and slicing a watermelon. With the glass you are exerting a totally different pressure (up and down) than with the back and forth effort with a knife. Non stick has noting to do with it. serration does.

[Andreas]

I wondered about sharpening the knife. Since I use a waterstone to sharpen my knifes I would be a little bit concerned about coating e.g. that residues of the coating make the stone unusable. But after seeing the knife...this won't be a problem, you can't sharpen that knife that way anyhow... (+ I suppose you don't really need to sharpen that, especially as long as you only cut watermelons) But I would be concerned if it was a chef's knife, santoku, etc.

Regarding the lettuce: as far as I can remember, the lettuce is not browning because of the metal itself, but because the lettuce cells are damaged more then by ripping the lettuce apart (ripping causes the lettuce to mostly come apart at the cell walls). (Maybe that's why the ceramic knife is better in that regard ). I searched a little bit on the internet, but I could not find any reputable resources for this theory, so maybe just a food myth?

Edit: I just found a paper that suggests that browning is not different from cut to uncut lettuce. They not explicitly specify the material of the blade, just that it was a razor knife, which suggests that it was metal. Paper: Phenylalanine ammonia lyase inhibitors control browning of cut lettuce

Edited by Andreas, 28 March 2012 - 01:45 AM.

[Shalmanese]

I bought a bread knife with the coating a) because it was serrated so it was never going to be sharpened anyway and b) it was like, $4. I think they're great as essentially disposable, serrated knives, I wouldn't use one for any heavy duty tasks.

[rotuts]

I have a number of the Granton (GB) knives. You notice the edge effect with larger knives that are cutting thicker items.

There large, long slicer is a fantastic knife:

http://www.knifemerc...?productLine=32

so are the boning knives, but as they are thinner the edge might not matter as much.

I have a large 'Chef' knife, and in there catalog it does not have that edge, nor does the 'chinese' cleaver, but they put them on those knives for me at minimal charge and I use those all the time.

The Edge-Pro turns them into razors.

[dcarch]

Do you remember Physics 101? You put two small flat pieces of glass with a drop of water in between. Due to atmospheric pressure, you will not be able to pull it apart.

What keeps food on the blade is mostly atmospheric pressure, not friction, therefore non-stick does not do much.

dcarch

I don't see any analogy between sticking two pieces of glass together with a drop of water and slicing a watermelon. With the glass you are exerting a totally different pressure (up and down) than with the back and forth effort with a knife. Non stick has noting to do with it. serration does.

The original poster asks "Could nonstick coatings on knives possibly be a good idea?" and not just about watermelon cutting.

Food clinging to knife blades while cutting is very annoying. Kuhn Rikon and other makers of non-stick coated knives claim, “Nonstick coating keeps food from clinging to the blade” Which I think is not completely true.

Atmospheric pressure is what mostly keeping food adhere to the blade, that’s why you see knives with holes in the blade body and Granton edge flute designs on both sides of the blade (dimples). These features are to minimize atmospheric pressure.

dcarch

[weinoo]

There are any number of knives made for cutting sticky things that have various treatments to minimize surface adhesion (for example this "open blade" cheese knife). This is also part of the philosophy behind a Granton knife. A PTFE coating could be useful in this regard. Watermelons do have a tendency to stick to the sides of the blade, although I'd need to eat a lot of watermelon to want a dedicated watermelon knife.

I'd need to eat a lot of watermelon to want a dedicated watermelon knife.

It so happens we do have a dedicated watermelon knife! We also eat an abnormal amount of watermelon. As watermelon season will soon be upon us, I'll be sure to report on the efficacy of this product.

It actually looks as if this knife contains the various treatments Sam refers to in his post (in addition to its non-stick properties). It has holes in the blade, which minimize drag, and it has a Granton edge.

[Fat Guy]

Why would a nonstick coating be affected by sharpening? It's not the cutting edge that has a coating, and you don't sharpen the flat faces of a blade.

[gfweb]

That glass plate analogy doesn't sound right. Atmospheric pressure holds them together? Or is water just forming a layer that smooths surface irregularities in the glass and because of cohesion makes separation difficult? Of course I was never any good in physics.

[trekflyer]

Well, I've never heard this claim about pressure causing glass plates to stick together. From what I understand, it is the forces of adhesion between the water and the glass plates and cohesion between the water molecules that causes this. Generally these strong forces are caused by hydrogen bonds. Since two equally sized plates have a relatively large surface area for the cohesion and adhesion to occur upon, the force holding the two plates together is quite large. If we slide one of the glass plates along the plane between the plates, this will lower the surface area that is in contact between the two plates, it now requires less force to pull the two plates apart. Does this make sense?

[Fat Guy]

I'm hardly up on the science but I thought it was both: cohesion/surface tension AND atmospheric pressure, in other words if you go into space the two glass plates will separate but if you're under atmospheric pressure they still won't cohere without the layer of water.

[dcarch]

If you have two glass plates of 5" x 5" together with a drop of water in between, it will take about 350 lbs of force to overcome air pressure. However, according to the law of physics, it will take no force to work perpenicular against another force, therefore to get the glass plates apart, you just slide the glass plates away from each other. Water is a good lubricant. The glass plates act almost the same as suction cups in principle.

As a matter of fact, if you use two optical flat glass plates that are absolutely clean, you don't even need water in between.

dcarch

Air pressure experiement

[rotuts]

your excellent youtube demo does a good job of demonstrating air pressure.

however, two pieces of glass with water (or without water if 'perfectly flat') between then will still be very hard to separate in the vacuum of space.

they are easy to slide with water as a lubricant between them. Cant say how easy they will be to slide without that water, but Id guess it would be much more difficult.

[gfweb]

So there's 350lbs of atmospheric pressure? Doesn't sound right.

[dcarch]

So there's 350lbs of atmospheric pressure? Doesn't sound right.

I rounded it off. Atmospheric pressure (sea level) is 14.696 psi, less if you are on high altitude.

-----
however, two pieces of glass plates with water (or without water if 'perfectly flat') between then will still be very hard to separate in the vacuum of space.

----

That will be a function of water's tensile strength, which I don't know; how much force is required to stretch and break water. The fact is you need no power to separate the glass in vaccum. Water boils and expand very quickly in vacuum.

dcarch

Edited by dcarch, 28 March 2012 - 08:04 AM.

[rotuts]

wonder how the 'perfectly smooth' panes with no water would separate in a vacuum.

good point about the vapor pressure of water in a vacuum.