Tomato Sharpness

B

Barmaley

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Dec 31, 2016
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There is a consensus that the different knives need different sharpness of their edges. For instant a shaver blade has different needs than a chef knife. To determine knives sharpness they either measure the force needed to cut a thread or count how many times a knife can cut a rope. I wonder is there any technical terms of units of measure of kitchen knives sharpness so one could rank knives performance based on steel and way of sharpening?
 
My food prep is pretty basic, but every time I open a can with my knife it saves wear on my P-38.

Parker
 
catspa said:
My food prep is pretty basic, but every time I open a can with my knife it saves wear on my P-38.

Parker
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I like the off the wall answers. Almost hate to spoil the fun.

Tomatoes need a toothier edge. Push cuts need a polished edge. I used to grow tons of tomatoes before the deer got too bad and had a couple "tomato knives" that I kept at a level of just being able to draw across the tomato once to get a slice. If I took them to razor and polished sharpness they didn't work anymore. I had to leave them just a little toothy.
 
Hi I accidentally burned my mom's new kitchen knife that she got for Christmas. I don't have special cleaner. How can I fix this before she finds out.
 
krispykid said:
Hi I accidentally burned my mom's new kitchen knife that she got for Christmas. I don't have special cleaner. How can I fix this before she finds out.
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hey buddy, try using some rubbing alcohol or a small amount of vinegar and be careful!
 
The measures would be sharpening grit, angle, and edge width. Grit and angle are pretty easy as one chooses them when they sharpen. Edge width requires a very good and expensive microscope and someone who can use it. Edge width can be approximated by using the pressure to cut thread on a scale.

The more specialized the knife, the better one can make it perform its duties but the less it is able to perform outside those duties.

For instance if I had a knife dedicated solely for use in cutting tomatoes and similar soft fruit in a kitchen setting, I’d use a fine stone, get it as sharp as possible, and use an edge angle of about 5 degrees per side. Also, it would be stainless steel. Corrosion will dull that knife faster than anything else. However, I wouldn’t be able to use it for much else.
 
This is what I've done with my kitchen knives, all of which are inexpensive stuff in simple stainless steels:
Set the edge on a Fine India stone (360-400) at 30° inclusive or lower. Do as much deburring on the stone as possible. Some stropping on clean paper laid over the stone works well for whatever burrs or remnants may be left. Test how it cuts in fine paper, like phonebook pages, catalog pages, thermal receipt paper, etc. Should slice cleanly, effortlessly & repeatably through the paper to pass the burr test as well as verifying the edge is fully apexed and clean.
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^That alone is enough for 'tomato sharp'. For periodic upkeep after setting the edge, a few passes on a medium or fine ceramic rod or steeling on a quality kitchen steel will easily keep it in tomato-slicing shape and even enhance it a bit.

Slicing tomatoes is all about keeping the apex very keen and aligned straight, and less about the finish (grit-wise). If using blade geometry that's sort of thick or wide-angled at the edge, some toothy bite helps to get it started in the cut. But slicing tomatoes will get progressively easier the thinner the blade & more acute the edge geometry become; and the edge finish - whether it's toothy or polished - will become less of a dominating factor. So long as the apex is keen and stable and aligned straight, the thinner geometry will make most of the additional difference in enhancement, after that.
 
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As far as testing edge retention of kitchen knives, I'd say slicing a bunch of carrots would be a good test. Use the same section of the blade to cut a carrot into 30 or so slices and then BESS test and compare.
 
Barmaley said:
I wonder is there any technical terms of units of measure of kitchen knives sharpness so one could rank knives performance based on steel and way of sharpening?
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I don’t think of kitchen knife sharpness this objectively, but that’s just me. Most of my knives were purchased used, or self-made, and few of them do I know what steel they are.

Does my tomato knife cut tomatoes satisfactorily? Yes=good, let’s get on with it. No=How can I fix it? Then let’s get on with it.

Don’t get me wrong, I can geek out about edges as well as the next guy, I just don’t do it in the kitchen. Food is fuel to me, not a dining (or prep) experience.

That said, I did build a two sided magnetic knife rack, that holds about 3dozen knives - stainless on one side, carbon steel on the other. Most commonly I’ll use a carbon steel knife to cut meat, and a stainless knife on fruits or vegetables. Don’t know why, just a habit. Perhaps I subconsciously think that any meat residue will add a little rust protection.

Too old to rumble now, at my age it’s all grumbling. Unlike Killgar, I have no cool switchblade for my tomatoes. Instead I use a heavily modified 8” Farberware serrated bread knife. Serrations gone, edge thinned down to about 18°, very slight convex at 400 grit. Lightly burnished on a smooth steel, I find it quite satisfactory for slicing tomatoes and other vegetables. Not bad for a knife I almost threw in the scrap bin, it was a real dog when I got it. Now it’s useful and proud.

Parker
 
Squishier things - raw meat, veggies that are over ripe - favor a toothier edge, regardless of steel.
As mentioned, style of cutting matters too. Push cuts and chops favor a more polished edge. So a chuka-bocho can be more polished than a slicer.
 
Obsessed with Edges said:
This is what I've done with my kitchen knives, all of which are inexpensive stuff in simple stainless steels:

^That alone is enough for 'tomato sharp'. For periodic upkeep after setting the edge, a few passes on a medium or fine ceramic rod or steeling on a quality kitchen steel will easily keep it in tomato-slicing shape and even enhance it a bit.

Slicing tomatoes is all about keeping the apex very keen and aligned straight, and less about the finish (grit-wise). If using blade geometry that's sort of thick or wide-angled at the edge, some toothy bite helps to get it started in the cut. But slicing tomatoes will get progressively easier the thinner the blade & more acute the edge geometry become; and the edge finish - whether it's toothy or polished - will become less of a dominating factor. So long as the apex is keen and stable and aligned straight, the thinner geometry will make most of the additional difference in enhancement, after that.
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I definitely steel my tomato knife after each use. 3-4 passes on each side before I put it away.
 
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