20 November 2014

Knives: Cuts and sharpness

Some time ago I got interested in improving my kitchen cutting technique,  mainly cutting-board cutting.  So I looked what youtube had to offer.  Cutting an onion on youtube is nearly a standard but there is not much variation on it. Or rather any demonstration not perfectly meeting the standard will massively be downvoted by professionals and youtube specialists alike unless it concerns a Japanese suchi champion.

The cuts.  Knife cuts get really interesting when spooncarving and such high risk activities with its numerous variations.  When cutting to the board I see three main movements:  1. The push-cut straight down to the board, that's also chopping.  2.  Slicing,  moving the knife moves mainly forward from tip to heel or vice-versa. There is also repetitive-slicing (sawing) as a variation on slicing, I use it when cutting large peaces of meat or bread or with a blunt knife. 3. The skewed cut,  when the tip rests on the board and the knife is pulled backward.
Important is that a knife may be too blunt for a push cut and be perfectly fine with slicing and skewed cuts.

Cutting and sharpness.  A sharp knife is a safe knife and all that.  But things are not that simple.  This picture from a video by Virtuovice shows a razor sharp knife doing a push-cut through an apple.  I don't think the sharpness of the blade is of any help, a completely blunt but narrow knife would cut better and straighter. For Virtuovice it's probably not a problem as he uses his knives to cut meat.  When peeling the apple,  still a push-cut, the sharp edge can be used as the thin peel can be pushed away. But here again a thin, narrow bladed parring knife will be in line with the cut and need less effort.
When parring I look for a balance in sharpness.  If the blade is too sharp I will cut my fingers who are holding the apple,  too blunt and I will need to saw cut to peel.  So I need a Goldilocks blade able to push cut the apple,  but not my fingers.  When cutting to the board,  my fingers are less at risk. I then can go for a sharper blade or I can use the more effective slicing and skewed cuts.

Cutting an onion  After trying out the big (chef's) knife approach,  I came back to using a paring knife to cut vegetables on the cutting board. And that's what most people I know do.  I go for a medium sharpness,  sharper than many households here but less than many professionals and certainly less than some sushi knives.

A sharpish thin bladed parring knife can cut onions like butter and gives a good result,  a chef's knife is not  necessarily better or easier. The cut used is a folded cut: from the tip slicing until nearly touching the board coming back with a skewed cut. And maybe there are less tears when the open onion surface is minimal.

As a matter of fact the same cutting technique with a ten year old factory edge (that's blunt) table knife is no fun,  but still offers acceptable results.
An ever harp knife
I sometimes hear people claim to never sharpen their parring knife.  Mostly it concerns the (razor) thin carbon version of the parring knife I use with an edge of maybe 5 degrees per side.
Looking at Cliff Stamp post about edge retention at lower angles, one can see a confirmation of that as their is a clear distinction between 25 dps and 13 dps.  13 dps cuts on and on,  only slowly achieving a too blunt state, where the edge of 25 dps dissapears fast to an unusable state