One of the reasons why I love to cook is one I have in common with people who knit: it is involving enough to keep your mind off world peace issues, but leaves enough mental space that you can wander, hold imaginary conversations, turn sentences around in your mind (everyone does that, right?), and generally putter about in the coziness of your own head.
Prepping vegetables launches me into such inner monologues, and in recent months they have been dominated by this nagging question: why does food stick to my knife, and how do I make it stop?
You know the phenomenon, I’m sure, but let me describe it for you: whenever I slice something (say, an onion or a zucchini), the pieces I’ve just cut tend to stick to the right side of the blade (I’m right-handed), so that when I’m cutting the next slice, the pieces that are stuck on there get pushed up and off by the new slice, and fall either to the right of my blade (unruly, but fine), or tumble off the cutting board and possibly onto the floor (messy), or fall to the left side of my blade, in which case I’m likely to cut into them again moments later (extra annoying).
After composing an imaginary email in my head over a few zucchini-slicing sessions (I eat a lot of zucchini), I finally sat down and wrote to Peter Hertzmann, the spectacularly knowledgeable creator of the à la carte website and associated blog, cooking instructor, and author of the must-own Knife Skills Illustrated, of which he kindly offered me a copy when we met in San Francisco a few years ago (more details about the book)*. And naturally Peter had answers, which I’m sharing below, mixed in with a few more tips I gathered in my research.
So, why does food stick to my knife?
The main reason is surface tension, a physical phenomenon that makes the surface of liquids resist an external force. In this case, it means that foods with a high water content (and many vegetables are more than 90% water) create slices with a moist surface that clings to the flat of the blade.
And how do I make it stop?
You could decide to subsist on low-water foods — I’m sure a diet of beef jerky and rice crackers will do you a world of good — or you could adopt one or more of these three strategies:
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