How often do you get roasted potatoes that look like they're going to be awesomely crisp only to find that rather than crispness, all you've got is a papery (or worse, leathery) skin on the exterior? Getting truly crisp potatoes is harder than it seems. Simply tossing them in a bit of oil and roasting them just doesn't work.
The problem is that with simple roasting, they'll crisp up all right, but the layer of crispness will be very very thin. Within moments, steam from the interior of the spud will cause the crisp bits to soften.
So what is it that makes a potato crisp?
Well, as I found out when exploring french fries last year, it's a dehydrated layer of gelatinized starch that does it. The thicker the layer of gelatinized starch you can build up, the crisper the potato. You accomplish this by parboiling the cubed potatoes, and just as with making french fries, adding a touch of acid to the boiling water acts as insurance against accidentally overboiling them—the pectin that holds potato cells together is strong in slightly acidic environments.
Want to know the secret to even crisper roast potatoes? Increase surface area. The more surface area a potato has for a given volume, the more bits there are to crisp up, and the crunchier it'll become. The potatoes above have been parbolied then tossed roughly in a bowl with a metal spoon until their surfaces have been roughed and scratched up. All those microscopic nooks and crannies will make for an extra crunchy surface.
You can use any type of potatoes you like for this, but there's a tradeoff:
- Starchy russet potatoes will produce the crispest crust because of their high starch content with fluffy, powdery interiors.
- Yukon Gold potatoes (what I've used here) will produce crusts that are still very crisp, but not quite as crisp as a russet. They'll also have interiors that are more creamy than fluffy. Some people like this contrast of textures. I'm on the fence, so usually alternate between the two varieties.
- Red waxy potatoes will have the creamiest texture of all, but will lack a very strong crisp crust. I don't recommend them for his purpose.
Next question: what's the best fat to use?
Well, if you can get your hands on it, this:
People often tout the awesomeness of duck fat and potatoes, and for good reason: it tastes awesome. Duck fat has a distinct richness and aroma that gets absorbed very easily into the surface of a spud. On top of that, it's got plenty of saturated fat and a high smoke point, which makes it an ideal medium for crisping up fried or roasted foods. (In general, the higher the saturated fat content of an oil, the more efficiently it'll crisp foods). Can't get duck fat? Well, turkey fat or chicken fat collected from roasted birds will do just fine.
Bacon fat or rendered lard are also fine choices, as are just about any sort of animal-derived fat.
If you must, extra-virgin olive oil will certainly do admirably well, though you won't get quite the same level of crispness you'd get out of an animal fat.
Once your potatoes are tossed in fat and seasoned well, all you've got to do is roast them in an extremely hot oven until they crisp up. (I do this while my turkey is resting.)
I roast mine directly on a heavy rimmed baking sheet (they have a tendency to stick to foil). The key is to make sure you let the underside crisp up completely before you even attempt to lift or flip them. If the potatoes don't come off relatively easily, you run the risk of breaking off the tops, leaving the crisp bottom cemented to the bottom of the pan. This is not an ideal situation.
Moral: your potatoes will release themselves from the pan when they're good and ready. Don't force them.
Finally, make way more than you think you'll need. Not only do these potatoes lose a great deal of volume as they roast, it also appears that your dinner guests suddenly gain a great deal of volume in their stomachs when the potatoes hit the table.
About the author: J. Kenji Lopez-Alt is the Managing Editor of Serious Eats where he likes to explore the science of home cooking in his weekly column The Food Lab. You can follow him at @thefoodlab on Twitter, or at The Food Lab on Facebook.