Frying potatoes: how complicated can it be? You take a potato, slice it into strips, fry until crisp and golden, drain, and serve. Nothing to it, right?
Actually, there is quite a lot to it. Yes, making great fries is easy once you have a good recipe in hand, but there’s a lot of unseen action driving this seemingly straightforward process, and knowing what’s happening can help you get potatoes that are crisp and light, not limp and soggy. It starts with choosing the right potato.
Choose high-starch potatoes for frying
Probably the biggest factor to consider when picking a potato is its starch content, which is a good indicator of how it will cook. High-starch potatoes have, as you would guess, more starch than some varieties and a little less water. This combination makes them perfect for very crisp fries (as well as for dry, fluffy baked potatoes). Low-starch potatoes, on the other hand, have less starch and more moisture. They’re great for boiling, but they make limp, soggy fries.
High-starch Russet Burbanks are especially good for frying. Not only are they packed with starch granules, but the granules are larger than in other varieties. Russet Burbanks (also called Idahoes or simply russets) absorb less fat, cook in less time, and make lighter, crisper fries that are less prone to being limp or greasy.
When potato strips are dropped into hot oil, the sudden high heat turns moisture near the potatoes’ surface into steam, which pushes outward, causing bubbles and that familiar sizzle. Water in the center of the potato rushes out to the surface to replace what has been lost. This steam does two things. It gets rid of most of the free internal moisture and allows only a small amount of oil to be absorbed on and near the surface. As long as there’s pressure from steam pushing outward, the oil can’t enter the potatoes.
As frying continues (or during the high-temperature second frying—a technique I’ll discuss in a moment), something different happens with the water. Starch granules on the surface absorb the surface moisture and expand. With this swelling, the surface seals so oil cannot enter, and any remaining moisture gets trapped inside. Russet Burbank potatoes, with their large starch granules, can absorb all of that trapped internal water to produce a crisp fry with a dry interior.
In contrast, fries made with lower-starch/higher-moisture potatoes get brown before they lose all their moisture. They tend to turn limp after standing a short time because of the steam trapped under the surface. These principles apply not just to deep-frying, but to pan-frying as well.
Cold storage turns high-starch potatoes into low
The ideal storage condition for potatoes is a cool (45° to 55°F), dark place. If potatoes are held below 40°F, some of the starch breaks down into sugars. If you fry these potatoes, the increase in sugar causes them to brown too fast, before they cook through in the center. Fortunately, storing the potatoes in a warmer place for a few days will revert the sugars to starch.
Long and skinny fries cook faster
Fried potatoes come in many shapes and sizes, but the classic long, thin french fry is an ideal shape because it has so much surface area. This means faster cooking time, rapid moisture loss for crisp fries, more exterior for those sweet, crisp, great-tasting browning compounds to form, and, admittedly, a larger area that can absorb oil.
If you rinse or soak in water, be sure to dry well
There is some controversy over whether rinsing potatoes makes a difference. Rinsing removes the starch on the potato’s surface; these surface starches can cover the natural sugars and proteins that cause browning, so it’s possible that rinsing enhances browning.
Drying the potatoes after rinsing is crucial. Water on the potatoes’ surface causes the temperature of the cooking oil to drop. This means a longer cooking time and more fat absorption. Water also reacts with the cooking oil, forming contaminants that lower the oil’s smoke point.
Perhaps most important, water on the surface can inhibit crispness and produce greasy fries. Remember that the surface starch absorbs nearby moisture and seals the surface. If you don’t dry the potatoes, you won’t get a dry surface that seals.
For crisp, firm fries, fry twice
Double frying can ensure outstanding fries. The first fry at a lower temperature cooks the potatoes through and greatly reduces their internal moisture, drying them out. The second fry at a higher temperature browns and crisps the fries. Ideally, this is when the surface starch absorbs the last remaining bit of moisture, expands more, and seals the surface for crispness.
You do need to have the cooking time for high-starch potatoes just right. If you cook them too long, they’ll run out of internal moisture. Without this moisture to turn to steam pushing outward, the fries become greasy.