Step One: The Raw Ingredients

Success begins with a careful selection of materials. Karen Schaich, a professor of Food Chemistry at Rutgers University (currently in the process of publishing a USDA-funded paper on the chemistry of French-fry crust), says that selecting a good potato is one of the most important steps in making a good fry. "You have to have a high-density potato, like a Russet Burbank," she says. "It's kind of like apples: Some are hard and dense and crisp. Soft, mealy apples brown a lot faster, and the same thing is true with potatoes. If you've got a soft potato, make mashed potatoes."

High-density foods are best for frying because if the item is too soft when tossed in the vat, the oil will soak through, making it difficult to attain a crispy crust at the surface and resulting in a soggy, oil-logged product.

Step Two: The Oil

In the world of fried food, oil makes or breaks a dish. Michael Blumenthal, an award-winning food-science researcher, devoted much of his life to analyzing the chemical properties of optimal frying oil and even developed a bell curve outlining the different stages of oil degradation.

Turns out that although selecting the right oil is important (predictably, saturated fats do best because of their chemical stability), the focus should be on how much the oil has been used. Fresh oil, for instance, is known to be useless. Polar water and nonpolar oil will repel, and since most foods (potatoes included) contain significant amounts of water, there is no basis for good contact between oil and raw product. In the case of the French fry, fresh oil gives an undercooked product that's "still a little bit of a log," Blumenthal says. "If you try to flex the fries, they actually snap."

Only once the oil begins to break down under heat will the two ingredients attract enough to allow good contact. Then hydrogen bonding enables the heat from the oil to transfer to the surface of the food, where it will volatilize the water and dehydrate the surface (leading to the initial phases of what we consider "crispiness").

But let the oil degrade too much, and things go rapidly downhill. Food becomes dry and, in the case of French fries, will even hollow out in the middle, forming a kind of tube. "Those degradation products, when eaten, produce what I call jelly belly—most people just refer to it as the runs," Blumenthal says. Schaich says oil at this stage tastes a little acrid, grassy and rancid—almost burned.

Because frying requires so much oil, people are tempted to save the oil for later use. They put it in a container, toss it in the fridge for next month's cookout and walk away. But Schaich warns that placing oil in the fridge is not like pushing a pause button on degradation. "Once you start it, you can't stop it. Even if it's slow, it will continue to degrade in the refrigerator." Unused oil can also degrade if it's in a plastic or an otherwise permeable container (as opposed to glass), because oxygen can diffuse through. "Better to buy oil in smaller quantities and use it faster," Schaich says.

Step Three: The Heat

Now it's time for the actual cooking. Some places, like McDonald's, get a head start, blanching the fries in 170-degree water, frying in 365-degree vegetable oil for 50 seconds and then freezing. This pre-fry ensures that the fries will be cooked through to the middle on location, and freezing converts the potato's moisture into ice, harming the cellular structure of the potato and making it easier for the water to be released when it's converted to steam through heating.

For the main cook, McDonald's fries at 360 degrees for about three and a half minutes. Some experts recommend adding vinegar to the oil to slow the breakdown of pectin (the polysaccharide that helps a potato keep its structure intact). Try as you might, though, industrial fryers will nearly always beat out whatever equipment you've got at home. Commercial fryers come with built-in temperature controls that automatically shut off if the oil reaches dangerous temperatures. The quantities of fries that go in and out of a restaurant's giant fryer far exceed whatever you'll be producing at home, enabling them to recycle old oil without storing it for weeks inside a refrigerator.

Step Four: Cleanup and Safety

If you're a brave soul planning to bring home the show, steer clear of some common fried-food mishaps.

Stay Away From the Oven

Oil draws in a substantial amount of energy in a microwave or an oven—much more than water. When an oil-heavy product is placed in the oven, without much water to evaporate, the oil heats up quickly and can burst into flame. "Many household fires have been started by people putting things in the oven that contain a substantial amount of oil," Blumenthal says.

Be Patient

Because fried foods cater to mass-production enterprises that can use lots of oil rapidly at its optimum stage, home frying should not be expected to yield the same quality product. You can start off in the right direction by allowing oil to heat up and form polar products before dumping in the fried-food-to-be, but expecting to use oil at its prime stage is a bit impractical. It can take days for oil to degrade enough to generate a truly optimal result, and restaurants have the advantage of being able to recycle and use their oil fast enough to beat the degradation process. Consider it a tradeoff for your home's improved ambiance.

Proper Clean Up

Many people are tempted to clean their deep fryer by dunking it in water. This is not advisable. "Residual materials will remain in the circuit, and when it's plugged in next time it can start a fire or cause strange odors to appear," Blumenthal says. It's best to leave water out of the equation and simply wipe down the fryer, allowing for a clean start the next time around.

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