Maillard Reactions

• Two browning processes take place when you fry your potatoes. The first is called Maillard reactions, a set of molecular changes that take place in starches and proteins as they cook. Some of those molecules break down under the fryer's intense heat, splitting into fragments that re-join in new and more complex combinations. Some of those deconstructed molecules turn brown, while others help create the toasty, savory flavors that mark a good potato chip or french fry.

Caramelization

• The other cause of browning is caramelization, a similar process that takes place in the potato's sugars. Like the proteins in a Maillard reaction, the sugars in your potato break down into smaller components that recombine in different ways to provide browning and new flavors. In some potatoes, especially russets, the sugars can sometimes become a problem. If the potatoes have been stored in a cold environment, such as a refrigerator, they'll be too sugary to fry well. They'll turn a disconcertingly dark brown well before they're properly cooked. A few weeks' storage at room temperature fixes the problem, but it can be maddening.

Browning French Fries

• Many restaurants make excellent french fries despite these difficulties, following a well-recognized technique. First, the potatoes are precooked or "blanched" in relatively cool oil, at about 300 degrees Fahrenheit. This cooks the potato all the way through, and provides an opportunity for moisture in the outer areas of the fry to evaporate. That's important, because until the surface of the potato dries out, neither caramelization or Maillard reactions can occur. When the blanched potato is later fried in hotter oil at 350 F, the remaining moisture quickly evaporates and permits the familiar golden-brown crust to form.

Potato Chips

• Whether you think of "chips" as something that comes with fish or something that comes in a bag, the basic principle is the same. Potato chips are made with potatoes sliced extremely thin, so thin that blanching them isn't necessary. Instead, the slices are dropped directly into hot oil. Each chip has minimal depth and lots of surface area, so its moisture evaporates almost immediately. The now-dry surface of the chip quickly rises to the temperature of the surrounding fat, triggering caramelization and Mailard reactions. If the chips are lifted from the oil and drained carefully at the right moment, they'll retain their crisp and delicate texture as they cool.