types (true new potatoes and common U.S. red- and white-skinned varieties), neighboring cells cohere even when cooked, which gives them a solid, dense, moist texture, and holds them together in intact pieces for gratins, potato cakes, and salads. Both types can be made firmer and more coherent, less prone to the “sloughing” of outer layers when boiled, by treating them to the low-temperature precooking that strengthens cell walls (p. 283).
Cooked potatoes sometimes develop a large internal region of bluish-gray discoloration. This “after-cooking darkening” is caused by the combination of iron ions, a phenolic substance (chlorogenic acid), and oxygen, which react to form a pigmented complex. This problem can be minimized in boiled potatoes by making the pH of the water distinctly acidic with cream of tartar or lemon juice after the potatoes are half-cooked.
The flavor of boiled potatoes is dominated by the intensified earthy and fatty, fruity, and flowery notes of the raw tuber. Baked potatoes develop another layer of flavor from the browning reactions (p. 777), including malty and “sweet” aromas (methylbutanal, methional). Leftover potatoes often suffer from a stale, cardboard-like flavor that develops over several days in the refrigerator, but within a few hours if the potatoes are kept hot for prolonged service. It turns out that the aromatic fragments of membrane lipids are temporarily stabilized by the tuber’s antioxidant vitamin C; but with time the vitamin C is used up and the fragments become oxidized to a series of less pleasant aldehydes.
Potatoes are prepared in many ways, and used as an ingredient in many dishes. Here are brief notes on a few starring roles.
Mashed and Pureed Potatoes There are many different styles of mashed potatoes, but all of them involve cooking the potatoes whole or in pieces, crushing them to a more or less fine particle size, and lubricating and enriching the particles with a combination of water and fat, usually in the form of butter and milk or cream. Some luxurious versions may be almost as much butter as potato, or include eggs or egg yolks. Mealy types fall apart into individual cells and small aggregates, so they offer a large surface area for coating by the added ingredients, and readily produce a fine, creamy consistency. Waxy potatoes require more mashing to obtain a smooth texture, exude more gelated starch, and don’t absorb enrichment as easily. The classic French pommes purées, pureed potatoes, are made from waxy potatoes, pieces of which are pushed through a fine sieve or food mill and then worked hard—to the point of having what an eminent French cookbook writer, Mme Ste-Ange, called a “dead arm”—first alone and then with butter, to incorporate air and obtain the lightness of whipped cream. American recipes take a more gentle approach, sieving mealy varieties and carefully stirring in liquid and fat to avoid excessive cell damage, starch release, and glueyness.
Fried Potatoes Fried potatoes are some of the world’s favorite foods. Deep-fried potato sticks and slices and the technique of double-frying were all well known in Europe by the middle of the 19th century, and in England were attributed mainly to the French: hence the term “French fry” for what the French simply call fried potatoes (pommes frites). These products happily turned out to be among the few foods whose quality need not be compromised by mass production. Of course they’re rich: the frying oil in which they’re immersed coats their surface and is drawn into the tiny pores created when the surface dries out. The proportion of oil to potato depends on the surface area. Chips, which are almost all surface, average about 35% oil, while thick fries are more like 10–15%.
French Fries “French fries” may first have been made in significant quantities by Parisian street vendors early in the 19th century. They are potato sticks cut with a square cross section, 5–10 mm on a side,