A new kind of potato for frying, packaged raw, absorbs less oil than frozen fries.
MANY OF THE FRIES SERVED TODAY in restaurants in France come out of a vacuum-sealed bag. Home cooks still prefer to use fresh potatoes because they soak up less oil. Will traditional practice give way to the new technique of packaging sliced potatoes raw under a controlled atmosphere, developed in 1997 by Patrick Varoquaux and his colleagues at the Institut National de la Recherche Agronomique (INRA) station in Montfavet?
In cafeterias and restaurants at least there is no avoiding the superior convenience of precut and processed potatoes because the large volumes consumed take extensive advance preparation. Another complication is that potatoes darken upon exposure to the air once they have been cut up because slicing releases enzymes and associated substrates that otherwise are shut up in separate compartments in the cells of the potato. In the presence of oxygen these molecules react and form brown compounds similar to the ones that cause our skin to tan in the summer.
Before Varoquaux’s work, this enzymatic browning prompted the makers of prepared fries to offer precooked products: The potato sticks were peeled and sliced, then dried and deep-fried in oil (often palm oil, cheaper than other kinds), and finally frozen. For the final cooking they could either be deep-fried again, in which case the microscopic fissures created during freezing caused them to absorb a lot of oil; or reheated in the oven, in which case they ended up being too dry.
Atmosphere of Fries
In their search for ways to remedy these defects, the INRA chemists experimented with the idea of packaging raw sliced potatoes under controlled atmospheres—what are now known in Europe as quatrième gamme fries—taking care to monitor signs of browning during fabrication.
To minimize browning, a number of steps are followed. First, the potatoes must be carefully peeled, preferably under a stream of water, so that the cellular structure is not damaged. For this reason the blades of the stainless steel knives used to cut the potatoes into sticks must be kept as sharp as possible.
Next the individual sticks are kept at a temperature of about 4°C (39°F) so that the metabolism of the intact cells is slowed down as much as possible. After draining by either centrifugation or ventilation, the potatoes are treated with an inert gas, in the absence of oxygen, in a perfectly sealed packet. In this way the sticks can be preserved for 10 days, still at 4°C (39°F), without alteration (in the course of storage, however, the tissues of the potato accumulate sugars that cause the fries to darken during cooking, by reactions analogous to those that brown the crust of bread). The flavor and texture of fries that are cooked later nonetheless resemble the flavor and texture of fresh French fries: The proportion of oil absorbed is similar, much less than in the case of frozen potatoes that are deep-fried.
Deep-Frying Considered
How should French fries be cooked? On this point cooks are apt to disagree, for each chef has his or her own method. One needs to ask what one is looking for in a plate of French fries and then rationally to examine which procedures allow this expectation to be satisfied.
Few connoisseurs will quarrel with the opinion that good French fries must be tender at the center, with minimal greasiness, and that they should be crispy without being overly brown. To achieve this result we must recognize that deep-frying involves a diffusion of heat from the outside inward, with two principal consequences: the formation of the crust and the cooking of the interior.
Potatoes are composed of cells that contain mostly water and starch granules. When the heat reaches the center of the fries by conduction, some cells are dissociated as the starch granules release their long molecules into the heated cellular water. With the complete evaporation of this water a crust is produced on the surface of the fries.
If one cooks a potato stick into which a thermocouple has been inserted (a more rapid and more reliable way of measuring temperature than with a thermometer), one finds that the interior heats up very slowly: Even when the temperature of the oil is 180°C (356°F), the temperature in the center reaches 85°C (185°F) only after several minutes, for the potato is thermically inert. In other words, if the oil is too hot in the first round of frying, the surface will burn before the inside is cooked.
Conversely, the oil must not be too cold to begin with, for then the crust will be slow to form and the fries will soak up oil. In practice, seven minutes of cooking at a temperature of 180°C (356°F) yields good results for fries measuring 12 millimeters (about half an inch) thick. A second round of cooking in oil heated to a slightly higher temperature, 200°c (392°F), produces perfect fries; remove them from the oil when they have turned just the right golden brown color.