Cooking for Geeks: Real Science, Great Hacks, and Good Food (65 page)

Using food as a serving bowl is nothing new: stew in a bread bowl, sliced fruit in half a cantaloupe, and now, brownies in an orange.

Cut the top off and trim out the center.

Fill with brownie mix (guilty pleasure).

Bake until a toothpick inserted 1” / 2.5 cm deep comes out clean. Dust with powdered sugar.

With a name like “sous vide,” this cooking technique sounds foreign, and for good reason: the French chef George Pralus introduced it to the culinary world in the 1970s. While foreign in origin, it is certainly not complicated or mysterious. At its simplest, sous vide cooking is about immersing a food item into a precisely temperature-controlled water bath, where the temperature is the same as the target temperature of the food being cooked. Translation? Ultra-low-temperature poaching. And since the temperature of the water bath isn’t hotter than the final target temperature, the food can’t overcook. Sous vide cooking essentially locks the variable of temperature in the “time * temperature” formula.

The temperature of the water bath is chosen to trigger chemical reactions (e.g., denaturing, hydrolysis) in some compounds in the food while leaving other compounds in their native state. It is one of the biggest culinary revolutions to hit the commercial cooking scene in the past few decades, but has appeared in the U.S. only recently. If I could pick only one new cooking method out of this entire book for you to try, sous vide would be it, hands down. The reason sous vide is so, well, amazing is that foods cooked this way have no gradient of doneness and the associated overcooked outer portion. Instead, the entire piece of food has a uniform temperature and uniform doneness.

The name sous vide (meaning “under vacuum”) refers to the step in the cooking process where foods are placed in a vacuum-pack plastic bag and sealed. Using a vacuum bag — a plastic bag that is sealed after all the air in it has been removed — allows the water in the bath to transfer heat into the food while preventing the water from coming into direct contact with it. This means the water does not chemically interact with the food: the flavors of the food remain stronger, because the water is unable to dissolve and carry away any compounds in the food. (Sous vide is a funny name; I think it should have been called “water bath cooking,” because the actual heat source is usually a bath of water. Bain-marie was already taken, I suppose. Still, as with the name “molecular gastronomy,” once something gets popularized, it tends to stick.)

Foods cooked sous vide have no temperature gradient, meaning that the entire portion of food is cooked to a consistent level of doneness.

Sous vide cooking doesn’t have to be done with a sealed bag in water. A few items don’t need to be packed at all. Eggs, for example, are already sealed (ignoring the microscopic pores), and when using this technique for secondary applications like preheating vegetables such as bok choy for steaming, there’s no benefit to sealing the food in plastic.

The steak tip on the left was cooked sous vide at 140°F / 60°C; the one on the right was pan-seared. Note that the sous vide steak has no “bull’s eye” shape — that is, it’s consistently medium-rare, center to edge, while the seared steak is well-done on the outside and rare in the middle.

You can also use other fluids instead of water: oil, for example, or even melted butter. And because meats don’t absorb fat the same way that they can water, when using one of these as the liquid medium some applications can skip sealing. This can be extremely useful for those foods that might be difficult to seal. Chef Thomas Keller, for example, has a recipe for poaching lobster tails in a bath of butter and water (
beurre monte
, melted butter with water whisked in, which has a higher burning temperature than butter alone).

Temperature-controlled air would technically work as well, but the rate of heat transfer is much, much slower than for water — roughly 23 times slower. Given the low temperatures involved, something like chicken in a 140°F / 60°C “air bath” would take so long to come up to temperature that bacterial growth would be a serious concern. Using a liquid such as water ensures that heat can penetrate the food via conduction — liquid touching plastic touching food — rather quickly. Water is cheap and easy to use, so you’ll almost always see it called for, but some chefs do occasionally use other liquids.

The classic example given to explain how sous vide cooking works is cooking an egg. Since different egg proteins denature and coagulate at slightly different temperatures (most are in the range of 144–158°F / 62–70°C), holding an egg at various temperatures within that range will result in varying consistency of egg white and yolk. (Refer back to the discussion of egg proteins setting at different temperatures in
144°F / 62°C: Eggs Begin to Set
in
Chapter 4
.)

To some, a “perfect” soft-cooked egg should have a slightly runny, custard-like yolk and a mostly set white. Cooking an egg in water brought to a boil can result in an overcooked end result, because the temperature of the egg ramps up to boiling point until it is pulled out. In sous vide, the temperature of the egg reaches only the ideal temperature of the cooked egg, so it cannot overcook.

Cooking eggs in a sous vide bath at 144.5°F / 62.5°C.

By immersing the egg in a water bath held at that temperature you ensure that the egg cannot get any hotter, so in theory, those proteins that set at a higher temperature will remain in their native form. In reality, most chemical reactions in cooking aren’t specific to a particular temperature, but are dependent on time-at-temperature. In practice, though, this simple model is accurate enough to explain how sous vide cooking works.

For a “perfect” soft-cooked egg, try cooking it sous vide at 146°F / 63°C for one hour. Because eggs contain many proteins that set at slightly different temperatures, you can experiment by adjusting the temperature up or down a few degrees to suit your personal preferences.

For other foods, consider the compounds they contain, determine the temperatures at which the compounds undergo their different transformations, and pick a temperature high enough to trigger the reactions you do want, yet low enough not to trigger the ones you don’t.

Sous vide cooking isn’t a magic bullet, though. For one thing, the textures of some foods break down when held at temperature for any extended period of time. Some types of fish will break down due to enzymatic reactions that normally occur at such a slow rate that they are not noticeable in traditional cooking methods. Sous vide also doesn’t reach the temperatures at which Maillard reactions or caramelization occur; meats cooked sous vide are commonly pan seared or even blowtorched briefly after cooking to introduce the flavors brought about by these browning reactions. The largest drawback, however, is the requirement to pay serious attention to food safety issues and pasteurization.