10.3 Low temperature and sous vide

How sous vide works

Sous vide cooking runs in four steps:

• The food goes into a food-grade plastic bag.
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• The air is sucked out and the bag is sealed.
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• The bag goes into a water bath.
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• The water is held at a precise temperature, the one you want the food to reach.
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The right setting depends on the result you are after.

The water heats the food through the bag but never touches it. So nothing in the food can dissolve into the water and be carried off. The food keeps more of its flavor.

Fruits and vegetables

Blanching and steaming soften vegetables, but they wash out vitamins and minerals. Sous vide softens them and keeps more of those nutrients. One reason is that the bath stays below the heat at which the cell walls break down completely. So the food becomes tender but keeps some of its shape. Another reason is the bag: any nutrients that do leak out stay inside it.

Fruit cooked at a low temperature can also take in flavor. Put a liquid in the bag with it.

Two things in plants keep them crisp: pectin and starch. Pectin is the gelling agent that gives jam its set. Pectin breaks down at 83°C (183°F), and it does so more slowly than the starch. The result is often a tender fruit or vegetable with an unusual texture.

With fruits and vegetables, time and temperature are not a safety question. What they change is the structure.

Custards

A custard is easiest to think of as a texture: smooth, rich, with a particular feel in the mouth. Cooks have made custards for centuries by gently cooking eggs with milk and heavy cream. Today there are many other ways.

Sous vide can make many custard-type preparations: sabayon, curds, crème anglaise, dulce de leche, and bases for custards and for ice cream. It gives a more even result every time, and better control of texture. That texture can be light and airy, as in a sabayon, or thick and dense, as in a posset.

The eggs in a custard are properly cooked at 82°C (180°F). Set the bath to that, and the custard cannot overcook.

Every custard has plenty of fat. Fat gives the rich mouthfeel. It also carries flavors and aromas that dissolve in fat.

A lighter custard can be cooked sous vide, chilled, and then put through a whipping siphon. It comes out as a smooth, creamy foam.

Other uses of the vacuum sealer

Compressing fruit. A vacuum chamber lowers the air pressure around the food. The air and water inside the plant tissue swell fast and burst the tiny spaces that hold them. When normal pressure comes back, those spaces collapse. Light now passes through the food instead of scattering, so it looks see-through. The texture changes too: it becomes denser, with more bite. Watermelon is a well-known example.

Infusing. Seal a food in a bag with a liquid, and the vacuum pushes flavor in quickly. This works best on porous foods, for example spices in cream or herbs with melon. It is faster than a traditional infusion.

Practice