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Cooking in a vacuum

Over the years, countless changes have occurred in the industry, and the need to prepare safe, consistently seasoned food using a minimum of human and fossil energy has led to modern, innovative methods of food preparation. Many eating establishments, from the corner diner to the busiest Michelin three-star restaurant, are embracing a cooking technique known as sous vide.

French for “under vacuum,” sous vide entails cooking foods that have been placed in special bags and then into a vacuum-sealing machine that, through the use of pressure, removes all of the air. The bag is then transferred to a moist, temperature-controlled environment to cook. Combi ovens are often used, since they can be set at steaming temperatures below 180°F and have built-in thermometers capable of tracking internal temperatures. Circulators are also frequently employed. Originally found in laboratories, these units consist of a heating element and pump to accurately circulate and heat quantities of water to precise temperatures. Relatively small, they can be easily attached to plastic containers and used wherever there is a power source.

Placing Food Under Pressure

When food is vacuum-sealed in a bag, several things happen. Air is removed, creating a vacuum; the food is compressed in the bag; and pressure—determined by recommended settings—is applied to the product.

Whereas a bag of coffee beans that is vacuum-sealed at high pressure is hard and dense, a slice of watermelon similarly treated will be crushed, flattened and compressed to create a new and interesting texture. Understanding this force or pressure is important when exploring which items to vacuum seal. Care must be taken with delicate products. For example, fish fillets can be sealed on specially designed, reusable hard plastic trays, or even cedar planks to maintain their shape. Cures and marinades work exceptionally well under vacuum. Gravlax, normally cured in a sugar, salt and dill mixture for up to three days, can be finished in one day. Using this technique for marinating meats is excellent; fewer ingredients and less time are needed and food does not oxidize.

The Benefits of Vacuum Sealing

Since storage space in any kitchen is a prime consideration, vacuum-sealed foods have a distinct advantage: they take up far less room, can often be stacked, are easily cooled down in ice baths and are clearly identifiable in any walk-in or refrigerator. A prime example of the machine’s ability to cut down on needed storage space is the familiar television commercial that shows compressed and bagged blankets and sweaters getting stowed neatly under the bed. For sous vide cooking, a variety of bags are used for vacuum sealing, each designed for specific pressures and heat ratings—normal storage bags cannot be used in these machines. Perhaps the most important function of the vacuum sealer is to eliminate the oxygen that bacteria require to live and reproduce, thus increasing the shelf life of food. Hotel pans full of crème anglaise or pastry cream can be virtually pasteurized in the vacuum sealer—the liquids bubble as air is forced out. Interestingly, not all bacteria require oxygen to survive. Anaerobic bacteria such as clostridium botulinum can multiply in an oxygen-free environment, producing a deadly toxin. Hence, it is extremely important to package all foods under strict sanitation.

Vacuum sealing is not appropriate for food preservation.

Many machines have an attachment that allows inert gas such as nitrogen to be injected into the packaging. Referred to as modified atmosphere packaging, this is a common technique used in commercial foods to lower the pH and inhibit bacterial growth. In addition, modern vacuum sealers have computer ports, making HACCP documentation easy and efficient.

Cooking at Exact Temperatures

Because we now have the ability to control foods’ environment and achieve exact cooking temperatures, a new realm of flavor and texture is possible. The high-heat temperatures typically associated with searing, braising and barbecuing (180°F to 210°F) tenderize the connective tissues of meat but also force out moisture, making it dry. The sous vide method allows us to cook to the exact desired temperatures while increasing the time—without fear of overcooking. Once a chef determines the specific desired temperature for the meat, it cannot overcook—it will always have a consistent appearance of doneness throughout the slice and is not subject to carry-over cooking. The searing of a grilled steak can be done right before service by simply removing the product from the circulator and finishing it in a pan or on the grill. Searing can also be done before the item is put in the bag. However, it is extremely important to chill all foods to 40°F before vacuum sealing. If foods are sealed hot, water vaporizes at the reduced temperature, drying out and changing the textures of the foods.

The Danger Zone: 41° to 135°F

Regardless of what or how food is cooked, the temperature danger zone must be adhered to at all times. FDA code requires that all foods be cooled from 135°F to 70°F within two hours and from 70°F to 41°F within an additional four hours. If the food is not cooled from 135°F to 70°F within two hours, it must be reheated to 165°F for 15 seconds. Following these guidelines will allow you to cook normally tough short ribs in an immersion circulator at 150°F for 48 hours, after which time the meat is tender, juicy and beautiful.

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