A cold water bath is a cooking technique that immediately arrests the process of whatever a person is cooking by directly immersing it in cold or even ice water. The simplest method is to pour cold water on foods like pasta while it still sits in the colander. This can help keep the pasta al dente for recipes like pasta salad. Placing food in cold water is also common when a cooks is blanching, or lightly cooking, vegetables for use as a side and in salads.
The reason chefs employ a cold water bath is because food that is heated will continue to cook slightly, even after it is removed from the heat. When a cook is minimally cooking food and needs it to retain a certain texture or firmness, he can still end up overcooking it if it's not cooled quickly. This may also be called shocking the food, since its result is to immediately end the cooking process.
Sometimes people add salt to the water, about 0.5 teaspoon (3 g) for every quart (liter) of water used. This can help the food retain its natural sodium, though many skip this step with fine results. The simple bath is composed of lots of ice covered in water. Some recipes recommend that cooks fill a bowl about two-thirds with ice, and then add enough water to cover it.
Food like blanched vegetables are then placed in the cold water bath and allowed to sit for a minute or two. They can then be removed and will not cook further. Cooks can store most vegetables that have been shocked for a few days in the refrigerator. They may want to consider placing them in airtight bags or lidded containers to keep them fresh. The vegetables should also be dried slightly if they will be stored, so that excess moisture does not ruin them.
This method should not be used for pasta when the cook plans to keep the food hot and serve it immediately. In fact, many recipes for pasta should not include a shock process, since even pouring cool water over pasta can remove the starchy coating pasta gets when it is cooking. This starch may be necessary when pasta is added directly to thin sauces, since it helps to thicken them. Similarly, if a cook is adding hot potatoes to thin sauces or soups to make them thicker, they should not be rinsed or shocked.