An ice bath, a simple combination of water and ice, is used to rapidly stop the cooking process, chill beverages, and to increase food safety. This technique is especially valuable when blanching and parboiling ingredients, working with eggs cooked in their shell, and custards. The process of placing food directly in the ice water is known as shocking. To properly follow food safety guidelines, you need to quickly chill hot foods like soups and stocks that you are planning to portion and store prior to moving them to a refrigerator or freezer to prevent bacteria formation. This rapid reduction in temperature keeps the food from remaining in the danger zone for long periods of time, which reduces bacteria from multiplying. Cooked food should not remain in the danger zone, 140° F (60° C) to 40° F (4° C), for more than two hours. This temperature range provides the optimum breeding ground for bacteria that lead to food-borne illnesses. As a result, cooling food at room temperature or moving hot food to a container and placing it in a freezer or refrigerator are not adequate preventative measures. The reasons are two-fold: first, a freezer or refrigerator may not move the food temperature below the danger zone within two-hours, secondly, the temperature of the food will not be even and food in the center of the container remains in the danger zone longer and can breed bacteria.
When using an ice bath prepare it by filling a large bowl with ice just before you need it, preferably metal as it chills more rapidly than glass or plastic. Add enough cold water so the ice is not sticking together and flows around the object you are placing in the bath, but not so much that the water overflows once you place it in the container. When using an ice bath to cool a sauce or custard from another bowl, make sure you use a container with a large enough size that you have a good flow between the two vessels, this allows cooling from the sides and bottom. Be prepared to add additional ice to the mixture through the cooling process or to drain some melt and add more ice as needed.
When shocking small pieces of food like vegetables, use a slotted spoon to transfer the food into and out of the ice bath or nest a colander in the ice bath, which makes for easier removal. Some chefs add several tablespoons of salt to an ice bath, which causes the mixture’s temperature to drop and slows the ice melting. Just keep in mind that, depending on your technique, the food can come in contact with the ice, salt, and water mixture. If you wish to use salt and want to avoid this contact, make sure you opt to cool that food in a pan or bowl and use the nesting technique as described. When the food reaches 40° F (4° C), it is safe to move it to the freezer or refrigerator for storage.