Before chefs rediscovered the possibilities of cooking with hot-water baths, immersion circulators were already around. They're important tools for scientists such as biologists and chemists, who sometimes need to keep samples at specific temperatures.
A basic immersion circulator has the following parts:
- a tube
- a pump
- a heating element
- a thermometer
- a set of control circuits
- an interface
Here's how it works. First, you place the immersion circulator so that the heating element and tube are immersed in water. The control unit remains out of the water, typically perched on the edge of the container you're using. Then, you must provide power to the immersion circulator, typically by plugging it in to an outlet. You set the temperature you require for your hot-water bath using the interface. Each type of food requires a different temperature and cooking time. The control circuitry switches on power to the heating element, such as a set of coils that convert electricity into heat.
Constant circulation keeps the water at uniform temperature throughout the container. To do that, a pump pulls water into the mouth of a tube located at the base of the circulator. Water emerges from the top of the tube, which may or may not also be submerged in the water.
The thermometer monitors the water's temperature and relays that information to the control circuit. When the water begins to cool, the control circuitry activates the heating element, warming the water. When the water is at the desired temperature, the control circuitry switches the heating element off. The water will continue to circulate through the tube.
A good immersion circulator maintains a water bath's temperature to within a few hundredths of a degree. This precision is necessary for cooks who want a specific outcome with their dishes. After the prescribed cooking time completes, you remove the bags from the hot water bath and finish the dish with seasoning or other preparation methods -- such as searing -- and serve.