- The technology inside candy thermometers is no different from any other type. Ultimately, what makes a candy thermometer a candy thermometer is that it is programmed or labeled with the temperatures at which boiling sugar syrup reaches various physical stages. The hotter the syrup gets, the more firm it will be when it cools. Candy may recipes instruct cooks to add certain ingredients, lower cooking temperatures, or remove the liquid from heat when it has reached these stages.
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The most standard type of thermometer is a liquid-in-glass model. This thermometer consists of a sealed glass tube containing a liquid which rises when the bottom tip is heated. Since this expansion occurs at a predictable rate, temperature can be ascertained by use of a printed meter alongside the line of rising liquid.
Early liquid-in-glass thermometers were made with liquid mercury, but this practice was eventually banned due to the toxic nature of the material combined with the danger of glass thermometers bursting or breaking. Modern thermometers of this type, including all candy thermometers, are made using colored alcohol. Both kinds of liquid (mercury and alcohol) work according to the principles outlined above. - Coil spring thermometer technology is used in dial thermometers, devices which consist of a metal rod (the temperature sensor) attached to a disc-shaped top. Inside this part of the thermometer is a coil made up of two kinds of fused metal, usually copper and steel. One of these metals curls at a fast rate than the other when exposed to heat, while the other won't curl unless exposed to higher temperatures than the ones being measure. The non-curling metal is fixed inside the thermometer, while the faster-curling metal is attached to a mobile dial on the display face, which moves as the metal moves to indicate changes in temperature.
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Many modern candy thermometers are digital thermometers. Digital thermometers contain a temperature-measuring device known as a thermistor. A thermistor contains a type of semiconductor (a material which conducts electricity at an average rate) which can conduct greater electricity as it is exposed to higher heat. Thermistors can only be accurate within a narrow range of electrical activity, so digital thermometers are programmed for specific tasks, such as measuring body temperature, checking to see if cooked meat is hot enough, or recording the temperature of liquid candy.
This information is translated into a liquid crystal display, like those used for digital watches or calculators.
