Since a major aspect of cooking is the heating of ingredients, temperature is an
important topic. In cooking, we are primarily concerned in the temperature of our
cooking environment (such as deep frying oil) and the temperature of our food (like
a roast). With some foods, if the temperature of an ingredient has passed a certain
point, it's texture and flavor changes such that we call it overdone. With other
dishes, like pot roast, a minimum temperature must be reached to produce the desired
effect. With lean steaks and roasts, there is a very small window which enables
us to serve the dish as the perfect temperature. A thermometer is an invaluable
tool in the kitchen
Mechanical or dial thermometers
Mechanical or dial thermometer uses two strips of different metal bonded together.
The different metals have dissimilar expansion rates as temperature increases. Because
of this, the bimetallic strip curls when the temperature changes. When constructed
in the shape of a coil, the curling metal can be used to alter the angle of a needle.
A dial thermometer is constructed by placing the needle in front of a static background
and marking the background with known temperatures.
Bulb thermometers are based on the expansion of liquids. A liquid is encased in
a thin transparent tube with a small reservoir at one end. As the liquid in the
reservoir expands or contracts due to temperature change, the level of the liquid
in the tube also changes. The thermometer is read by matching the level of the liquid
with markings that label known temperatures. Mercury is a common liquid used in
bulb thermometers, but should not be used in the kitchen because mercury is a poison
and unsafe if the thermometer is broken. Most bulb thermometers for kitchen use
are filled with an alcohol (stained red for easy reading).
Electronic or digital thermometers (infared thermometers)
Electronic or digital thermometers operate based on an electronic component that
reacts to different temperatures. Most digital kitchen thermometers use a thermistor
(thermoresistor) - a device whose resistance changes due to temperature. When a
current is passed through the thermistor, a voltage drop occurs. This voltage can
be measured and a small microcomputer calculates the temperature based on the voltage.
The temperature is then displayed for the user to read. Another technique, is to
take advantage of the principle that joining two different metals causes a voltage
potential between them that is dependent on the temperature of the junction.
What to buy?
If you only have space for one thermometer you must have a "Probe" type thermometer.
This thermometer has to be fast, acurate and to mesure a wide temperature range.
It also have to be easy to use and read