Controlling temperature is one of the
critical factors in controlling bacteria in food. At temperatures below
40 degrees F, pathogenic microorganisms grow very slowly but multiply
very rapidly at between 40 and 140 degrees F. At temperatures above 140
degrees F, they are destroyed. So to ensure that food are safe for
consumption, it must be stored at proper cold temperatures in
refrigerators or freezers and also must be cooked thoroughly. But how
would you know if the refrigerator is cold enough or the oven is
actually heating at the proper temperature?
Appliance thermometers are specially
designed to measure the air temperature of either the refrigerator or
the oven. Similar in appearance with the food thermometers, some
refrigerator thermometers also have long metal probes while some are
designed to hang from a wire rack or sit on a shelf. Most appliance
thermometers are either liquid-filled thermometers or bimetallic-coil
thermometers irregardless of whether they are used to measure
temperature in the refrigerator, freezer or the oven.
The oldest types of thermometers used in
home kitchens are the liquid-filled thermometers which are also known as
"spirit-filled" or "liquid in glass" thermometers. The colored liquid
inside the thermometer will expands and rises to indicate the
temperature on a scale as the temperature increases.
As for the bimetallic-coil thermometers,
they contain a coil made from two different metals with different rates
of expansion that are bonded together. The bimetal element is coiled,
fixed at one end, and attached to a pointer stem at the other end. The
pointer will be rotated by the coiled bimetal element to indicate the
temperature as the temperature increases.