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One of the critical factors in controlling bacteria in food
is controlling temperature. Pathogenic microorganisms grow very
slowly at temperatures below 40 °F, multiply rapidly between
40 and 140 °F, and are destroyed at temperatures above 140
°F. For safety, foods must be held at proper cold temperatures
in refrigerators or freezers and they must be cooked thoroughly.
But how would a consumer know if the refrigerator was cold enough,
or if the oven was heating at the proper temperature?
Appliance thermometers are specially designed to measure the
temperature of the air in either the refrigerator/freezer or
the oven. Some refrigerator thermometers have long metal probes
and are similar in appearance to food thermometers. Other refrigerator
thermometers, and most oven thermometers, are designed to hang
from a wire rack or sit on a shelf.
Whether they measure the temperature in the oven or refrigerator/freezer,
most appliance thermometers are either liquid-filled or bimetallic-coil
thermometers:
- Liquid-filled Thermometers, also called
"spirit-filled" or "liquid in glass" thermometers, are the
oldest types of thermometers used in home kitchens. As the
temperature increases, the colored liquid (usually an alcohol
solution) inside the thermometer expands and rises to indicate
the temperature on a scale.
- Bimetallic-coil Thermometers contain
a coil made of 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. As the temperature increases, the pointer
will be rotated by the coiled bimetal element to indicate
the temperature.
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Using Appliance Thermometers
Refrigerator/Freezer Thermometers
Refrigerator/freezer thermometers are specially designed to
provide accuracy at cold temperatures.
For safety, it is important to verify the temperature of refrigerators
and freezers. Refrigerators should maintain a temperature no
higher than 40 °F. Frozen food will hold its top quality
for the longest possible time when the freezer maintains 0 °F.
Most refrigerators and freezers can be easily adjusted to run
colder or warmer. The temperature control is usually accessible
in the refrigerator part of the appliance. Check the owner’s
manual for specific details on adjusting the temperature. An
adjustment period is often required when changing the temperature.
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To measure the temperature in the refrigerator:
Put the thermometer in a glass of water and place in the middle
of the refrigerator. Wait 5 to 8 hours. If the temperature is
not 38 to 40 °F, adjust the refrigerator temperature control.
Check again after 5 to 8 hours.
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To measure the temperature in the freezer:
Place the thermometer between frozen food packages. Wait 5 to
8 hours. If the temperature is not 0 to 2 °F, adjust the
freezer temperature control. Check again after 5 to 8 hours.
An appliance thermometer can be kept in the refrigerator and
freezer to monitor the temperature at all times. This can be
critical in the event of a power outage. When the power goes
back on, if the refrigerator is still 40 °F and the freezer
is 0 °F or below, the food is safe.
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Oven Thermometers
An oven thermometer can be left in the oven to verify that the
oven is heating to the desired temperatures. When cooking meat
and poultry, it is important that the oven be set at 325 °F
or higher. These thermometers can measure temperatures from
100 to 600 °F.
To check the accuracy of an oven, hang the oven thermometer
from a rack in the center of the oven (you may have to adjust
the oven racks). Set the oven for 325 to 350 °F and allow
it to preheat. Once the oven has reached the set temperature,
open the oven door and read the thermometer. The oven maintains
its temperature by cycling on and off, especially if the door
has been opened. Check the temperature again after 5 minutes.
If the oven is not maintaining the set temperature, the oven
thermostat will have to be adjusted by a service center representative
authorized by the manufacturer. However, if, after testing the
oven temperature at several settings (325, 350, 375, and 400
°F), it is consistently high or low by the same amount (say,
25 °F), this can be factored into the temperature setting.
For example, if you know that your oven runs "hot" by 25 °F
and you need to bake something at 350 °F, set the oven for
325 °F. Always check the oven thermometer to verify the
temperature.
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Microwave Oven Probes
A microwave oven probe can be plugged into the microwave and
inserted in the food being cooked. Some microwaves can be programmed
to cook the food until a desired temperature is reached. Check
the owner’s manual for more information. Some thermometers
are specially designed to be used in the microwave oven, but
most food thermometers are not microwave-safe. Check the packaging
instructions for more information.
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Last Modified:
October 6, 2008 |
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