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It is essential
to use a food thermometer when cooking meat, poultry, and egg
products to prevent undercooking, verify that food has
reached a safe minimum internal temperature, and consequently,
prevent foodborne illness.
Why Use a Food Thermometer?
Using a food thermometer is the only reliable way to ensure
safety and to determine desired "doneness" of meat,
poultry, and egg products. To be safe, these foods must be cooked
to a safe minimum internal temperature to destroy any harmful
microorganisms that may be in the food.
"Doneness" refers to when a food is cooked to
a desired state and indicates the sensory aspects of foods such
as texture, appearance, and juiciness. Unlike the temperatures
required for safety, these sensory aspects are subjective.
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Color is Not a Reliable Indicator
Many food handlers believe that visible indicators, such as
color changes, can be used to determine if foods are cooked
to a point where pathogens are killed. However, recent research
has shown that color and texture indicators are unreliable.
For example, ground beef may turn brown before it reaches a
temperature where pathogens are destroyed. A consumer preparing
hamburger patties and using the brown color as an indicator
of "doneness" is taking a chance that pathogenic microorganisms
may survive. A hamburger cooked to 160 °F as measured with a meat thermometer, regardless of
color, is safe.
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Safety Versus Doneness
The temperature at which different pathogenic microorganisms are destroyed varies, as does the "doneness" temperature for different meat and poultry. A consumer looking for a visual sign of "doneness" might continue cooking it until it is overcooked and dry. However, a consumer using a food thermometer to check for "doneness" can feel assured the food has reached a safe temperature and is not overcooked. Cook all raw beef, pork, lamb and veal steaks, chops, and roasts to a minimum internal temperature of 145°F as measured with a food thermometer before removing meat from the heat source. For safety and quality, allow meat to rest for at least three minutes before carving or consuming. For reasons of personal preference, consumers may choose to cook meat to higher temperatures.
Cook all poultry to a safe minumum internal temperature of 165 °F as measured with a food thermometer. For reasons of personal preference, consumers may choose to cook meat to higher temperatures.
A food thermometer should also be used to ensure that cooked
food is held at safe temperatures until served. Cold foods should
be held at 40 °F or below. Hot food should be kept hot at
140 °F or above.
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Types of Thermometers
Food thermometers come in several types and styles, and vary
in level of technology and price.
Digital Food Thermometers
Thermocouple:
Of all food thermometers, thermocouple thermometers reach and
display the final temperature the fastest – within 2 to
5 seconds. The temperature is indicated on a digital display.
A thermocouple measures temperature at the junction of two fine
wires located in the tip of the probe. Thermocouples used in
scientific laboratories have very thin probes, similar to hypodermic
needles, while others may have a thickness of 1/16 of an inch.
Since thermocouple thermometers respond so rapidly, the temperature
can be quickly checked in a number of locations to ensure that
the food is safely cooked. This is especially useful for cooking
large foods, such as roasts or turkeys, when checking the temperature
in more than one place is advised. The thin probe of the thermocouple
also enables it to accurately read the temperature of thin foods
such as hamburger patties, pork chops, and chicken breasts.
Thermocouples are not designed to remain in the food while it's
cooking. They should be used near the end of the estimated cooking
time to check for final cooking temperatures. To prevent overcooking,
check the temperature before the food is expected to finish
cooking.
Thermocouples can be calibrated for accuracy.
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Thermistors:
Thermistor-style food thermometers use a resistor (a ceramic
semiconductor bonded in the tip with temperature-sensitive epoxy)
to measure temperature. The thickness of the probe is approximately
1/8 of an inch and takes roughly 10 seconds to register the
temperature on the digital display. Since the semiconductor
is in the tip, thermistors can measure temperature in thin foods,
as well as thick foods. Because the center of a food is usually
cooler than the outer surface, place the tip in the center of
the thickest part of the food.
Thermistors are not designed to remain in the food while it's
cooking. They should be used near the end of the estimated cooking
time to check for final cooking temperatures. To prevent overcooking,
check the temperature before the food is expected to finish
cooking.
Not all thermistors can be calibrated. Check the manufacturer's
instructions.
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Oven Cord Thermometers:
This food thermometer allows the cook to check the temperature
of food in the oven without opening the oven door. A base unit
with a digital screen is attached to a thermistor-type food
thermometer probe by a long metal cord. The probe is inserted
into the food, and the cord extends from the oven to the base
unit. The base can be placed on the counter or attached to the
stovetop or oven door by a magnet. The thermometer is programmed
for the desired temperature and beeps when it is reached. While
designed for use in ovens, these thermometers can also be used
to check foods cooking on the stove. Oven cord thermometers
cannot be calibrated.
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Thermometer Fork Combination:
This utensil combines a cooking fork with a food thermometer.
A temperature-sensing device is embedded in one of the tines
of the fork. There are several different brands and styles of
thermometer forks on the market; some using thermocouples and
some using thermistors. The food temperature is indicated on
a digital display or by indicator lights on the handle within
2 to 10 seconds (depending on the type). These lights will tell
if the food has reached rare, medium, well done, etc. Particularly
useful for grilling, the thermometer fork will accurately measure
the internal temperature of even the thinnest foods. The thermometer
fork should be used to check the temperature of a food towards
the end of the estimated cooking time. Thermometer forks are
not designed to remain in a food while in the oven or on the
grill. Thermometer forks cannot be calibrated.
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Dial Food Thermometers
Bimetallic-coil
Thermometers:
These thermometers contain a coil in the probe made of two different
metals that are bonded together. The two metals have different
rates of expansion. The coil, which is connected to the temperature
indicator, expands when heated. This food thermometer senses
temperature from its tip and up the stem for 2 to 2 1/2 inches.
The resulting temperature is an average of the temperatures
along the sensing area. These food thermometers have a dial
display and are available as "oven-safe" and "instant-read."
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"Oven-safe" Bimetallic-coil Thermometers:
This food thermometer is designed to remain in the food while
it is cooking in the oven, and is generally used for large items
such as a roast or turkey. This food thermometer is convenient
because it constantly shows the temperature of the food while
it is cooking. However, if not left in the food while cooking,
they can take as long as 1 to 2 minutes to register the correct
temperature.
The bimetal food thermometer can accurately measure the temperature
of relatively thick foods (such as beef roasts) or deep foods
(foods in a stockpot). Because the temperature-sensing coil
on the stem is between 2 to 2 1/2 inches long and the stem is
relatively thick, it is not appropriate to measure the temperature
of any food less than 3 inches thick.
There is concern that because heat conducts along the stem's
metal surface faster than through the food, the area of the
food in contact with the thermometer tip will be hotter than
the area a short distance to the side (the "potato nail
effect"). To remedy this, the temperature should be taken
in a second, and even third area, to verify the temperature
of the food. Each time the thermometer is inserted into the
food, let the thermometer equilibrate (come to temperature)
at least 1 minute before reading the temperature.
Some models can be calibrated. Check the manufacturer's instructions.
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"Instant Read" Bimetallic-coil Thermometers:
This food thermometer quickly measures the temperature of a
food in about 15 to 20 seconds. It is not designed to remain
in the food while it is cooking in the oven, but should be used
near the end of the estimated cooking time to check for final
cooking temperatures. To prevent overcooking, check the temperature
before the food is expected to finish cooking.
For accurate temperature measurement, the probe of the bimetallic-coil
thermometer must be inserted the full length of the sensing
area (usually 2 to 3 inches). If measuring the temperature of
a thin food, such as a hamburger patty or boneless chicken breast,
the probe should be inserted through the side of the food so
that the entire sensing area is positioned through the center
of the food. Some models can be calibrated. Check the manufacturer's
instructions.
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Single-Use Temperature Indicators
One of the most recent developments in the retail food market
is the emergence of disposable temperature indicators. Several
brands are available, and all make quick work of determining
if a food has reached its final temperature. These temperature
sensors are designed for specific temperature ranges, for example,
160-170 °F. It is important that the sensors be used only
with foods for which they are intended. Read the package directions
to ensure that the temperature the sensor will reach is consistent
with the safe temperatures listed in this publication.
The sensors are made from special temperature-sensitive materials.
The sensor is inserted into a food. When the food reaches the
safe temperature, the sensor changes color. They are designed
to be used only once. However, if the desired temperature has
not been reached, they can be reinserted until the temperature
is reached. These sensors cannot be left in a food while it
is cooking. They should be used near the end of the estimated
cooking time. To prevent overcooking, check the temperature
before the food is expected to finish cooking.
Disposable temperature indicators are made from materials approved
by the FDA for contact with food.
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Pop-Up Timers:
Commonly used in turkeys and roasting chickens since 1965, the
"pop-up" style disposable cooking device is constructed
from a food grade nylon. The inside contains a stainless steel
spring and organic firing material. The organic firing material
is specifically designed to dissolve at specific predetermined
temperatures. Once the firing material dissolves, the stainless
steel spring releases the stem, allowing it to "pop up."
This indicates that the food has reached the correct final temperature
for safety and doneness. Pop-up style disposable cooking devices
are reliable to within 1 to 2 °F, however, proper placement
is important. Checking with a conventional food thermometer
is always recommended as an added precaution to properly gauging
both safety and doneness.
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Other Types of Food Thermometers
Liquid-filled Thermometers:
Also called "spirit-filled" or "liquid in glass"
thermometers, these thermometers are the oldest kind of food
thermometer used in home kitchens. They have either metal or
glass stems. As the internal temperature of the food increases,
the colored liquid inside the stem expands and rises to indicate
the temperature on a scale. Heat conduction in the metal stems
can cause false high readings. They are designed to remain in
the food while it is cooking. They should be inserted at least
2 inches deep in the thickest part of the food, and are, therefore,
not appropriate for thin foods. Some liquid-filled thermometers
can be calibrated by carefully moving the glass stem within
the holder.
Candy/Jelly/Deep Fry Thermometers:
These thermometers will measure temperatures ranging from 100
to 400 °F. They are used to measure the extra-high temperatures
required of candy and jelly making, as well as frying with hot
oil.
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Appliance Thermometers
Refrigerator/
Freezer Thermometers:
For safety, it is important to verify the temperature of refrigerators
and freezers. Refrigerators should maintain a temperature of
40 °F or below. Frozen food will hold its top quality for
the longest possible time when the freezer maintains 0 °F
or below. An appliance thermometer can be kept in the refrigerator
and freezer to monitor the temperature. This can be critical
in the event of a power outage. When the power goes back on,
if the refrigerator is 40 °F or below, and the freezer is
still colder than 40 °F, the food is safe. These bimetallic-coil
thermometers are specially designed to provide accuracy at cold
temperatures.
Oven Thermometers:
An oven thermometer can be left in the oven to verify that the
oven is heating to the desired temperatures. These bimetallic-coil
thermometers can measure temperatures from 100 to 600 °F.
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Food Thermometers |
| Types |
Speed |
Placement |
Usage
Considerations |
| Digital
Thermometers |
| Thermocouple |
2-5
seconds |
1/4"
or deeper in the food, as needed |
•
Gives fastest reading
• Good for measuring
temperatures of thick and thin foods
• Not
designed to remain in food while it's cooking
•
Check internal temperature of food near the end of cooking
time
• Can be calibrated
• More
costly; may be difficult for consumers to find in stores
|
| Thermistor |
10
seconds |
At
least 1/2" deep in the food |
•
Gives fast reading
• Can measure temperature
in thin and thick foods
• Not designed to remain
in food while it's cooking
• Check internal
temperature of food near the end of cooking time
• Some models can be calibrated; check manufacturer's
instructions
• Available in "kitchen"
stores
|
| Oven Cord Thermometer |
10
seconds |
At
least 1/2" deep in the food |
•
Can be used in most foods
• Can also be used
outside the oven
• Designed to remain in the
food while it is cooking in oven or in covered pot
• Base unit sits on stovetop or counter
•
Cannot be calibrated
|
| Thermometer Fork
Combination |
2-10
seconds |
At
least 1/4" in the thickest part of food |
•
Can be used in most foods
• Not designed to
remain in food while it is cooking
• Sensor
in tine of fork must be fully inserted
• Check
internal temperature of food near the end of cooking time
• Cannot be calibrated
• Convenient
for grilling
|
| Dial
Thermometers |
| Oven-Safe, Bimetal
|
1-
2 minutes |
2-2
1/2" deep in the thickest part of the food |
•
Can be used in roasts, casseroles, and soups
•
Not appropriate for thin foods
• Can remain
in food while it's cooking
• Heat conduction
of metal stem can cause false high reading
•
Some models can be calibrated; check manufacturer's instructions
|
| Instant-Read,
Bimetal |
15-
20 seconds |
2-2
1/2" deep in the thickest part of the food |
•
Can be used in roasts, casseroles, and soups
• Temperature is averaged along probe, from tip
to 2-3" up the stem
• Cannot measure thin foods unless
inserted sideways
• Not designed to remain
in food while it is cooking
• Use to check
the internal temperature of a food at the end of cooking
time
• Some models can be calibrated; check
manufacturer's instructions
• Readily available
in stores
|
| Other
|
| Single-Use Temperature
Indicators |
5-10
seconds |
Approx.
1/2" deep (follow manu- facturer's directions) |
•
Designed to be used only once
• Designed for
specific temperature ranges
• Should only be
used with food for which they are intended
•
Temperature- sensitive material changes color when the
desired temperature is reached
|
Liquid-Filled
(glass or
metal stem) |
1-2
minutes |
At
least 2" deep in the thickest part of the food |
•
Used in roasts, casseroles, and soups
• Can
remain in food while it's cooking
• Cannot
measure thin foods
• Some can be calibrated;
check manufacturer's instructions
• Possible
breakage of glass stem while in food
• Heat
conduction of metal stem can cause false high reading
|
|
[Top of Page]
Safety and Doneness
Most pathogens are destroyed between 140 and 165 °F. Higher
temperatures may be necessary to achieve consumer acceptability
and palatability, also known as "doneness."
These temperatures are recommended for consumer cooking. They
are not intended for processing, institutional, or foodservice
preparation. Food service professionals should consult their
state or local food code.
|
|
Recommended Internal
Temperatures * |
| Food
|
°F |
| Ground
Meat & Meat Mixtures |
| Beef, Pork, Veal,
Lamb |
160 |
| Turkey, Chicken
|
165 |
| Fresh
Beef, Pork, Veal, Lamb |
| Beef, Pork, Veal, & Lamb (steaks, roasts and chops) |
145** |
| **as measured with a food thermometer before removing meat from the heat source. For safety and quality, allow meat to rest for at least three minutes before carving or consuming. For reasons of personal preference, consumers may choose to cook meat to higher temperatures. |
| Ham |
| Fresh (raw) or “cook-before-eating” |
145** |
| Pre-cooked (to reheat) |
140 |
| Poultry |
| Chicken, Turkey, Duck & Goose (whole or pieces) |
165 |
| Poultry breasts,
roasts |
165 |
| Stuffing (cooked
alone or in bird) |
165 |
| Eggs
and Egg Dishes |
| Eggs |
Cook until yolk
and white are firm |
| Egg dishes |
160 |
| Leftovers
and Casseroles |
165 |
|
*These temperatures are recommended for consumer cooking. They are not intended for processing, institutional, or foodservice preparation. Food service professionals should consult their state or local food code.
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Using the Food Thermometer
Most available food thermometers will give an accurate reading
within 2 to 4 °F. The reading will only be correct, however,
if the thermometer is placed in the proper location in the food.
If not inserted correctly, or if the food thermometer is placed
in the wrong area, the reading will not accurately reflect the
internal temperature of the food. In general, the food thermometer
should be placed in the thickest part of the food, away from
bone, fat, or gristle.
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Check Manufacturer's Instructions
Before using a food thermometer, read the manufacturer's instructions
first. The instructions should tell how far the thermometer
must be inserted in a food to give an accurate reading. If instructions
are not available, check the stem of the food thermometer for
an indentation, or "dimple." This shows one end of
the location of the sensing device. Dial thermometers must penetrate
about 2 to 3 inches into the food. Most digital thermometers
will read the temperature in a small area of the tip.
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Where to Place the Food Thermometer
Meat
When taking the temperature of beef, pork, or lamb roasts, the
food thermometer should be placed midway in the roast, avoiding
the bone. When cooking hamburgers, steaks, or chops, insert
a thermistor or thermocouple in the thickest part, away from
bone, fat, or gristle. If using a dial bimetal thermometer,
read "Thin Foods" below.
When the food being cooked is irregularly shaped, such as with
a beef roast, check the temperature in several places.
Poultry
FSIS recommends cooking whole poultry to a safe minimum internal
temperature of 165 °F as measured with a food thermometer.
For reasons
of personal preference, consumers may choose to cook poultry
to higher temperatures. Check the internal temperature in the innermost part of the
thigh and wing and the thickest part of the breast. For optimum safety, do not stuff poultry.
If stuffing whole poultry, the center of the stuffing must reach
a safe minimum internal temperature of 165 °F. If cooking
poultry parts, insert food thermometer into the thickest area,
avoiding the bone. The food thermometer may be inserted sideways
if necessary. When the food is irregularly shaped, the temperature
should be checked in several places.
Thin Foods
When measuring the temperature of a thin food, such as a hamburger
patty, pork chop, or chicken breast, a thermistor or thermocouple
food thermometer should be used, if possible.
However, if using an "instant-read" dial bimetallic-coil
food thermometer, the probe must be inserted in the side of
the food so the entire sensing area (usually 2-3 inches) is
positioned through the center of the food.
To avoid burning fingers, it may be helpful to remove the food
from the heat source (if cooking on a grill or in a frying pan)
and insert the food thermometer sideways after placing the item
on a clean spatula or plate.
Combination Dishes
For casseroles and other combination dishes, place the food
thermometer into the thickest portion of the food or the center
of the dish. Egg dishes and dishes containing ground meat and
poultry should be checked in several places.
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Thermometer Care
As with any cooking utensil, food thermometers should be washed
with hot soapy water. Most thermometers should not be immersed
in water. Wash carefully by hand.
Use caution when using a food thermometer. Some models have
plastic faces, which can melt if placed too close to heat or
dropped in hot liquid.
Thermometer probes are sharp and should be stored with the
probe in the stem sheath. Some glass thermometers are sensitive
to rough handling and should be stored in their packaging for
extra protection or in a location where they will not be jostled.
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Calibrating a Thermometer
There are two ways to check the accuracy of a food thermometer.
One method uses ice water, the other uses boiling water. Many
food thermometers have a calibration nut under the dial that
can be adjusted. Check the package for instructions.
Ice Water
To use the ice water method, fill a large glass with finely
crushed ice. Add clean tap water to the top of the ice and stir
well. Immerse the food thermometer stem a minimum of 2 inches
into the mixture, touching neither the sides nor the bottom
of the glass. Wait a minimum of 30 seconds before adjusting.
(For ease in handling, the stem of the food thermometer can
be placed through the clip section of the stem sheath and, holding
the sheath horizontally, lowered into the water.) Without removing
the stem from the ice, hold the adjusting nut under the head
of the thermometer with a suitable tool and turn the head so
the pointer reads 32 °F.
Boiling Water
To use the boiling water method, bring a pot of clean tap water
to a full rolling boil. Immerse the stem of a food thermometer
in boiling water a minimum of 2 inches and wait at least 30
seconds. (For ease in handling, the stem of the food thermometer
can be placed through the clip section of the stem sheath and,
holding the sheath horizontally, lowered into the boiling water.)
Without removing the stem from the pan, hold the adjusting nut
under the head of the food thermometer with a suitable tool
and turn the head so the thermometer reads 212 °F.
For true accuracy, distilled water must be used and the atmospheric
pressure must be one atmosphere (29.921 inches of mercury).
A consumer using tap water in unknown atmospheric conditions
would probably not measure water boiling at 212 °F. Most
likely it would boil at least 2 °F, and perhaps as much
as 5 °F, lower. Remember that water boils at a lower temperature
in a high altitude area. Check with the local Cooperative Extension
Service or Health Department for the exact temperature of boiling
water.
Even if the food thermometer cannot be calibrated, it should
still be checked for accuracy using either method. Any inaccuracies
can be taken into consideration when using the food thermometer,
or the food thermometer can be replaced. For example, water
boils at 212 °F. If the food thermometer reads 214 °F
in boiling water, it is reading 2 degrees too high. Therefore
2 degrees must be subtracted from the temperature displayed
when taking a reading in food to find out the true temperature.
In another example, for safety, ground beef patties must reach
160 °F. If the thermometer is reading 2 degrees too high,
2 degrees would be added to the desired temperature, meaning
hamburger patties must be cooked to 162 °F.
"Is it done yet?" You
can't tell by looking. Use a food
thermometer to be sure.
www.IsItDoneYet.gov
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Last Modified:
June 9, 2011 |
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