One of the most common ways humans contract foodborne illness is by eating foods that are undercooked. Foodborne-illness-causing microorganisms (pathogens) can easily contaminate food, and the only way to destroy these pathogens is to cook food to the proper internal temperature.

The food’s appearance is not a reliable measure for determining doneness. For example, meat can appear brown on the interior, but may have not reached the correct internal temperature to ensure safety. Alternatively, meat may appear pink in the center, but may actually be overcooked. The only way to ensure food is really done cooking is to use a food thermometer to verify the internal temperature of the food. By consistently using a thermometer, you can ensure your food is cooked to a safe temperature without being overcooked.

Types of thermometers

There is wide variation in the pricing and types of food thermometers available on the market. Some give near instantaneous readings while others must remain in the food for several minutes. The choice of which thermometer to use is based on personal preference and budget. Food thermometers can usually be purchased at your supermarket or home store. Below is a summary of some of the different types available, along with the pros and cons.

n Thermocouple — A thermocouple thermometer has a probe which is connected to a digital display by a wire. This type can give an accurate reading in two to five seconds, and is good for measuring the temperature of both thick and thin food. The probe does not need to be inserted very far into the food to give an accurate reading (usually one-quarter inch). This style can usually be calibrated. It is the costliest variety but is very easy to use.

n Thermistors — This thermometer provides a reading within 10 seconds on a digital display, but it must be inserted at least one-half inch into the food. Some models can be calibrated. This type is readily available in local home stores.

n Bimetallic-coil thermometers — this variety has a dial display which can sometime be difficult to read depending on the size of the display. Some varieties can be left inserted into the food while cooking while others cannot. You will need to check manufacturer’s instructions to ensure proper usage. The thermometers are not appropriate for use with thin foods, but are great for checking the temperature of roasts, casseroles, and soups. You will need to leave the thermometer inserted into the food for as long as two minutes to obtain an accurate reading. Additionally, the thermometer must be inserted into the food at least 2- 2 1/ 2” deep in the thickest part of the food. These models are more likely to give a false reading. Some models can be calibrated, while others cannot, so you will need to check manufacturer’s instructions.

n Instant read bimetallic-coil thermometers — These thermometers have nearly the same attributes as the bimetallic-coil thermometers above, but they cannot be left in food while cooking. Additionally, these thermometers will give an accurate reading within 15-20 seconds.

Calibrating thermometers and verifying accuracy

Some food thermometers can be calibrated, while others cannot. You will need to check the package insert for your particular brand and model to see if it can be calibrated, and for directions on how to calibrate the thermometer properly.

Regardless, a thermometer is not useful if it is not giving a correct reading. To ensure your thermometer is giving you an accurate reading, you should verify its accuracy. This can be done by filling a glass with ice, topping off with water, then inserting the thermometer into the glass. When checking the reading on the thermometer, the stem should not be touching the sides or bottom of the glass. The thermometer should read 32°F (±2°F).

You can also check the accuracy of the thermometer by immersing the stem in boiling water. The temperature should read 212°F; however, water boils at a lower temperature as altitude increases, so if you wish to use the boiling water method, please contact your local extension office for directions. If the thermometer is not within range, it should be recalibrated or a new thermometer should be purchased. Always check the accuracy of your thermometer if it has been dropped or experienced any other trauma.

Using a food thermometer

To ensure proper temperatures have been reached, and to prevent overcooking, check the internal temperature of the food toward the end of the anticipated cooking time. Always remove the food from the heat source prior to checking the temperature, and never leave the food thermometer inserted into the food during cooking.

Place the food thermometer in the center of the food to ensure the coldest portion of the food has reached the proper temperature. For meats, the thermometer needs to be inserted into the thickest part of the meat and should not be touching bone, fat, or gristle. Check the temperature of the food in several places to ensure it is evenly heated. Always clean your food thermometer with hot water and soap before and after each use.

For more information on using and selecting a food thermometer, please contact your local extension office.

If you have a food safety question you would like to see appear in this column, send your question to food.safety@wsu.edu.

Stephanie Smith is an assistant professor and statewide consumer food safety specialist for Washington State University Extension. She can be reached at food.safety@wsu.edu or at (855) 335-0575. Visit our website at extension.wsu.edu/foodsafety/. Follow us on Facebook at www.facebook.com/wsuextfs/ or on Twitter at www.twitter.com/WSU_foodsafety.

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