They can take as long as 1 to 2 minutes to register the correct temperature. The bimetal stem thermometer can accurately measure the temperature of relatively thick or deep foods such as beef roasts and foods in a stockpot. There is concern, however, that because heat conducts along the stem's metal surface faster than through the food, the food in contact with the thermometer tip will be hotter than the food a short distance to the side. To remedy this, the temperature should be taken in a second and even third place to verify the temperature of the food. Each time the thermometer is inserted into a food let the temperature equilibrate, or come to temperature, at least 1 minute before reading the temperature.
Food thermometers come in several types and styles and range in level of technology and price.
These thermometers are designed to quickly measure the temperature and cannot be left in the oven while the food is cooking. About 15 to 20 seconds are required for the temperature to be accurately displayed on a dial. The thermometer is inserted in the food only while assessing the temperature. Once the temperature is determined, the thermometer must be removed. It is important to wash the probe with hot, soapy water after each insertion to prevent cross-contamination.