Every kitchen should have a thermometer for food of some kind. Using a thermometer when cooking is the only sure way to know if an item has been cooked enough and is therefore safe for consumption. Higher temperatures kill bacteria that can exist in certain food items. In a commercial setting any food items that are held on a table such as a buffet line or salad bar, must be constantly monitored for safe holding temperatures on both cooked and chilled items.
Meat items must be cooked to a minimum temperature according to what type of meat it is. Poultry should be at least 160 degrees Fahrenheit throughout while port should be at least 170 degrees Fahrenheit. Diseases can be contracted from food items that are spoiled or not cooked enough. Salmonella will produce food poisoning and exists in all poultry products and some vegetables. Triconosis is a parasite that can live in undercooked pork.
Liquid Filled Thermometers
Liquid filled thermometers are glass tubes filled with colored liquid and a gauge for what temperature it is. Putting the thermometer in a liquid will raise the liquid in the thermometer to a certain level corresponding to what temperature the cooking liquid is. These are the oldest types of kitchen thermometers and are still used extensively for candy making. These cannot be inserted in meats for checking temperatures on cooked meat items. The temperature read can take a bit to come up to temp so these are mostly used to put in a liquid reading as you cook. Takes up to two minutes to read temperature.
A specialized candy or deep fry thermometer is able to withstand and read temperatures up to 400 degrees Fahrenheit.
These thermometers have a probe that has two types of metal in them that have different rates of expansion. The probe is inserted into the food item and an average temperature is derived from reading the temperature of the two metals. The temperature is taken at the first two inches of the probe from the tip to the dial.
Some of these thermometers can be oven save but check the documentation out first before you leave it in something in the oven. These are the traditional meat thermometers and have a larger dial to read in the oven without taking the food item out. These should never be used on items less than three inches thick.
Instant Read Thermometers
These can be any of the more modern types of thermometers and are designated by the fact that they read out a temperature in approximately 10 seconds. This is an important feature in a commercial setting when you have a certain time to get the food out to the customer once ordered.
Thermistor Style Thermometer
Thermistor style thermometers operate off of a ceramic resistor that is placed in the tip of a probe. These are instant read thermometers and usually have a digital temperature read out in a plastic housing. These are not to be left in the oven but are made to spot check items.
The thermocouple technology was born in the laboratory and is the fastest way to read the temperature of food items. Thermocouple thermometers are made with an interchangeable probe to be able to read internal or surface temperatures. The probe is very thin and can be used to measure temperatures of items thinner than most thermometers. The read out unit is usually a small box with a digital read out. These tend to be expensive as they are mostly made for industrial purposes but consumer models are now starting to appear.
Refrigerator and Oven Thermometers
These types of thermometers are used in either of the designated appliances and are made to be left in those appliances giving the ability to read the temperature at anytime.
Laser Infrared Thermometers
These are used to take the surface temperature of items without having to touch them or insert a probe. The light beam reads the temperature while the unit displays the temperature immediately in a digital read out. These are very expensive but are very handy to check pan temperature for different types of cooking or used to check the calibration of ovens.
Whatever type of kitchen thermometer you get to keep in your kitchen you will find many uses for it in your home. Feel and timing are good ways to test if you are close to being done on an item but the only true test is to take the temperature.