The most reliable thermometers available today have a 'bulb,' a glass column that encases alcohol-based or spirit-based material, and is not affected by external conditions. It will give you accurate readings until it breaks. Take care to store these, and all, thermometers, where they cannot be jostled, so that the liquid doesn't separate; ideally hanging them upright, if you can.
Dial thermometers generally use either bi-therm metals or a spring. Bi-therm stem thermometers comprise two or more metals that expand at different rates with temperature changes, causing the dial to turn when expansion and contraction occur. Spring thermometers have an actual spring, which similarly expands and contracts, causing the dial to turn. Of the two, bi-therm thermometers are more reliable, and can usually be re-calibrated.
Digital thermometers have a little computer that measures electrical resistance created by changes in temperature at the sensor, and readings are usually very accurate. Degradation of the resistor over time causes it to lose accuracy, however many can be re-calibrated.
Oven thermometers should be a part of every kitchen. Unless you have your oven recalibrated annually, chances are good that the actual temperature will differ from the oven settings you choose. And that will affect every food you cook in your oven.
Today, the most commonly used general purpose thermometers are called 'instant read,' because they give you an accurate reading in just a few seconds for digital ones, to about 30 seconds for ones with dials. The probe must be inserted past a marked point, usually about 1 in. or so, and their accuracy rate is +/-3°F, which is generally acceptable.
Instant read thermometers need to be adjusted from time to time. Insert the probe in boiling water (212°F at sea level), and adjust (after cooling down to room temperature) accordingly. There's a handy screw under the head for just that purpose on dial thermometers, and many electronic thermometers can also be adjusted.
Use the pocket clip to store the thermometer in your apron or shirt pocket, so it's always within easy reach. And use the the circular hook on the pocket case to insert the probe into, so your hands can stay safely away from hot, splattering foods.
Meat thermometers have a limited temperature range, specifically for the indication of internal temperature of the meat. Attaining the correct temperature is essential to kill off potential pathogens.
Candy, jelly and deep fry are lumped together because of the temperature range required for these foodstuffs. A correct temperature is crucial. Remember good safety habits when dealing with these and other hot foods.
If the fridge or freezer are not maintained at the correct temperatures, spoilage can occur easily. The freezer should be kept between 0 and -10°F, and the fridge between 34 and 40°F.
Position a thermometer's probe away from materials that can affect the temperature reading, but not the temperature of the substance being measured. Like bone, for example, or the side of a pot.
Infrared surface thermometers measure the temperature of a surface. You can easily check the temperature of your fry pan for the optimum time to add food (about 400°F), the food in your fridge or freezer, or even in the supermarket or on the table. The one we offer has a laser sighting, so you'll always aim correctly, and it never touches the surface, so it stays clean. (You can also use it to measure your car engine's temperature, or from windows, walls, heating and air conditioning grills, etc.)