Food/Meat Thermometers—What You Need to Know

"It's safe to bite when the temperature is right"—that's the advice given by a USDA fact sheet on appliances and thermometers.  But how do you know when food is cooked to a sufficiently high temperature to kill the pathogens that cause food-borne illnesses?  An accurate food thermometer can tell you. "No modern kitchen should be without one," says our Advisory Board food process engineer, Dr. Timothy Bowser.  "Why do people take chances on risky methods of determining doneness of food when a thermometer will do the job better? It's like ignoring a perfectly good GPS or compass and relying on the wind, hearsay, memory, or a paper map written in a foreign language to find your way on an important mission over dangerous terrain."

That strong statement should convince you to go out and buy a food thermometer if you don't already have one.  They're easy to locate.  You can order one online, or find one for less than $10 at almost any hardware or big box store.  You can also spend hundreds on this product, but, according to Bowser, it isn't worth the cost.

I asked Dr. Bowser to tell us more about different ways that cooks test for doneness, different types of food thermometers, which features he prefers, and how to use the thermometer properly. Here are the Q/As:

What are some traditional but untrustworthy methods of determining doneness?

"When I stab it with a fork, the juices run clear, so it's done."  What's wrong with this method?  It may be done near the surface but not deep inside the poultry or roast. The fork method doesn't really account for cold spots deep in the food product. Cold spots can be caused by problems with thawing or densities of different materials like fat vs. muscle vs. stuffing vs. pockets of injected marinade.

"The little temperature indicator that came in the poultry/roast popped up, so  the food is done."  Not necessarily.  Those short probes don't get deep enough into the product to give you accurate information about doneness.

"I've cooked it as long as the recipe said to, so it must be done."  Not necessarily.  Your stove temperature, pan size, and amount of product may all be different from what the author of the recipe used.

"The hamburger is brown in the middle, so it's done."  According to the USDA fact sheet  "Why Use a Food Thermometer?" 1 out of every 4 hamburgers turns brown in the middle BEFORE it has reached a safe internal temperature. Though you may have used this method for years, color is NOT a reliable indicator of doneness.   

"My dinner guest, who's a very experienced cook, says it's done."  Your guest may be telling you what he/she thinks you want to hear.  Or, he/she may be very hungry!  At any rate, don't trust the so-called wisdom of others.  Trust only the thermometer.

What are the differences between the two main types of food thermometers— analog (dial) and digital?

When you stick the prong into your poultry, roast, or casserole the digital thermometer displays the temperature (in numerals); the analog has a dial with numerals and a pointer that moves around the dial until it reaches the temperature your food is at.

The digital thermometer will probably give you the temperature faster. The accuracy of a digital thermometer may be a little more or less than an analog thermometer, depending on the model and quality. Since I've needed bifocals, I've noticed that the digital ones are easier to read. For taking the temperature of thinner foods, the stem of the thermometer can be inserted parallel to the longest dimension of the food (for example, through the edge and into the middle of a hamburger patty).

The following explanation (from the website eHow) of how an analog thermometer works is a good one: "A meat thermometer takes advantage of the fact that different metals expand and contract at different temperatures. The rod of the meat thermometer contains two different metals that are bonded together. One expands at a lower temperature while the other must reach a higher temperature. The heat causes the strip of metal to bend or twist, depending on the temperature of the meat. The twisting metal triggers the dial and produces the readout on the display face of the meat thermometer."

A digital thermometer operates on batteries, which are used to power a sensor located in or near the tip of the probe. The sensor is normally a specialized integrated circuit chip, but can also be a thermocouple or a resistive temperature device. All of the sensors that are used in digital probes are designed to provide an electrical signal that is proportional to the temperature of its environment. The circuitry in the "brains" of the digital probe interprets the signal and sends the appropriate output to the digital display.

A digital thermometer should last quite a few years if handled carefully. I have owned digital thermometers that still worked well after 5 years.

Which brand and style of thermometer do you recommend?

Many of the inexpensive models do a great job.  For example, Taylor thermometers are known to be reliable and accurate.  Some of my favorites are made by Taylor (www.taylorusa.com).

The folding probe style is convenient.  It's like a pocket knife because it keeps the probe safely tucked away in a pocket or slot.  Some probes can be a bit sharp and therefore dangerous.  The tubular holders that generally come with these thermometers (and often have pocket clips on them) are hard to keep clean.

I especially like thermometers with thinner, sharper probes because they make a smaller hole, generally have a faster response time, and get a true temperature reading more quickly compared to other sensors.  An example of a good one is Taylor's 518 Connoisseur.  In my opinion, the Taylor model 518 and similar probes are one answer to the cleaning problem, while still making storage and use convenient.  To see this model online, click here: http://www.taylorusa.com/kitchen/thermometers/connoisseur-digital-cooking-thermometer-with-folding-probe.html

I can also recommend Taylor’s folding probe model 9306  It’s waterproof, includes an infrared non-contact thermometer, has a white light to illuminate the target, and a many other technical features that make it very attractive to the "food geek.” I think I should purchase one of these to try out myself!
http://www.taylorusa.com/kitchen/thermometers/waterproof-dual-temperature-thermocouple-and-infrared-thermometer.html

It seems as though Taylor has recognized the sleeve cleaning issue and addressed it in another fashion with their model 9848E  and some similar models (which I just found on their website). The 9848E has an antimicrobial sheath, a thin probe and it can be calibrated! The bright color is very visible and the readout is large. I haven't actually used one of these, but I do like the looks of it.  To see this one, click here: http://www.taylorusa.com/kitchen/thermometers/5-commercial-anti-microbial-instant-read.html

Some thermometers have a timer and an alarm function.  This timer might be useful for cooking as well as other kitchen chores. A chef may want to cook (or chill) a food to a certain temperature and then hold it at this temperature for a given time period.  For this function, the timer could be valuable.

How can I tell if my food thermometer is giving an accurate reading?

If it's a battery type, test the batteries to be sure they're working.  For either type, use the thermometer to measure the temperature of boiling water or an ice bath.  Here's how to do it:

The boiling point method: Immerse at least 2 inches of the probe in boiling water. If placed in boiling water, the thermometer should read 212°F (100°C). (At higher altitudes, the boiling point may be different. Check with your local health department if you're unsure about your area.) Allow a little time for the thermometer reading to adjust to its new environment. Then, if the temperature on your analog thermometer is not 212°F, rotate the thermometer head (with a wrench or pliers) until it reads 212°. Some models come with a calibrating wrench right on the case.  Follow the calibration instructions for your digital thermometer (if it is one of the models that can be calibrated).

The ice method: Set a cup of crushed ice aside, allow some of the ice to melt, and fill the voids. Insert the probe into this mixture. The temperature should stabilize at 32°F (0°C). (Water added to crushed ice does not stabilize as quickly and will not be as accurate as the "melting" method). If it doesn't read 32°F, an analog thermometer can be adjusted as described in the boiling point section above.

Remember, some digital thermometers cannot be recalibrated.  If one of this type becomes inaccurate, you have to buy another. 

What tips can you give on how to use the thermometer? 

Clean the probe before use and then insert it into the CENTER of the food product.  Probe in several places to identify the coolest location (when testing for doneness based on a high temperature requirement).  Temperatures may be cooler near areas of foods that were not thawed fully, are self-insulated (due to thickness of product, bones, skin, coating, etc.), are not exposed to the heat source and/or moving air, or are composed of different materials (e.g. stuffing in a bird).

That said, a thermometer isn't the best implement for testing the doneness of every food! I still recommend a pick or a toothpick to test the doneness of some baked goods. Visual inspection works very well on many items, such as cookies and biscuits.

How do I know what temperature to cook each type of food to?

For the Shelf Life Advice chart "Safe Temperatures for Cooking Food," click here:
http://shelflifeadvice.com/sites/default/files/pdf/SLA_FoodTempChart.pdf

For a USDA list "Temperature Rules," click here:
http://www.fsis.usda.gov/factsheets/Use_a_Food_Thermometer/index.asp

Note: The USDA has just recently reduced the safe minimum temperature for cooking pork from 160°F to 145°F. 

How many different kinds of food thermometers are there?

A lot. Here's a brief summary from the USDA that will answer this question more specifically:

Thermometers are turning up everywhere in today's kitchens in all shapes and sizes — digitals, instant-reads, probes for the oven and microwave, disposable indicators and sensor sticks, pop-ups, and even barbecue forks. They're high-tech and easy to use.

Some thermometers are meant to stay in the food while it's cooking; others are not. Some are ideal for checking thin foods, like the digital. Others, like the large-dial thermometer many people use, are really meant for large roasts and whole chickens and turkeys.

Choose and use the one that is right for you!

• Dial Instant-Read
• Digital Instant-Read
• Disposable Temperature Indicators
• Fork
• Dial Oven-Safe
• Pop-Up

Source(s):

Timothy J. Bowser, Ph.D. , Oklahoma State University, Dept. of Biosystems and Agricultural Engineering

Usda.gov Fact Sheets Appliances and Thermometers "Use a Food Thermometer"

http://www.fsis.usda.gov/factsheets/Use_a_Food_Thermometer/index.asp

EHow.com Food  "How Does a Meat Thermometer Work?"

http://www.ehow.com/how-does_4674342_meat-thermometer-work.html

taylorusa.com "Thermometers"

http://www.taylorusa.com/catalogsearch/result/?q=food+thermometer&x=9&y=11