Deep Fry Thermometers

Monday, 4 May 2009 | Tags: ,

When making candy or deep frying, cooking at the correct temperature is an important factor. But not any old thermometer will do. A deep fry thermometer is designed to withstand the intense heat of these cooking methods, so we find out if one works better than the rest.

The Basics

Deep fry thermometers, also used for candy-making, are designed to provide precise temperature measurements, withstand high heat, and enable you to work hands-free in order to avoid burning yourself.

  • When deep frying, monitoring temperature of the oil is crucial:

    • Too hot and your food will dry out and/or burn.

    • Too cool and your food won’t cook properly, and the oil will seep in, making it greasy and unappetizing.

    • Just right and the oil heats the food’s internal water to the steaming point, cooking the food from the inside out. This internal steam also prevents the oil from being absorbed into the food.

There are a variety of thermometer designs to consider:

  • Bulb thermometers work on the same principle as traditional mercury thermometers used for taking body temperature or measuring atmospheric temperature. A non-toxic liquid within the tube expands with the heat of the oil or candy. There are two main types of bulb thermometers:

    • Glass tube bulb thermometers are designed as a tube within a tube. They usually have a clip enabling them to be mounted on a pan.

    • Ruler bulb thermometers house the narrow glass tube within a metal frame, which is then clipped to the side of the pan. The frame ensures the bulb is at the correct distance from the bottom of the pan.

  • Dial, or mechanical, thermometers use a bi-metallic strip to measure heat. Two different metals with different rates of expansion/contraction are bonded together, often in a coil. The difference in expansion causes the strip or coil to bend, which controls a needle that points at temperatures on a dial face. There are two types of dial thermometers:

    • Instant-read dial thermometers are used to take the temperature of many things, from steamed milk to roast beef. They are not oven-safe, so they need to be quick to take temperature while the oven door is open.

    • Oven-safe thermometers are typically used for measuring meat temperature. A probe is inserted into a thick area and remains there while the meat roasts. Oven-safe dial thermometers without probes are also available and are good for using with the barbecue or checking your oven calibration.

  • Digital (or electronic) thermometers are battery-operated and measure temperature with a microcomputer, displaying a reading on an LCD screen. There are a couple of varieties:

    • Instant-read digital thermometers are not oven-safe and work the same way as the instant-read dial thermometers.

    • Remote digital thermometers have an oven-save probe attached to a thin, oven-safe cord that plugs into a digital monitor. The cord is thin enough that it won’t hinder the closing of the oven door. These monitors have several functions, including displaying current temperature, alerting you to when it reaches the desired temperature, And acting as a timer (counting up or down).

Features to look for in a deep fry thermometer:

  • Accuracy: in non-digital models, look for small gradations of measurement (e.g. every 2 degrees rather than every 5-10 degrees). In digital models, look for one that measures by single degrees.

  • Easy-to-read: make sure the numbers and markings big and clear enough to read easily. If your bulb or dial model has markings for candy-making (e.g. soft ball, hard ball) or deep frying (e.g. chicken, French fries), make sure they words are clear and don’t obscure the numbers or measurement lines.

  • Speed: how fast a thermometer registers changes in temperature can range from 2-30 seconds or more. Bulb and dial thermometers tend to be slower than digital models. A delay of 30 seconds can be detrimental to the success of your recipes, but unfortunately most models don’t advertise the temperature change speed.

  • Pan clip: since they must be constantly immersed in hot liquid, a pan clip is critical. Look for one that is adjustable so that it can move up and down the length of the thermometer.

  • Tip sensors: since the temperature sensors of most dial thermometers aren’t located at the tip (as in bulb or digital models), it must be immersed in a minimum depth of liquid. Bulb and digital thermometers usually have the sensor right in the tip.

  • Dual units: look for a thermometer with both Fahrenheit and Celsius clearly marked. Most digital thermometers will have a switch to change the display back and forth.

  • Settings and alarms: with digital thermometers, look for as many presets, timers, and alarm features as possible to help ensure you don’t over- or undercook.

  • Auto-shut off in digital thermometers is helpful for saving batteries.

  • Manual calibration features allow you to reset a thermometer that might have gone off.

Be Aware

  • Always heed the recommended temperature range of your thermometer to avoid damaging it.

  • Never allow the tip of your thermometer to touch the bottom of the pan while deep-frying or making candy, or it could read incorrectly and may become permanently damaged by the high heat.

  • Always allow your thermometer to cool before washing it. Sharp changes in temperature can cause a thermometer’s tube to shatter or its sensor to become damaged.


Where better than a fry shop to test out our digital thermometers? Pass the ketchup!

  • TruTemp by Taylor Candy (bulb: glass tube): $4
. . Amazon.ca Amazon.com
  • Maverick Redi-Chek Candy/Oil Deep Fry Thermometer (bulb: ruler): $15
. . Amazon.com
  • Taylor Connoisseur Series Candy/Deep Fry Thermometer (dial: instant-read): $32
. . Amazon.ca Amazon.com
  • CDN Combo Probe: thermometer, timer & clock (digital: remote): $44
. . Amazon.ca Amazon.com

(Note: prices listed above are approximate and in Canadian dollars)

Deep Fry Test

We tested each thermometer for speed, accuracy, and ease of use in a vat of boiling oil, while we deep fried ourselves some delicious Mars bars:

  • The TruTemp tube thermometer was a little difficult to read, especially when the glass steamed up. It was also off by 11 degrees in our accuracy test!

  • The Maverick Redi-Chek ruler thermometer was easy to use, but it can’t be used for other things like meats. Big strike against it. And when we washed it after the test, the numbers rubbed off. Not good!

  • The Taylor dial thermometer was very easy to read, with a large face, but it was a bit tippy and hard to secure. Also, it only had Fahrenheit measurements.

  • The CDN combo probe digital thermometer was easy to read and easy to use. Plus, it was also versatile and can be used for deep frying, candy-making, meat, and other things.


Even though the CDN combo probe digital thermometer was the most expensive, it’s also the most versatile, and has some features that can’t be beat by any of the others we tested. So while you might save some money on a non-digital model, you may end up having to buy more than one thermometer for different things. The versatility and ease of use of the CDN digital thermometer makes it our top pick.

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