When home preservers have asked me what sort of thermometer they should use, I’ve never had good advice for them. I teach people to assess the readiness of their jams, jellies, and preserves by various tests: Does the liquid “sheet” off the spoon? Does the jam mound in a chilled dish or show wrinkles when you disturb its cooling surface? Does the syrup “spin a thread” in a glass of cold water?
Yet I often specify temperature goals for verifying these visual tests. Knowing the temperature really helps, for example, in the case of fruits whose juices gel slowly and so fail to “sheet” when they have reached gelling temperature. But how can you know that your boiling liquid has reached gelling temperature when your thermometer simply does not work?
Thermometers fail us in many ways. The glass capillary tube of an old-fashioned candy thermometer slips up or down in relation to the scale. The paint wears off the scale. Thermometers that must be left in the pot get in the way of the spoon and fall in the jam. Dial thermometers must be calibrated when you buy them and frequently thereafter. For an “instant-read” thermometer, the “instant” may last ten seconds or more—long enough to burn your fingers.
Digital thermometers often flip out a few degrees beyond boiling. My husband bought an expensive, long-probed thermometer that measured some 30 degrees off and could not be calibrated. He bought another that showed wildly fluctuating temperatures over about 215 degrees Fahrenheit. Even my little digital CDN, the most reliable thermometer I ever had until now, goes blank when the temperature nears 220 degrees; when I remove the thermometer from the heat, the display reappears in Celsius instead of Fahrenheit. And thermometers of all kinds fog up and become unreadable.
So I am extremely happy with my Christmas present: a little digital thermometer called the Javelin Pro. It’s made in the style of the expensive Thermapen: With the probe folded against the handle, these thermometers are small enough to fit in a breast pocket, but when the probe is fully extended the thermometer is long enough — 10.5 inches, in the case of the Javelin Pro — to keep your hand well away from the heat. I like to extend the probe just 90 to 120 degrees, so my hand is outside the rim of the pot while I take the temperature of my jam.
Many manufacturers are now making Thermapen-type thermometers, which start at about twenty dollars. All have large, easy-to-read screens, and some of the screens, including mine, have backlighting, which enhances readability even when you’re not working in the dark. And these thermometers tend to be fast and accurate. My Javelin Pro responds in only 3 to 4 seconds, and it’s accurate to 0.9 degrees F.
You can’t calibrate these thermometers, but you shouldn’t need to; the Javelin Pro is supposed to retain its accuracy through the three-year warranty period. High temperatures don’t upset my thermometer; I’ve used it successfully for jams and jellies already, and the manufacturer claims that it is accurate all the way to 482 degrees F. The big display does not fog up.
I see only two general disadvantages to Thermapen-type thermometers. First, you can’t switch the readout between Fahrenheit and Celsius. Instead you must buy either a Fahrenheit or a Celsius thermometer, although you may be able to change the setting by fiddling with the thermometer’s insides.
Second, you must replace the battery when it wears out — but fortunately that battery is likely to be long-lived. My Javelin Pro takes a CR2032 battery that is expected to last 3,500 hours.
The Javelin Pro has a couple of special features that made me choose it over similar models for my Christmas list. A hidden magnet lets it magically stick to the refrigerator. If you have a non-magnetic refrigerator, no problem: The Javelin Pro also has a hole at the handle end through which you can loop a cord, to hang on a hook or around your neck. No more fishing through a drawer every time you need a thermometer.
If you’re feeling wealthy, however, you might want to bypass the Javelin Pro for a genuine Thermapen. All the competition from imitators has pushed its maker, Thermoworks, to continually improve its thermometer. The latest model, the Super-Fast Thermapen, responds in only 2 to 3 seconds and is accurate to 0.7 degrees F. You can set the thermometer to show you tenths of a degree, if you prefer, instead of whole degrees, and the display will turn among four directions depending on how you hold the instrument. The battery is an AAA, so it’s easy to find a replacement. Best of all, this newest Thermapen is not just water-resistant; it is waterproof.
Linda Ziedrich’s books, Joy of Pickling, Joy of Jams, Jellies, and Other Sweet Preserves, and Cold Soups, spring from both her experiments with produce from her vegetable garden and orchard and from her studies of culinary traditions around the world. Linda develops products for Crisp & Co., a pickle manufacturing company based in Delaware, and teaches preserving classes. She devotes much of her volunteer efforts to promoting good eating as a founder and coordinator of the Santiam Food Alliance, as an Oregon State University Master Food Preserver, as a board member of Slow Food Corvallis, and as a member of the Oregon Ark of Taste committee for Slow Food USA. She blogs at A Gardener’s Table. Read all of her MOTHER EARTH NEWS posts here.
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