Finally, a Good Thermometer for Home Preserving

Reader Contribution by Linda Ziedrich
Published on January 18, 2016
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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.

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