My battery-run candy thermometer was dead, and I decided to make caramel without using one. It apparently didn't get hot enough and is runny. How do I thicken it up now?
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Depending on what steps you took after cooling it, you may be able to reheat, bring to the proper temp, and do OK. Or, you could leave it as it is and just use it for a caramel syrup.
If you have to remake, test by dropping some in a glass of cold water. If it forms a ball when you push it together w/ your fingers, it is done.