You might try a candy thermometer.
Water cannot exceed 212F / 100C at atmospheric pressure.
(Sea level... ~ 14.7 psi.)

Rigidity of your product will be due to sugar content.
Temperature will advise you of that via soft ball or hard
ball stage. I additionally use cold water-drop testing.
The stages come up a little suddenly, as noticed.
A thermometer will help you see the approach speed.
You want to exceed syrup, but fall shy of peanut brittle,
temperature wise. See also, "taffy."
BillSF9c

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