Courtesy Delphine Ménard
Just because everyone knows it's true, doesn't make it so. For centuries, candy makers have wrung their hands over the vagaries of sugar. See, sugar doesn't always melt at the same temperature. Turns out, that's because it's not really melting. It's decomposing.
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"We saw different results depending on how quickly we heated the sucrose. That led us to believe that molecules were beginning to break down as part of a kinetic process," said Shelly J. Schmidt, a University of Illinois professor of food chemistry.
Schmidt said a true or thermodynamic melting material, which melts at a consistent, repeatable temperature, retains its chemical identity when transitioning from the solid to the liquid state. She and Lee used high-performance liquid chromatography to see if sucrose was sucrose both before and after "melting." It wasn't.
"As soon as we detected melting, decomposition components of sucrose started showing up," she said.
To distinguish "melting" caused by decomposition from thermodynamic melting, the researchers have coined a new name—"apparent melting." Schmidt and her colleagues have shown that glucose and fructose are also apparent melting materials."
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