Sucrose Doesn’t Melt – But Why?

Sucrose, better known as sugar (and yes, that’s the sugar which we all put in our coffee and on our strawberries), has long had a problematic melting point for scientists. Unlike H²O, there is no fixed temperature at which ice can be melted into water – and frozen vice versa.

However, up until recently, scientists believed that the trouble lay in improper methods of detection, faulty equipment or impurities in the samples. Now, they have discovered that they have been unable to find sugar’s melting point for the simple reason that it does not melt.

Decomposing, not Melting

When an ice cube reaches a specific temperature (0°C), it will begin to melt. Similarly, at the same temperature, water will begin to freeze into ice. However, sugar does not behave in this manner at all. Rather than melting at a specific point, its compositional change depends entirely on the heat of the flame that is being used to alter it. Even more interestingly, it can’t be “unmelted;” once the sugar has been heated to a point where it appears to melt, it can never return to just being sugar.

This is because in actual fact, it is not melting at all, but rather decomposing. This was confirmed by a professor of food chemistry at the University of Illinois, Shelly J. Schmidt. “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,” she explained.

In order to confirm their suspicions, she and her team used the technique of high performance liquid chromatography (HPLC) to analyse the sample before and after being heated. They found that as soon as the sugar began to melt, it contained decompositional qualities – namely, fructose and glucose.

These are components of sucrose, but only reveal themselves when a chemical reaction takes place. In this case, the reaction resembled the melting of the sugar… but it wasn’t actually melting. It was decomposing, and as a result, the fructose and glucose can never be fused back together into sucrose.

Practical Uses for the Knowledge

Recently, a team of researchers (also from the University of Illinois) have developed a new device for detecting the presence of common viruses and bacteria in the bodily samples of patients. The breakthrough in the home DNA-testing kit came when the scientists were able to convert the enzyme invertase from a sucrose into a glucose, which is able to be detected by the device. The latest revelation about sucrose’s decomposition can only aid such studies.

Meanwhile, in more mundane pursuits, the knowledge can simply help food scientists to better understand the behaviour of sugar when heated. This will allow them to achieve maximum caramel sweetness and avoid the unpleasant burnt flavour that sometimes accompanies it.