whereas glucose is slightly less soluble and therefore produces a less thick solution when dissolved in
water. Sucrose is also surprisingly soluble in water – it is actually the second most soluble sugar in
water and can dissolve in half its volume of water to produce a thick solution.
After a certain point, no more sugar can dissolve in a sugar solution because there will be no more
water molecules available to bond with the added sugar –the sugar will stay in crystal form and will not
dissolve. We say that the sugar solution is saturated.
Effect of heat
Unlike the carbohydrates, proteins and fats, the sugars are small and stable molecules that are
remarkably resistant to heat. A mixture of a sugar and water can be heated to boiling temperatures
without affecting the sugar structure. As the mixture is boiled, water molecules evaporate from the
mixture, and gradually the solution will become more and more concentrated in sugar, the sugar
molecules will start to bond with themselves to form pure masses or solid crystals. This is how sweets
The boiling temperature of a sugar solution will always be higher than 100°C. This is because heat is
needed to not only break the water-water linkages but also to break the strong sugar-water linkages.
So the solution will need to be heated to a slightly higher temperature before the water can become a
Also, the more concentrated the solution is in sugar, the higher the boiling point. Therefore, as the
solution is heated, more and more water evaporates, so the solution become more and more
concentrated in sugar, further increasing in boiling point. A sugar solution with a sugar concentration of
90% will boil at about 125°C.
Extreme heat –caramelisation
If simple sugars are heated to a sufficiently high temperature (which will happen when al the water has
evaporated from a sugar solution), it will eventually start to develop a characteristic “caramel” taste as
the sugar molecules themselves start to break down. The monosaccharides are fairly reactive, and