1. Candy Crystallization
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2. Heating phase
End point
cooking
temperature
Unsaturated solution

3. During the heating phase
The concentration of sugar in the solution is increasing due to the evaporation of water
The boiling point is increasing due to the colligative property of boiling point elevation, which says that as the concentration increases, the boiling point increases

4. Cooling phase End point cooking temperature Unsaturated solution
Saturation
point
Supersaturated
solution
Room temperature

5. During the cooling phase
There is no change in the sugar concentration
But there is a decrease in temperature
At some point (a unique combination of concentration and temperature) the solution will become saturated

6. Supersaturation
As the temperature drops below the saturation point, the solution becomes supersaturated
We can only make candy (i.e., recrystallize the sugar) when we are in the supersaturated region

7. Crystal formation But when should we induce crystal formation?
At a relatively high temperature, or
At a relatively low temperature?
The answer depends on understanding about sugar crystal growth

8. Sugar crystal growth
Sugar

9. Sugar crystal growth
Sugar

10. Sugar crystal growth
Sugar

11. Sugar crystal growth
Sugar

12. Sugar crystal growth
Sugar crystals grow by having sugar molecules deposited on their outer faces
If we cool the syrup down to just a little above room temperature, the crystals will have less time to grow before they reach room temperature and stop growing

13. Inducing crystallization
Induce
here
Induce
here
Large
crystals,
coarse
Small crystals,
smooth

14. Crystal size and texture
This is important because in candy (and frozen desserts) crystal size = texture
Large crystals = coarse, crunchy texture
No good
Small crystals = smooth, velvety texture
This is what you want