Candy Crystallization

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Heating phase

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End pointcooking temperature

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

Cooling phaseU

n sat

ura t

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End pointcooking temperature Unsaturated solution

Saturation point(solution has allthe sugar it candissolve)

SupersaturatedSolution (solutionhas more sugar than it should beable to hold)

Room temperature

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 (has all the sugar it can dissolve at that temperature)

Supersaturation

• As the temperature drops below the saturation point, the solution becomes supersaturated (has more sugar than it should be able to dissolve)

• We can only make candy (i.e., recrystallize the sugar) when we are in the supersaturated region

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

Sugar crystal growth

Sugar

Sugar crystal growth

Sugar

Sugar crystal growth

Sugar

Sugar crystal growth

Sugar

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

Inducing crystallization

Largecrystals,coarse

Inducehere

Induce here

Small crystals,smooth

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