Thames & Kosmos Candy Chemistry handleiding

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The Chemistry of Sugar Crystals

When solutes fall out of solution, scientists

say they precipitate out of the solution. This

can happen when the amounts of solvent or

solute change, or when the conditions such

as pressure or temperature change. When the

solute precipitates out of solution,

sometimes it will do so molecule by molecule,

in a slow, orderly way. Because the molecules

are all the same, they tend to ﬁt together, or

stack, in the same way, forming solid crystals

with organized shapes. This process is called

crystallization. Crystals can also form when

molten items solidify or freeze.

CRYSTALLIZATION

Common table sugar, or sucrose, is a

molecule called a carbohydrate because it

contains carbon, hydrogen, and oxygen

atoms. The simplest carbohydrates are called

monosaccharides, such as fructose and

glucose, which are the building blocks of all

other sugars and carbohydrates. Sucrose is

actually made of a fructose molecule

combined with a glucose molecule.

The molecular structure of sucrose causes it

to form monoclinic crystals when dry. This

basically means they form elongated and

skewed cubic crystals. When put into water,

sugar crystals will dissolve. The amount of

sugar that will dissolve in water depends on

the temperature of the water: the hotter the

water, the more sugar can ﬁt into it, to a

point. A very hot solution that has a lot of

sugar in it is called a supersaturated solution.

These solutions are used in candy making.

Unfortunately, it is hard to keep sugar in

supersaturated solutions when they start to

cool. The sugar wants to crystallize. These

crystals are desirable in some candy, such as

rock candy, and undesirable in other candies,

such as hard candy and caramels. So for

these candies, methods have been developed

to keep the crystals from forming. Methods

include adding simple sugars to the solution

which block the sucrose from crystallizing,

and adding acids to the solution which break

down the sucrose a little to keep it from

crystallizing.

← Ice crystals

Sucrose

molecule

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