On Sucrose
Although there are a whole bunch of sugars commonly used in food, sucrose is by far the most common. It’s cheap. It’s delicious.
Just look at it!
The chemical structure tells us a few things about table sugar. All the OH and HO groups (called hydroxyl groups) contribute to making the molecule extremely soluble in water: at room temperature, you can saturate 100g of water with 200g of sucrose. And as most cooks have experienced, it only becomes more soluble as you heat it. That’s why we might microwave simple syrup to help dissolve the sugar, even though we don’t really need to.
Sucrose is a disaccharide. The pentagon to the left is fructose, while the hexagon on the right is glucose. The oxygen molecule linking these two chains is called a glycosidic bond, which is prone to a reaction called hydrolysis. A water molecule will react with the bond to break the disaccharide into its two constituent monosaccharides. This is useful because glucose and fructose interfere in the formation of crystals, which could make a grainy or crumbly product.
Pure sucrose will never boil. When we’re boiling candy, it’s actually the water that’s boiling because it’s becoming steam. The sugar itself just hangs around there and becomes more concentrated in the syrup. Once you reach a certain point, though, the boiling will slow down because we have no water left, and the sugar will start to become caramel. It’s interesting how sugar, an ingredient that tastes nothing but sweet, can take on all sorts of bitter and aromatic notes as it caramelizes. Chemists are much less romantic about the whole thing and call it decomposition.
And for whoever might be curious: the different types of lines are used to represent the geometry of the molecule. But as far as candy is concerned, it doesn’t really matter. At the intersection of each line is a carbon atom, and there are hydrogen atoms that aren’t represented. Neither are particularly reactive.
This is the first in a series of entries dealing on the science of sugar. Next: a study of sugar’s solubility.