The reason why bacteria doesnot grow in high concentration of sugar is because of sugar’s high osmotic and dehydrating ef fects. Sugar, whether in solid or aqueous form, attempts to reach equilibrium with the sugar content of the food product with which it is in contact. This has the effect of drawing available water from within the food to the outside and inserting sugar molecules into the food interior. The result is a reduction of the so-called product water activity (aw), a measure of unbound, free water molecules in the food that is necessary for microbial survival and growth.Sugar’s other antimicrobial mechanisms include interference with a microbe’s enzyme activity and weakening the molecular structure of its DNA (Scientific American Journal).