In products such as biscuits and boiled sweets, which contain small amounts ofwater and large amounts of sugar, the relative moisture level is lower than the ambient humidity. Without protective packaging, these products will absorbmoisture from the air.
Sugar’s ability to bind water in foods is based on the ratio between crystallised and dissolved. Any change in this ratio during production or storage affects the amount of water that the food can bind. Because sugar binds water, reactions that need water are delayed if sugar is present. The shelf life of bread is extended because sugar causes water to be retained for longer in the bread.
Bread and cakes baked with syrup will be more moist and have a longer shelf life than products made with sugar. This is due to the fructose content of the syrup, because fructose binds more water than sugar.