The equilibrium vapour pressure above a food is determined not only by the temperature but also by the water content of the food, by the way in which the water is bound in the food, and by the presence of any constituents soluble in water. Under a given vapour pressure of water in the surrounding air, a food attains a moisture content in equilibrium with its surroundings when there is no exchange of water between the food and its surroundings.
This is called its equilibrium moisture content.