Minimal Aw values for growth of microorganisms, as well as influence of Aw on viability loss, vary with the food characteristics and the food environment. In a homogeneous food, Aw will remain unchanged provided other factors do not change. However, a heterogenous food with ingredients or items of different Aw (e.g., a sandwich or a meal with different items in the same package) will generate a gradient. This can lead to microbial growth in an item preserved by reduced Aw alone and stored with an item of high Aw containing a preservative. Also, condensation of water during storage with temperature fluctuation, followed by dripping of moisture in some areas of food, can alter a safe Aw level in these areas to an unsafe state