Microbial Growth
Microorganisms have a limiting water activity level below which they will not grow. Water activity, not moisture content, determines the lower limit of "available" water for microbial growth. Since bacteria, yeast, and molds require a certain amount of "available" water to support growth, designing a product below a critical aw level provides an effective means to control growth. Water may be present, even at high content levels, in a product, but if its energy level is sufficiently low the microorganisms cannot remove the water to support their growth. This ‘desert-like' condition creates an osmotic imbalance between the microorganisms and the local environment. Consequently, the microbes cannot grow and its numbers will decline until it eventually dies.