How does drying food slow the growth of microorganisms?

Drying, or dehydration, preserves food by extracting moisture, which is essential for inhibiting the growth of microorganisms. Foods with high water concentrations are more susceptible to deterioration caused by microbial contamination and enzymatic activity.12

By removing water, the concentration of solutes in the food increases while the available water decreases. This reduction in available water—often referred to as water activity—is critical because microorganisms require moisture to thrive and reproduce. For instance, yeasts generally cannot grow at a water activity level below 0.9, and molds are typically unable to grow below 0.8. In many products, such as bakery items, keeping the moisture content below 12 to 14 percent is sufficient to completely inhibit the growth of bacteria, yeast, and molds.234

Ultimately, by lowering the water content, dehydration creates an environment that is unfavorable for the survival and proliferation of spoilage-causing organisms.51