As the water activity of foods and ingredients is lowered, fewer organisms are able to grow in the product. The only pathogen capable of growing below 0.90 is S. aureus. Research indicates this organism may produce enterotoxin at water activities as low as 0.867. Intermediate-moisture foods also are regulated to Aw levels of 0.85 or below to assure microbiological safety.
Reducing water activity, along with the use of mild heat, organic acids or other antimicrobials, creates a hostile environment for microorganisms. When producing dry ingredients, blended products or other foods, understanding the water activity of each of the components of a food system helps ensure the products look, perform or taste as expected.