Industry Sectors Water Activity (Aw) is a measure of the water available for bacterial growth. Water activity is not necessarily linked to water content. Two products with similar water content can have very different Aw and therefore may have different spoilage rates. Like pH, as the Aw decreases, fewer groups of organisms are able to grow. A water activity of less than 0.85 is generally assumed to be shelf safe. Shelf safe means that pathogens (organisms that can cause illness) should not be able to grow. An Aw of below 0.60 means that practically no organisms will be able to grow. The following table indicates the Aw range at which selected bacteria can grow.
| Aw range | Inhibited by lower Aw's | Foods in range |
| 1.00-0.95 | Bacillus, Clostridium perfringens, Escherichia, Klebsiella, Pseudomonas, Proteus, Shigella, some yeasts | Fresh vegetable, fruit, meat, fish, milk bread and foods containing up to about 40% sugar or 7% salt |
| 0.95-0.91 | Clostridium botulinum, Salmonella, Seratia, Lactobacillus, Pediococcus, Vibrio parahaemolyticus, some molds and yeasts (Rhodotorula, Pichia). | cheddar and Swiss cheese, cured meats, foods containing 55% sugar or 12% salt |
| 0.91-0.87 | many yeast (Candida, Torulopsis, Hansenula), Micrococcus | fermented sausage (salami), dry cheeses, margarine, sponge cakes, foods containing 65% sugar (saturated) or 15% salt. |
| 0.87-0.80 | Staphylococcus aureus, most molds, mycotoxigenic penicillia, most Saccharomyces bailii species, Debaromyces | fruit syrups, uncooked rice, flour, fruit cake, country ham, fondant, high-ratio cakes. |
| 0.80-0.75 | most halophilic bacteria, mycotoxigenic aspergilli | jam, marmalade, glace fruits, marzipan |
| 0.75-0.65 | xerophilic molds (Aspergillus chevlieri, A. candidus, Wallemia sebi), Saccharomyces bisporus | rolled oats, fudge, jelly, molasses, some dried fruits, nuts. |
| 0.65-0.60 | osmophilic yeasts (Saccharomyces rouxil), few molds (Aspergillus echinulatus, Monascus bisporus) | honey, caramels, dried fruits, fruits containing 15-20% moisture. |
| 0.60-0.20 | no microbial proliferation | pasta, spices, whole egg powder, cookies, crackers, whole milk powder, dried vegetables. |
