Water activity (aw) has its most useful application in predicting the growth of bacteria, yeasts and molds. For a food to have a useful shelf life without relying on refrigerated storage, it is necessary to control either its acidity level (pH) or the level of water activity (aw) or a suitable combination of the two. This can effectively increase the product's stability and make it possible to predict its shelf life under known ambient storage conditions. Food can be made safe to store by lowering the water activity to a point that will not allow dangerous pathogens such as Clostridium botulinum and Staphylococcus aureus to grow in it. The diagram below illustrates the water activity (aw) levels which can support the growth of particular groups of bacteria, yeasts and molds. For example we can see that food with a water activity below 0.6 will not support the growth of osmophilic yeasts. We also know that Clostridium botulinum, the most dangerous food poisoning bacterium, is unable to grow at an aw of .93 and below.