Reducing the available water in foods to prevent bacterial growth is one of the oldest forms of food preservation. Water activity ranges from 0 (absolutely dry) to 1.0 (pure water). Salmonella grows best at an aw of 0.99 but can survive for long periods of time in low aw foods, that is those foods with an aw below 0.85. Low aw foods do not support the growth of foodborne pathogens, including Salmonella spp. Nevertheless, foodborne outbreaks of salmonellosis have originated from these foods. These outbreaks occurred because even though low aw foods do not support the growth of Salmonella, apparently any contaminating bacterial cells are still able to survive on these foods.