except in some salt or sugar solutions. Higher water activity substances tend to support more microorganisms than foods with a lower wa- ter activity. Consider that most bacteria usu- ally require a water activity of ≥0.91 to grow, whereas fungi can thrive at water activity of 0.70. Consider, too, that water tends to migrate from substances with high water activity to substances with low water activity. We often confuse water activity with mois- ture content and water content. Here is the dierentiation between these terms. Water in products or ingredients indicates the liq- uid water content, which is a quantitative or volumetric analysis that determines the total amount of water present. Whereas, the mois- ture content of a food is essential in meet- ing product nutritional labeling regulations, specifying recipes, and monitoring food man- ufacturing processes. If using only the water content values, it is impossible to know how available the water is in the product to sup- port microbial growth or influence product quality. Therefore, available water is another name for water activity. The water content varies from product to product and from formulation to formulation.
As an example, one safe, stable product might contain 15% water while another contain- ing just 8% water is susceptible to microbial growth. Although the wetter product contains proportionally more water, its water is chemi- cally bound by other components, making it unavailable to microbes. Looking at it a bit dif- ferently, water activity is sometimes described in terms of the amounts of bound and free water in a product. These terms, however, fail to define all aspects of the concept of water ac- tivity. Taking it one step further, the issue is not whether water is bound but how tightly it is bound and the energy required to remove water from the system. In the mid-1990s, the first truly portable water activity measuring device significantly broadened the range of foods we could assess in the field for potential risk of foodborne illness. It rapidly became a valuable must- have tool, particularly for those environ- mental health professionals who worked in institutional environments, and particularly with correctional kitchens. The burgeoning incarcerated population puts a strain on all food service equipment, particularly refrig- eration. By measuring the water activity of
the various foods kept “on ice,” we could as- sess which foods were deemed to be on the cusp of potentially hazardous and treat those foods as worst-case scenarios. Field measure- ment eliminated collecting samples, trans- porting samples to the laboratory, and wait- ing for sample results. In real time, we could now maximize valuable refrigeration space for those foods most sensitive to tempera- ture controls. The science and accompanying technology proved invaluable. Yet, with all this information, we still are called on to arbitrate a battle of wits stem- ming from a violation cited for not placing the croutons, raisins, sunflower seeds, or arti- ficial bacon bits on ice in a salad bar, or com- pelling a short-order cook to keep butter and bacon at safe temperatures, or maintaining that the peanut butter, mayonnaise, jams, and table condiments are refrigerated at all times. So that we can avoid these minor but signifi- cant clashes of ideas and traditional ways of doing things, understanding water activity and measuring it in the field goes a long and professional way.
Contact: powitz@sanitarian.com.
Davis Calvin Wagner Award
Do you know an exceptional diplomate of the American Academy of Sanitarians (AAS) who is a leader who shows professional commitment, outstanding resourcefulness, dedication, and accomplishments in advancing the environmental health profession? Nominate them to be recognized with the AAS Davis Calvin Wagner Sanitarian Award. Nomination deadline: April 15, 2024 www.sanitarians.org/Awards
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January/February 2024 • Journal of Environmental Health
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