Water activity (aw) is one of the most critical factors in determining quality and safety of the goods you consume every day. Water activity affects the shelf life, safety, texture, flavor, and smell of foods.
Most bacteria, for example, do not grow at water activities below 0.91, and most molds cease to grow at water activities below 0.80. By measuring water activity, it is possible to predict which microorganisms will and will not be potential sources of spoilage. Water activity--not water content--determines the lower limit of available water for microbial growth. In addition to influencing microbial spoilage, water activity can play a significant role in determining the activity of enzymes and vitamins in foods and can have a major impact their color, taste, and aroma. It can also significantly impact the potency and consistency of pharmaceuticals.
It is also important to the stability of pharmaceuticals and cosmetics. While temperature, pH and several other factors can influence if and how fast organisms will grow in a product, water activity may be the most important factor in controlling spoilage.
The question as to whether the chilled mirror dewpoint method of determining water activity, or the capacitance based method is better for an application, has primarily to do with accuracy and convenience. The chilled mirror dewpoint method is a primary method, and has an accuracy of +/- .003 aW, compared to +/-.008 aW for the Rotronic capacitance based sensors.
Capacitance based water activity meters use an indirect method of determining water activity, and are slightly less accurate, although well within the accuracy parameters for quality control usage, but provide more features and convenience
Probe type sensors are available, as well as hand held instruments and sophisticated software, with report generation capabilities.
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