Water Activity

Water Activity Diagram

Water activity (Aw) is the dimensionless ratio between the vapor pressure of water in the sample (P) and the vapor pressure of pure water (P0) at the same temperature. The water activity level reflects the thermodynamic energy status of the water in the system, ranging from 0 to 1.00. This value can also be expressed as the equilibrium relative humidity (ERH) of the headspace above the sample in a closed system, ranging from 0% to 100%.

Water activity is a critical parameter for the safety, quality, and shelf life of various products, particularly in the food, pharmaceuticals, cannabis, and cosmetics industries. Monitoring and controlling the water activity of the product is important for several parameters and processes such as

  • Microbial growth and molding
  • Changes in the product texture, color, odor and/or taste
  • Moisture migration
  • Caking and clumping
  • Chemical reactivity and stability

The instrumentation utilized at PTL employs a state-of-art tunable diode laser that can measure the water activity of a sample in a temperature-controlled environment. Measurements can be made on even the most challenging samples containing volatile compounds, such as oils, sauces, tobacco, spices, and alcohols. 

Water activity is different from moisture content or the quantitative amount of water in a sample. The relationship between water activity and moisture content can be explored through a water sorption isotherm curve. In addition to water activity testing, PTL can also provide testing services for moisture content (loss on drying by oven drying or TGA methods) and water sorption isotherm determination by dynamic vapor sorption.

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Click the button to the right to learn how to submit sample material for particle size and characterization analyses. If you have more questions along the way, please contact us.