spices tested by water activity
Granola for Water activity testing

Water Activity

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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  • May be used to justify reduced Microbiological Testing (Aw < 0.60)
  • Measures water molecules even in the presence of volatiles


  • Analysis temperature of 25°C (Standard), 15°C to 50°C (with additional calibration required)

Sample Requirements

Minimum of 5 mL, 7.5 to 15 mL recommended.

Detection Range

0.000 to 1.000 Aw.

Data Reported

A graphical plot of Water Activity over Time is provided, along with the Average Aw value from 4 consecutive readings within ±0.001Aw


Particle Technology Labs uses the AquaLab TDL by Meter Group.

AquaLab TDL