Water Activity Measurement


The measurement of water activity or equilibrium relative humidity is a key parameter in the quality control of moisture-sensitive products or materials. Water activity is by definition the free or non chemically bound water in foods and other products. The bound water cannot be measured with this method.

ROTRONIC offers fast and accurate instruments for the measurement of water activity of foods, seeds, pharmaceuticals, cosmetics, etc. ROTRONIC unique technology guarantees water activity measurement at the lowest possible purchase price.

Water Activity (aw) or Equilibrium Relative Humidity (ERH) measurement is a widely used the food and pharmaceutical industries as part of quality control and production procedures to control the effect of moisture on issues such as shelf life, taste, texture, contaminant growth (e.g. mould), agglomeration and drug stability.

In the quality assurance, goods receipt or production environment, the reliabilty and long term stability of Rotronic measurement systems ensures accurate and repeatable results. Our certified standards enable the user to directly check instrument calibration in a matter of minutes with traceability to national standards.

Aw-Quick is an accelerated measurement mode that provides the user with results in a few minutes, and is available in both our benchtop and portable instruments.



Stable temperature yields precise measurements.

Temperature-stabilized measurement

With AwTherm, ROTRONIC offers a professional, high-end laboratory unit for temperature-stabilized measurement of water activity in the foodstuffs, cosmetics, or pharmaceutical industries.
The wide control range permits measurements to be integrated directly in the tempered manufacturing or storage process. Water-activity measurement reacts very sensitively to variances in temperature. Stabilizing the temperature prevents imprecise results due to external temperature influences.

Exchangeable measuring head
A further advantage of AwTherm is that the measuring head is removable, which means that the probe can be temperature-calibrated or adjusted to give high precision.

The AwTherm shows its paces in island-operation mode, with its simple handling and clarity. No laboratory should be without the device in conjunction with the ROTRONIC HW4 software

Why measure water activity?
The free water in a product influences its microbiological, chemical and enzymatic stability. If there is too much free water present, the products spoil; too little water can be detrimental to the product characteristics.

Water activity Contaminants
aw = 0.91..0.95 Many bacteria
aw = 0.88 Many yeasts
aw = 0.80 Many mildews
aw = 0.75 Halophile bacteria
aw = 0.70 Osmiophile yeasts
aw = 0.65 Xerophile mildew

Measuring water activity provides useful information about characteristics such as cohesion, storage lifetime, clotting or pourability of powders, tablets, etc., or the adhesive properties of coatings.


  • Highest precision through exact stabilization of temperature
  • Wide temperature-control range
  • Excellent reproducibility
  • Excellent long-term stability
  • Variable size of sample container
  • Reference probe exchangeable for calibration or cleaning
  • Quickest measurements with the AwQuick function
  • Simple operation via Touch Interface
  • Conforms to ISO 21807 / EMC 2008/108/EC / IEC EN 61010-1:2010

ROTRONIC provides a high-end laboratory device, the HygroLab C1, for water activity measurements from as many as four separate probes. Use multiple stationary probes and insertion probes for measuring water activity in cheese, meat, tobacco, building materials, animal feed, pharmaceuticals products and much more.


ROTRONIC provides a high-end laboratory device – the HygroLab C1 – for water activity measurements with up to four probes. Connect station probes and insertion probes for measuring water activity in cheese, meat, tobacco, building materials, animal feed, pharmaceuticals products and much more.

Validated software
Easy-to-use and intuitive, the laboratory grade indicator can be used by anyone. HW4 running on a PC provides remote monitoring with charting and data recording functions.

• 4 input channels for HC2 station probes or HC2 insertion probes can be connected for measurement of water activity, relative humidity and temperature
• Aw Quick function for fast measurement results (typically 4-5 minutes)
• Audible alarm to indicate completed measurement
• Saves up to 2,000 data records with %RH, °C/°F, date and time