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aw of Component Mix
Isotherm BET/GAB
Recipe Water Activity
Download WA

Water Analyser Series

The WATER ANALYSER SERIES is a suite of programs designed to run under Microsoft Excel on an IBM compatible PC running Microsoft Windows, and includes comprehensive on-line hypertext-style help. The programs were written by Ron Webb for use in the food industry, and in various courses taught by Dr. Theodore P. Labuza, University of Minnesota.

The programs cover all aspects of water activity isotherm determination, plotting and estimation, packaging film permeation, kinetics and shelf-life estimation.


 Water Activity Mix
  Isotherm BET/GAB
  Recipe Water Activity
  Permeance of Packaging Materials
  Packaged Food Shelf Life

Module Descriptions

Water Activity of a Component Mix

Will these sultanas go hard and the corn flakes go soft?

  • This program estimates the water activity and moistures of a mix of components after they have reached equilibrium.
  • Isotherm of the mix is estimated.
  • If diffusion data is available, the time taken to reach equilibrium is estimated.

    Water Activity of a Component Mix program details

Isotherm BET/GAB

What is a safe moisture for this product to prevent mould?
How much water can I safely put in this product?

  • This program is designed to produce isotherms and calculate the associated BET and GAB parameters based on experimental data sets of moisture and water activity of foods or other substances.
  • Isotherms on a wet and dry moisture basis are plotted.
  • Throughout the program, moisture data may be entered on a dry or wet basis, and in raw data entry pan weights may be used.
  • Water activity may be entered directly, as the salt used to obtain equilibrium, or as a refractive index if using the CSIRO method.
  • Isotherms are plotted based on the GAB equation, and optionally the BET equation and the linear isotherm of best fit.
  • Data sets and calculated parameters may be stored in a database for later retrieval and modification.
  • A second isotherm may be overlaid on the first for comparison.
  • The program will estimate the water activity based on a known moisture, or the moisture based on a known water activity.
  • The mould-free shelf life of cake-type products may be estimated.

     Isotherm program details


What will the aw of this product be if I send it to Japan in summer?

  • This program is designed to calculate and plot the isotherm of a food at any temperature, given the isotherm data at 2-4 other temperatures.
  • The database from the Isotherm BET/GAB program to containing previously stored isotherms is used.

        Clausius-Clapeyron program details

Recipe Water Activity

What is the expected aw of this product formulation, and how can I change it

  • This program is used to predict the water activity and isotherm for a food formulation, using the Ross equation, based on either the initial moisture or final moisture after processing.
  • Isotherms on a wet and dry moisture basis are plotted.
  • It contains an ingredients database, which may be added to.
  • A second database is used to store and retrieve recipes.
  • The final moisture required to achieve a target aw may also be estimated.
  • The mould-free shelf life for cake-type products at a range of temperatures is also predicted.

        Recipe Water Activity program details

  • An enhanced version designed to optimise the recipe for minimum cost or aw within user- defined constraints is available as an optional extra.

Permeance of Packaging Materials

Is this packaging film good enough?

  • This program is designed to calculate the permeance (k/x), permeability (k) and water vapour transmission rate (WVTR) of a packaging film, based on experimental data.
  • Includes a maintainable film database, which may be used in the GAB Shelf Life program.

Packaged Food Shelf Life

How do I look at the total picture: product, packaging and the environment?

  • This program calculates the change in moisture and water activity over time for a packaged food, based on an entered set of time periods with average humidity and temperatures.
  • The program may be used to determine the film permeance required to achieve a desired moisture/water activity profile.
  • Uses the linear isotherm for calculations.
An enhanced version which uses the more accurate GAB isotherm for calculations, and also calculates and graphically displays the loss of "freshness" in terms of mould-free shelf life for cake-type products, is available as an optional extra. This program may also be used to estimate the shelf life based on reaction kinetics, such as the degradation of aspartame.

Reaction Kinetics

How do I calculate the breakdown of vitamins in my product?

  • This program is designed to assist with any kinetic study.
  • It will determine reaction order and rate constant, and uses the Arrhenius equation to predict the rate at any temperature. All are plotted.
  • Q10 values are calculated for a range of temperatures.


How fast will this product take up water?

  • This program calculates the sorption diffusion rate for foods using the Crank, Langmuir or Crank Internal Control equations.


How fast will this product dry in the oven?

  • This program calculates the diffusion coefficient and critical moisture for foods undergoing moisture loss during drying, using the Sherwood equation.


Where do I get the data for this solution to put into the ingredients database for the Recipe aw program?

  • This program calculates the Norrish constant for solutes, based on experimental data sets of concentration vs water activity. An enhanced version of the Norrish equation may be used, which uses an activity coefficient to achieve greater accuracy.

        Norrish program details

Formulation Water Activity Comparison

  • This program is not a 'working' model.
  • Demonstrates and compares various methods to estimate the water activity of a formulation.


These programs require an IBM compatible computer with Microsoft Windows Windows 98, and Microsoft Excel Version 97 or later.

The Water Analyser Series may be downloaded for evaluation purposes. This is a fully featured version, but may only be used for a limited period. If you decide to purchase, a password will be supplied to enable continued use, and an installation diskette with manual will be supplied.

The setup program requires the VB files VBRUN300.DLL and THREED.VBX, which must be either in the Windows\System directory or the same directory as the setup files.

Download Water Analyser Series

The file aw.exe should be downloaded to a temporary directory. Double-clicking it will extract the setup files. If you don't already have the VB files, download the file vbfiles.exe to the temporary directory and extract the VB files. Run the setup program setup.exe to install the Water Analyser Series in the directory of your choice. All of the files in the temporary directory may then be deleted.

These files are self-extracting zip files. If either file fails to extract, check the file size. If the file is not the size indicated above, the download failed and you should download it again.

If you are unable to successfully download the Water Analyser Series, it will be emailed as an attachment on request, or sent to you by mail.



US$450 for a single-user licence.  It may be installed on a network drive and used my multiple users, but only one at a time.

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Last modified: 10-Aug-2008