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The Brunauer-Emmett-Tellet (BET) model can be used to describe how foods and other materials absorb and desorb moisture and how this affects Aw. It gives similar results in many instances to the Guggenheim–Anderson–de Boer (GAB) model and is equivalent to the GAB model when the GAB K constant =1.
I will add a tutorial later explaining the advantages of the model and how it can be used for product development and to produce moisture isotherms. The latter are required in certain jurisdictions for dried foods prior to the issue of export certificates.
To use the model you must obtain the BET constants for the product concerned. There is a significant volume of literature listing the constants for major products so you should be able to access these easily. Alternatively these can be derived using an Aw- meter. The constants are then added to the table below and the Aw values you have selected inputted. The calculator will then calculate the equilibrium moisture content for each value and plot it against Aw, to give a sorption or desorption isotherm.
Note the constants for a particular food or material will normally be valid for a restricted range of Aw and moisture values.
How to cite this article
Mullan, W.M.A. (2019) [On-line] Available from: Accessed: