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The Water Sorption Isotherm represents the equilibrium relationship between the water content of a food and its water activity (aw). At equilibrium, water activity is, in effect, equivalent to the relative humidity of the atmosphere surrounding the food.

Accurate definition of the water sorption isotherm is of considerable importance to processors of food and agricultural products.

Particular applications include drying of foods to ensure the required stability, mixing of foods and prediction of the sorption isotherm of the products and, packaging where the freshness of a product such as cheese depends upon the ability of the container to maintain the specified degree of humidity.
The water activity subgroup of COST 90 (physical properties of foods) has developed a method for determining sorption isotherms and showed that micro crystalline cellulose (MCC) could serve as a stable and homogeneous reference material. The reference material based on MCC is designed to ensure correct application of the method.


The original COST 90 method has been further refined in order to improve definition of the MCC oven drying conditions. The water content of the reference material (RM 302) has been certified at 10 water activities and allows the application of the COST 90 method to be checked over the normal range of interest.
The project is terminated: EUR report 12 429 (1989).


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BBSRC Institute of Food Research
EU contribution
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BS Bristol
United Kingdom

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Participants (10)