Permeability of different packaging materials and the water uptake were studied in stored yerba mate at different conditions of humidity and temperature. Water vapour transmission rate (WVTR) was evaluated using the quasi-isostatic method. During storage at high relative humidity conditions, WVTR values were of 500 gm2/day for paper and ranged from 16 to 22 gm2/day for laminated films. Values of package permeability and data of food isotherms were used to calculate the variation of internal water vapour activity and to predict the yerba mate water uptake. The predicted and experimental values were in good agreement. For similar high humidity storage conditions, yerba mate packaged with paper reached critical humidity content (9.5% d.b.) at the second day of storage whereas for the laminate films the humidity content stood below the critical value until a month of exposure.
