Sorption isotherms of the tested brands of instant coffee were determined by the static dessicator method at 20°C. The equilibrium water content was significantly (α=0.05) dependent on the product type and water activity (a_w). A distinct increase in water content was observed in the coffees K2 and K3 at the value of a_w about 0.70 and in coffee K1 at the value of a_w about 0.50. Above specified value of a_w it is likely that capillary condensation occurred. The monomolecular layer capacity was determined from the BET equation (K1 – 6.3044; K2 – 5.0424; K3 – 6.7225 g/100 g of the dry substance); this, in turn, was used to calculate the specific surface of sorption (K1 – 221; K2 – 177; K3 - 236 m²/g). The value of a_w corresponding to water content at the monolayer level was also determined, thereby estimating the storage durability of particular coffee brands. The value of the energy constant, calculated from the BET equation (about 20 kJ/mol) indicated that the process of adsorption in the experiment was a physical phenomenon.