Aroma compounds are heat-sensitive and easy volatile components, which are lost with co-vapour during concentration by evaporation. Many authors found out that a loss of volatile aroma compounds was significantly smaller in fruit juice concentration by reverse osmosis than in concentration by evaporation. This work deals with the application of reverse osmosis for solution concentration of alcohols, esters and aldehydes, which are components of apple juice aroma. The influence of the membrane type, processing pressure parameters and shares of alcohols, esters and aldehydes in initial solution was investigated. Effect of the molecular mass and molecule structure on the permeate flux in model solution concentration by reverse osmosis was also observed. Influence of activity and activity coefficient of the mentioned compounds on the permeate flux was studied. Concentration by reverse osmosis was carried out by the instrument "Lab Unit M 20" with the plates and frames of the DDS firm at the temperature of 18 degrees C. Composite membranes of the types HR 95 PP and HR 98 PP (aromatic polyamide membrane HR 95 PP of 95% NaCl rejection and HR 98 PP of 97.5% NaCl rejection), with the total surface of 0.347 m(2), were applied. Research results showed that the mentioned processing parameters, molecular mass and molecule structure influenced the permeate flux during the model solution concentration. Better permeate flux was achieved in alcohol solution concentration with the membrane type HR 95 PP than with the HR 98 PP membrane. The membrane type HR 98 PP had greater permeability during the model solution concentration of esters and aldehydes. (c) 2006 Elsevier Ltd. All rights reserved.