Method of concentrating natural fruit juices by reverse osmosis

A method of concentrating natural fruit juices by reverse osmosis, comprising:

• (a) in a first stage, passing a stream of the fruit juice substantially at room temperature and at a pressure in the range 500 to 1500 psi to a relatively higher pressure side of at least one porous, cellulose acetate, reverse osmosis membrane to retain, by reverse osmosis, a major portion of sugars of the fruit juice in the form of a syrup on the relatively higher pressure side, while causing the passage of separated water of the fruit juice containing flavor compounds of the fruit juice, through the said at least one membrane to a relatively lower pressure side thereof, said at least one cellulose acetate, reverse osmosis membrane having values for the solubility parameter due to hydrogen bonding (.delta..sub.h) and the solubility parameter due to dispersion (.delta..sub.d) of the orders of 6.33 cal.sup.1/2 cm.sup.-3/2 and 7.60 cal.sup.1/2 cm .sup.-3/2 respectively, and
• (b) in a second stage, passing a stream of the said separated water in liquid form, at a temperature in the range 0.degree. C. to the said temperature which is substantially at room temperature, and at a pressure substantially in the range 50 to 1000 psi, to a relatively higher pressure side of at least one asymmetric, porous, polymeric, reverse osmosis membrane in the path of the stream, which is non-polar relative to the said at least one porous, cellulose acetate, reverse osmosis membrane to retain, by reverse osmosis, flavor compounds of the fruit juice on the relatively higher pressure side while causing the passage of water therefrom through the said at least one second membrane to a relatively lower pressure side thereof, said at least one asymmeric, porous, polymeric, reverse osmosis membrane having a value for the said .delta..sub.d greater than 7.60 cal.sup.1/2 cm.sup.-3/2, and
• (c) collecting the retained sugars and flavor compounds of the fruit juice.