Method of concentrating natural fruit juices by reverse osmosis

Abstract

A reverse osmosis method of concentrating fruit juices wherein a major portion of the fruit juice sugars are removed in a reverse osmosis first stage from the fruit juice at about room temperature and a pressure in the range 500 to 1500 psi, using porous cellulose acetate membrane material, while flavor compounds are removed in a reverse osmosis second stage from the separated water in liquid form therefrom at a temperature in the range 0.degree. C. to about room temperature and a pressure substantially in the range 50 to 1000 psi using asymmetric, porous, polymeric membrane material which is non-polar relative to the membrane material of the first stage as determined by .delta..sub.d of the solubility parameter of the membrane materials. The membrane material of the second stage is preferably at least as polar as the membrane material of the first stage and is preferably of a material selected from the group consisting of cellulose acetate propionate, cellulose acetate butyrate, ethyl cellulose, aromatic polyamide, aromatic polyhydrazide and aromatic polyamide-polyhydrazide copolymer. Preferably the fruit juice fed to the first stage is at a temperature in the range 15.degree. to 30.degree. C. and the separated water fed to the second stage is at a temperature in the range 5.degree. to 10.degree. C.