aqueous solutions of polysaccharide biopolymers , e . g ., xanthomonas / carbohydrate fermentation worts , are heat treated for more than 5 , but less than 60 minutes , at a ph ranging from 3 . 5 to 6 . 2 , to improve the viscosifying , filterability and injectability properties thereof , and are well adapted , e . g ., for secondary and tertiary hydrocarbon recovery by waterflooding therewith .