The system gelatin-poly(acrylic acid) (PAA) undergoes not only complex coacervation but also flocculation. The latter is incompatible with an encapsulation process. pH adjustment rate, ionic strength, temperature, and total macromolecular concentration have been studied to understand the origin of flocculation and to obtain a set of optimized parameters for coacervation using on-line turbidimetric titration. State diagrams were built, by varying gelatin/PAA mass ratio (R) and pH, for different PAA molar mass, which gave occurrence conditions of flocculation and coacervation. Flocculation can be avoided without significant yield decrease by pH adjustment. On the other hand, a modification of ratio (R) affects both coacervation yield and coacervate phase concentration. Spectrophotometric titration reveals a relative independence of the effective ratio within the coacervate and the initial mixing ratio before reaction. Conclusions are made concerning the use of this couple in an encapsulation process. (c) 2006 Wiley Periodicals, Inc.