Thermostability of thin juice

The initial thin juice pH value usually changes during juice evaporation. As long as the pH value of the final thick juice differs maximal ±0.5 pH units, preferably ±0.2 pH units, from that of thin juice, the thin juice is considered thermostable. The observed change of the juice pH value depends on the ratio between dissolved ammonia and carbon dioxide in thin juice. During the juice concentration both volatile components will evaporate at which they have opposite effects with respect to the pH value change. Ammonia is dissolved as ammonium ion in the juice and leaves a proton in the juice upon evaporation, whereas carbon dioxide is dissolved mainly as bicarbonate and delivers alkali upon evaporation. This paper explains why a thermostable thin juice is crucial for the effectiveness of the following process steps evaporation and crystallization. Details about the origin of ammonia and carbon dioxide will be presented, as well as possible ways to control the thin juice thermostability by influencing the ammonia to carbon dioxide ratio.