In the process of freeze concentration (FC), the main problems in operating the counter-current wash column used for separating ice from ice slurries are channeling and viscous fingering. These phenomena lead to the mixing of pure water and mother liquid, as well as entrainment of mother liquid within the removed ice. Experimental and thermal analysis of the wash front interface in this research relates ice melting and wash front breakthrough with the operating conditions (such as the wash water temperature, ice bed temperature and porosity). Criteria for wash front stability are proposed. (C) 2009 American Institute of Chemical Engineers AIChE. J, 55: 2835-2847, 2009