The hardness of an ice layer formed on the inner wall of a crystallizer for freeze concentration has been investigated on the basis of the torque required for scraping the layer. A torque increase observed in first scraping the ice layer growing from the wall decreased with increasing rotational speed and the concentration of solute in ice. After that, variations of the torque required for consecutive scraping were classified into two patterns. In scraping the ice layer formed in water and cephalosporin c sodium solution, the torque increased gradually with time, and finally scraping became impossible. On the other hand, the torque hardly changes with time for sodium chloride, glucose and isopropyl alcohol aqueous solutions, and the ice layer was readily scraped. These findings show that ice layers formed are hard in the former solutions but soft in the latter solutions. However, it has been confirmed that the ice layer formed in cephalosporin c sodium solution changes from a hard state to a soft one by adding isopropyl alcohol to the solution. The properties of the ice layer are investigated by microphotograph observation and DSC measurement. The results suggest that the hardness of the ice layer depends on the composition of the frozen body.