The physical state of the product changes
from liquid as it passes through the drier from solution
to syrup and ®nally to solid form. Based on the report
published by Bellows and King (1973) and Downton et
al. (1982), if the viscosity of the product is below a
critical level of 107 Pa s, it may stay as syrup even at low
moisture levels. Depending upon the product characteristics
and composition, and drying conditions, the
surface of the drying droplets may remain plastic, re-
sulting in sticking on the drier wall or among themselves.
The amorphous product obtained at the end of
the drying process could, therefore, be either syrup, a
sticky powder or a relatively free-¯owing powder.