Cake appearance of freeze-dried products

While there is no regulatory requirement for appearance, one expects to see an “elegant” cake, i.e., one that is uniform, white to off-white and does not show any sign of cracking or appreciable shrinkage or collapse). Nevertheless, there are several conditions when product failure is quite clear from a simple visual assessment of the cake appearance. This publication provides pictures of vials with example defects in the freeze-dried cake along with a table that explains our various defects can result as a consequence of the product formulation of the process design. Corrective actions to address these are also provided.