Inspissation is the process of thickening by dehydration. Inspissation is the process of thickening by dehydration. Inspissation is the process used when heating high-protein containing media; for example to enable recovery of bacteria for testing. Once inspissation has occurred, any stained bacteria, such as Mycobacteria, can then be isolated. A Serum inspissation or Fractional sterilization is a process of heating an article on 3 successive days as follows: In cystic fibrosis, inspissation of secretions in the respiratory and gastrointestinal tracts is a major mechanism of causing the disease.