Evaluation of fluidized versus spouted bed drying of baker's yeast

Drying of baker's yeast (Saccharomyces cerevisiae) was examined experimentally in laboratory scale fluidized bed and spouted bed dryers. Pressed yeast samples (70% moisture content, wb) were prepared in granular form (0.8-1 mm diameter) and dried first in a fluidized bed to characterize their fluidization and drying properties. It was observed that high moisture yeast particles (up to 35%, wb) belong to group C and D of Geldart's classification, especially for higher (>200 mm) bed heights making their fluidization very difficult. On the other hand, fluidization of pre-dried yeast particles with moisture content under 35%, wb (group B) was very easy. This characterization suggests a new concept for drying of baker's yeast i.e. spouted bed drying in the first stage and fluidized bed in the second stage or spouted bed drying for the entire process. The quality parameter examined during the drying process was viability of yeast cells at a standard moisture content (6-8%, wb).