SHORT-TIME DRYING OF HEAT-SENSITIVE, BIOLOGICALLY-ACTIVE PULPS AND PASTES

Tomato concentrate and baker's yeast suspension were dried in the labo ratory scale Mechanically Spouted Bed dryer with inert packing. Due to a large contact surface Provided by the inert particles, very fast dr ying process can be achieved, if the thickness of the wet coating form ed on the surface of the inert packing is film-like. The diffusion res istance can be then considered negligible and drying can be performed at ''quasi-constant'' rate. Derived from hydrodynamic characteristics the contact time between hot air and the wet coating is very short, th erefore gentle drying process can be performed. The quality of the dri ed yeast was controlled by counting the living cells (relative viabili ty) and by measurement of the dough rise time. During continuous dryin g of thermoplastic tomato puree the ''case hardening'' periods could b e shortened and tomato powder with insignificant quality loss was prod uced.