In order to prevent materials as mentioned above from denaturation by heat
, it has been thought of to lower the vaporization temperature of the water contained therein, and thus a vacuum drying process has been employed.
Such a process has been usually carried out by passing a belt through a vacuum dryer. A degree of vacuum in the range of 1 to 100 Torr has been employed although it varies depending on the materials.
As what is to be particularly stressed in this case, the state of the materials distributed on the belt is mentioned. Namely, materials should be supplied onto the belt continuously, in a definite amount and in a uniform thickness. If thissupplying state fluctuates, the balance between the materials and the heat quantity supplied is destroyed, resulting in heat denaturation of the materials or inferior dried products having an uneven water content.