Notes on the Freeze-Drying of Plant Tissue

The moving-air type of freeze-dry apparatus decreases the length of time needed to dehydrate plant material but is detrimental to easily oxidizable compounds. Changes are described in the apparatus that both improve and simplify the original design. They consist of: (1) using high purity nitrogen instead of air thus preventing the oxidizing of compounds and allowing for the removal of the condenser necessary to dry the incoming air; (2) modification of the top of the dehydration chamber so that die tissue can be drawn from the bottom and warmed to room temperature before being removed from the apparatus; and (3) a new design for the tissue containers permitting the tissue to be more securely held and easily manipulated. Various freezing mixtures and infiltration procedures and materials were tried and the results described. A theory is proposed to explain the effectiveness of the moving-gas type apparatus based on the ability of the gas to maintain material at the optimal temperature while sweeping the water molecules from the surface.