Preservation of plant material by large scale sorption freeze‐drying

Abstract

A large-scale sealed system for freeze-drying herbage is described. It utilizes the principle of sorption drying and is dependent upon the vapour pressure differential (VPD) between the herbage and the silica gel drying agent. Ice sublimes to vapour from the sample in a system operating at approximately -10°C and the vapour is adsorbed by silica gel in an air stream recycled by a blower; equal masses (up to 50 kg each) of wet herbage and silica gel are used. The system is simple to construct and is relatively inexpensive.Approximately eight days drying time are needed to reduce moisture content from 90 to 10%. Twenty-four different species or cultivars of both temperate and tropical grasses and legumes sampled at several stages of maturity have been dried in the system. When snap-frozen herbage is freeze-dried by this process the physical and chemical changes that otherwise occur when herbage is harvested and prepared for evaluation can be reduced and sufficient material can be obtained to permit animal feeding studies as well as chemical analyses.