Preliminary Investigation Into the Use of a Dehumidifying for Drying Wild Herbal Teas in Southeast Alaska

Abstract

This project investigates the use of a dehumidifying dry kiln (traditionally used for drying lumber) for drying wild herbal teas in Southeast Alaska. Its major considerations are kiln design, moisture content data (for use in drying schedules), and preliminary drying schedules. Project conclusions result from literature review and experimentation. Regarding kiln design for uniformity and efficiency, the researcher found the following principles of utmost importance: 1) proper direction of airflow (achieved by incorporating measures that will direct the airflow, such as baffling and air deflectors); 2) maximizing space by fitting the maximum number of drying racks into the kiln and using a small spacing (9cm) between drying trays; and 3) minimizing electric costs by installing a heat source other than electric auxiliary heat, as well as operating the kiln continuously until materials are dry. Regarding moisture content (MC), the research found that herbal teas should be dried to 5-10 percent MC (green basis), and that the moisture contents of most green materials collected in Haines were too variable to use for creating drying schedules. Regarding drying schedules, the research found that pre-drying plant materials in ambient air for about a day improves quality and efficiency of the kiln drying process. Material depth for some materials, including dandelion and fireweed leaf. The main problem identified was the variation in drying rates between different leaf parts (leaf blades dried out much faster than midveins and became brittle). This problem could be avoided in the future by using water sorption isotherm data to ensure that no part of any material will dry out below a given MC. It is still unclear whether a dehumidifying kiln is an economically viable option for drying wild herbs.