Electricity consumption of drying and the effect of the dryer and temperature on the chemical quality of nettle leaves (Urtica dioica L.), birch leaves (Betula pendula, Betula pubescens) and roseroot (Rhodiola rosea L.)

Drying can constitute the majority of the energy costs and thus, manufacturing costs, in plant refining. The use of higher drying temperatures accelerates drying and reduces total electricity consumption. However, higher drying temperatures can also reduce the chemical quality of plants, as heat sensitive compounds can degrade or evaporate. The purpose of the study was to find the optimum drying temperature for nettle leaves (Urtica dioica L.), white and silver birch leaves (Betula pubescens, Betula pendula) and roseroot (Rhodiola rosea L.) in terms of electricity consumption and quality. Selected plants were dried with drying oven, convective dryer and vacuum dryer between 40 and 80 °C. The quality was determined by measuring total polyphenol content, antioxidant capacity and active compounds of roseroot. The lowest total electricity consumption was obtained by drying oven, but the highest chemical quality was obtained by vacuum dryer. The optimum drying temperature varied between 65 and 80 °C.