PURPOSE: To automate the control of a machine, etc., according to detected moisture of tea leaves by measuring electrical conductivity of tea leaves with a sensor at regular intervals during a conductivity-determination period, comparing the measured conductivity with a preset target value and detecting the increase of moisture of tea leaves with time elapsed from the start of the measurement.

CONSTITUTION: A tea pressing plate 7 is lifted after measuring the electrical conductivity of sampled tea leaves a... using a moisture sensor S for a prescribed period. A side wall 5 for pushing is moved toward the front machine-side with an air cylinder 6 to return the measured tea leaves in a sample container box 1 into the tea-processing machine to complete a cycle of the sampling and measurement. The moisture of tea leaves measured by the sensor S as electric current increases with time from the start of the pressing with the press plate 7 within one cycle of the measurement. The moisture becomes an equilibrium state at a definite level. The rate of increase of the electric current is high in the case of wet tea leaves and decreases according to the progress of drying.