Abstract: A composting machine, particularly for vermicompost, is elongated in shape. Grates with openings are laid into a frame of the machine, onto cross beams which correctly locate the grates to be closely adjacent to one another except along a longitudinal center line of the machine, where the spaced-apart grates form a guiding channel through the length of the machine. Within this travels a downwardly extending keel of a carriage that is moved through the length of the machine when a bottom layer of finished compost is to be harvested from the bottom of the mass of compost material. To the carriage is attached a cutting blade extending the width of the machine, driven by longitudinal tension lines under the control of a driving motor. A tensioner maintains tension in the cable.