Temperature control in solid substrate fermentation through discontinuous rotation

A laboratory-scale system for controlled dynamic solid substrate fermentation was developed and tested. The fermentation takes place in a stainless steel discontinuously rotating drum reactor, under controlled conditions of temperature, gas composition, relative humidity and direction and rate of rotation. The system was tested on a model fermentation of soya beans with Rhizopus oligosporus. In contrast to the traditional tempe fermentation, a granular product is obtained and build-up of heat and mass gradients is restricted. Despite the discontinuous rotation, the fungal growth continues, as evidenced by the production of heat. The rate of cooling depends on the temperature of the gas flushed through the reactor, the gas flow rate and the lenght of the rotation period. As a consequence of the homogeneous temperature control, the fungal heat development continued up to 70 h of fermentation. This is in clear contrast with the traditional tempe fermentation, which is already limited after 36 h by its own heat accumulation.