Abstract: A monitoring system for a bioreactor is disclosed. The monitoring system includes a cuvette arranged to receive a fluid from a bioreactor, wherein the fluid includes a portion of a biomass. The system further includes a light source arranged to project light, at wavelengths absorbable by the biomass, into the cuvette. A sensor is arranged to detect portions of the light that are not absorbed by the biomass. The system further includes a controller coupled to receive an indication of an amount of light detected by the sensor. The indication of the amount of detected light is usable to determine an amount of biomass in the cuvette.