The aqueous growth medium used to support the growth of a microbiological culture in a bioreactor. Also known as a culture medium or growth medium, it contains all the necessary nutrients to sustain growth. The broth in a bioreactor is first inoculated with a sample of living microorganism, which then multiply consuming the nutrients. The rate of growth of the microbial cells can be determined by measuring the turbidity of the broth or taking samples and determining the cell dry weight.