Limitations of shake-flask culture

As outlined above the main limitation of batch culture is the difficult balance which must be struck among the space available to incubate Erlenmeyer flasks and the oxygen mass transfer rate.  In addition batch culture should not be regarded as solutions of defined composition. Before  the  Bacteria are  introduced into  the  medium it may  be  possible to define all the  components of the  medium even  in exact  terms of the  elemental concentration of nitrogen, carbon, phosphorus, sulfur and many more. As soon as the organism starts to grow the composition of the medium change and will continue to change until the organism stops growing. We assume that biomass increases and the carbon and energy sources decrease in a regular manner. However, microorganisms secrete a variety of small molecules into the medium as they grow from protons to heterocyclic carbon compounds. Thus  during batch culture the  pH as well as the  concentrations of oxygen and many other compounds not only change but can fluctuate in an unpredictable manner.  To reduce the effect of pH fluctuations the growth medium is buffered normally with a phosphate buffer, but even so a change of one or more units of pH during batch culture is not uncommon. The onset of stationary phase is taken to be due to the lack of a suitable carbon source but is frequently the result of the accumulation of toxic metabolites in batch culture. Despite these limitations batch culture is a simple, quick and for the most part reproducible techniques of growing small quantities of micro- organisms in liquid culture