In the case of multiple or repeated batch fermentation,
the use of flocculating yeast strains plays an important role.
In this process, after starting a conventional batch, the
yeasts are decanted in the same vessel where they were cultivated
by removing the clarified culture broth. Then, an
equal amount of fresh culture medium is added for the following
batch. In this way, high cell concentrations are
reached and inhibition effect by ethanol is reduced without
the need of adding flocculation aids or using separation or
recirculation devices. These repeated batches can be carried
out until the moment when the activity and viability of culture
is lost as a consequence of a high exposition to the fermentation
environment. When this occurs, the system
should be re-inoculated. Some examples of typical batch,
fed-batch and repeated batch fermentations for bioethanol
production from sugar cane molasses can be observed in
Table 3.