
181Case Study: The Production of Nisin
at the bottom section of the foam layer increased from 0.011 to 0.029, due to
internal reux. There was no signicant difference in the top section of the
foam layer when the total foam height was varied, probably due to the fact
that the foam was already very dry and the foam drainage rate was very low.
A signicant enhancement in enrichment was not observed either. However,
one cannot say the same for larger columns with further increases in foam
height. Because the foam columns are scaled-up on the basis of a supercial
gas velocity, an increase in the absolute foam height increases the bubble
residence ...