Mixing Scale-Down Studies for the Scale-Up of Beer Fermentation

Beer fermentations have traditionally been undertaken without the use of mechanical agitation with mixing being provided only by the CO2 evolved during the batch process. This approach has largely been maintained because of the belief in industry that rotating agitators would damage the yeast. In this work at the bench scale, we show that yeast is very robust and is able to withstand very intense agitation intensity under aerobic conditions without observable damage as measured by flow cytometry and other parameters. Much less intense agitation is also shown to reduce batch fermentation time for anaerobic beer production by about 25% compared to mixing by CO2 evolution. It is also shown that spatial variations in yeast concentration and temperature that exist when mixing by CO2 leads to slower fermentations and lower productivity. These bench scale studies have recently been supported by the work of others at the commercial scale from mixing by an impeller or by a rotary jet head (RJH). It is suggested that this situation is another where the myth of 'shear damage' has had a detrimental effect on the optimal operation of commercial bioprocessing.&'