Mikkel Nordkvist

Scale-down/scale-up studies leading to improved commercial beer fermentation.

Scale‐up/scale‐down techniques are vital for successful and safe commercial‐scale bioprocess design and operation. An example is given in this review of recent studies related to beer production. Work at the bench scale shows that brewing yeast is not compromised by mechanical agitation up to 4.5 W/kg; and that compared with fermentations mixed by CO2 evolution, agitation ≥ 0.04 W/kg is able to reduce fermentation time by about 20%. Work at the commercial scale in cylindroconical fermenters shows that, without mechanical agitation, most of the yeast sediments into the cone for about 50% of the fermentation time, leading to poor temperature control. Stirrer mixing overcomes these problems and leads to a similar reduction in batch time as the bench‐scale tests and greatly reduces its variability, but is difficult to install in extant fermenters. The mixing characteristics of a new jet mixer, a rotary jet mixer, which overcomes these difficulties, are reported, based on pilot‐scale studies. This change enables the advantages of stirring to be achieved at the commercial scale without the problems. In addition, more of the fermentable sugars are converted into ethanol. This review shows the effectiveness of scale‐up/scale‐down studies for improving commercial operations. Suggestions for further studies are made: one concerning the impact of homogenization on the removal of vicinal diketones and the other on the location of bubble formation at the commercial scale.