8. Industrial whey fermentation process and technology for potable spirits

The fermentation process and technology used for the Carbery process are identical for potable spirits and bioethanol production [8, 9]. The Carbery process (Figure 5) is used for the industrial conversion of whey to potable spirits. Differences in the process occur during the distillation and during post-distillation processing. Whey/whey permeate is received at the facility and must be cooled to the specified fermentation temperature. Once cooled, the whey is pumped into fermentation tanks and inoculated with K. marxianus. The common inoculation rate for commercial spirit production is <sup>1</sup>–<sup>5</sup> ˜ 107 cells/ml [61]. K. marxianus is grown in yeast propagation vessels referred to as "Donas". These yeast propagation vessels are aerobic and pumped with filtered air to promote yeast growth. This allows yeast to be maintained in growth phase which increases their ability to produce alcohol and reduces lag time when inoculated in whey [61]. The fermentation tanks are cylindroconical vessels jacketed with ethylene glycol or other coolant for temperature control. The quantity and size of the fermentation tanks vary based upon the production facility capacity. Compressed air is used for agitation during

fermentation. The fermenting whey is pumped from vessel to vessel with monitoring of the specific gravity occurring throughout the process. The specific gravity of whey starts at approximately 1.022 g/cm<sup>3</sup> and drops to 1.008 g/cm<sup>3</sup> during fermentation. This drop in specific gravity is due the lactose within whey being converted to ethanol and CO2. The specific gravity measurement is used to determine the process flow rate. Fermentation time ranges between 12 and 24 h [8, 9]. Once the designated specific gravity has been reached, the fermented whey is separated from the yeast via gravity (yeast falling out of solution) and/or through separation technology, such as centrifugation. The yeast can potentially be recycled for later batches or further processed for human or animal consumption. The fermented whey, now called a "beer" is held in a holding tank until distillation [8, 9].
