9. Distillation

Once the whey sugars, primarily lactose and its monosaccharide constituents galactose and glucose, have been converted into ethanol, there is a need to concentrate the alcohol up to a strength that is appropriate for a spirituous product. Broadly speaking the ethanol yield from a whey fermentation will be typically 2–5% v/v, depending on the fermentation procedures and any preconcentration applied. The fermented feed though can contain significant levels of other whey constituents such as calcium salts and proteins. Depending on the process design, the whey may be pretreated to remove proteins and salts.

The requirements of the distillation operation are straight-forward, at least in principle. The fermented whey is to a first approximation a dilute solution of ethanol in water, and this ethanol needs to be concentrated by around an order of magnitude to generate the basis of an alcoholic spirit. However, other volatile components present, either from the parent whey or produced during fermentation as secondary metabolites, also termed congeners. Whilst these compounds are present in relatively low concentrations they can contribute to the flavor of the distilled spirit and the distiller needs to make a decision as to how much of these flavors should be retained in the resulting spirit.

### Whey to Vodka DOI: http://dx.doi.org/10.5772/intechopen.81679

In any case, the distillation process consists of three distinct activities: heating, to create vapor from the still feed, condensation, to convert vapor into the liquid spirit, and collection of the spirit. Each of these activities can be achieved using equipment of widely varying complexity and broadly speaking the higher the purity of the alcohol the more complex the equipment needs to be. For the distillation of fermented whey the common primary aim is to create "neutral alcohol" (i.e. alcohol that has no extraneous color or flavor) and so both the concentration of ethanol and removal of flavor-active components is usually required. To achieve this the ratio of surface area to volume in the still is a key design consideration. Generally, the introduction of more surface area tends to enhance the separation of ethanol and congeners, resulting in a cleaner, more neutral spirit. With the rapid development of the craft spirits industry, especially since the turn of the century, there has been a plethora of new still designs and fabricators available to the nascent distiller. To remove any congeners present is usually achieved by multiple distillations, the introduction of "plates" into a still or both.

Whilst the distilled spirit is the primary product from distillation, it is a relatively minor proportion of the still output. If the alcohol is around 3% v/v and the output is, say, 70% v/v, then the spirit fraction is only about 5% of the total feed volume, with the remaining 95% as "waste". However the removal of BOD (mainly present in whey as lactose) and the distillation of ethanol from the fermented whey, means that the BOD is substantially reduced, which in turn reduces effluent costs. If protein is removed prior to distillation and utilized elsewhere, then the resulting still waste stream is amenable to further treatment, for instance by anaerobic digestion. In any case, the distillation operation results in a significant waste stream in itself that must be considered in any process design.

The scale of the fermentation and distillation facilities is straight-forward to estimate. For a cheese plant that produces 5000 kg cheese per year, around 45,000 l of whey will be produced. On a weekly basis this is around 100 kg of cheese and 900 l of whey. If the lactose content is 5% w/v and the sugars are completely fermented (for instance using yeasts such as K. marxianus), the ethanol yield will be up to around 3% v/v. Allowing 5 days for a fermentation to complete, two fermenters of 1000 l will be required, and a still of 300–1000 l capacity. The exact capacity depends on how often the distilling operation is performed per week.
