13. Product quality

Spirit quality can be influenced by several factors including source of the whey, fermentation parameters, still configuration and post- distillation product treatment. Congeners, minor volatile constituents of a spirit influence it's the organoleptic qualities. The perception of congeners is considered a flaw in vodka. Congeners are present in raw whey and are formed as secondary metabolites during the fermentation process. Congeners within whey can be carried over during the distillation process and are similar to congeners in other spirits [2].

The source of whey and fermentation parameters can influence the composition of congeners in fermented whey. The composition of the volatile aroma compounds within milk and other dairy products can vary depending upon the source of the milk [62]. The milk producer's diet and geographic location can be attributed to the presence volatile compounds such as terpenes and terpenoids [63, 64]. The cheese production process can also influence volatile compound composition of whey, particularly the application of heat and exposure to microorganisms. Exposure to heat can create thermal artifacts and influence chemical reaction rates within whey. The exposure of milk or whey to microbes can influence the volatile compounds

present in whey. The metabolites produced by microbes can include alcohols aldehydes, esters and ketones, all which can influence organoleptic quality. The microbial populations can differ per facility and geographic location [62]. Each cheese production facility can potentially produce wheys with different volatile compound compositions. The source of whey can influence the composition of volatile compounds present in a spirit [11].

Fermentation conditions can influence the production of secondary metabolites of K. marxianus [65, 66]. Traditional industrial ethanol production facilities take a laissez faire approach to fermentation conditions related to congeners production. These facilities' chief concern is maximizing ethanol production. A similar approach is taken at industrial whey to ethanol production facilities. The extractive distillation process is used to separate ethanol from congeners and produce a neutral spirit. It should be noted that congeners with a similar volatility as ethanol may be more difficult to separate. Diacetyl is difficult to remove via extractive distillation and can impart rancid butter or butterscotch aromas to a spirit [67]. Spirit quality is influenced by the number of plates used to separate the ethanol from the other volatile compounds. A greater number of plates allow for greater separation volatiles reducing the presence of congeners within the final spirit. The use of copper plates or other components which have contact with the spirit during the distillation process can influence the organoleptic qualities of the final product. Copper contact during distillation reduces sulfur aromas in spirits and can reduce concentration of sulfur containing compounds in the final spirit [68]. Post- distillation of filtration of the spirit can reduce the presence of congeners in the final product. Filtration with activated carbon can reduce the congeners in spirits and which can have a perceivable impact on the organoleptic qualities of the spirit [69].

If the spirit is to be sold as a vodka it should have a clean taste with no perceivable aroma. These requirements may not be as stringent if the product is to be sold as flavored spirit or mixed with other ingredients to produce a beverage such as Irish cream. Flavorings may mask presence of congeners or congeners with positive organoleptic qualities may enhance the final product.

For cheese makers with no prior knowledge of distillation, this entire process may appear intimidating. Fortunately, assistance is available for people entering into the distillation business [70].

### 14. Environmental implications of whey spirit production

The production of potable spirits from whey has the potential to reduce environmental impacts of cheese and spirit production [71]. The fermentation process reduces the environmental impact of whey. The conversion of lactose to CO2 and ethanol can reduce the BOD of whey by 75% [43] and aerobic cultivation can reduce BOD levels up to 95% [35]. The volume reduction during distillation and reduction of BOD during fermentation indicate that processing spent wash would be less economically and environmentally impactful than raw whey. K. marxianus is classified as GRAS and can be used as feed for livestock. It has also illustrated that production of a spirit from whey destined to be land spread instead of a similar grain-based spirit can reduce net CO2-equivalent emissions [71]. This 2018 study also indicated that the production of a wheybased spirit required less water than a grain-based spirit [71]. These factors indicate that the production of a spirit from whey may be beneficial to the whey producer, distiller and the environment.
