1. Introduction

Whey processing is a mature manufacturing sector. More than 75 years have passed since multiple effect evaporators and spray dryers were developed and applied to whey processing [1]. Nevertheless, the technology continues to evolve. The initial processes focused on removing water and concentrating all solids-non-fat into dry powders. Today, membranes, ion exchange resins, and chromatography are some of the new unit operations routinely applied in the processing of an increasingly diverse assortment of powders originating from whey.

This development has greatly benefitted larger cheese producers as these powders generally provide significant revenue potential. Unfortunately, smaller scale cheese processors are rarely able to benefit from these products. Whey powder facilities are expensive to construct and are therefore not an option for smaller cheese companies.

Large-scale cheese makers in the US typically only produce one type of cheese such as cheddar or mozzarella. This leads to production of large volumes of sweet whey streams with consistent composition that are well suited for current whey manufacturing facilities. In contrast, smaller specialty cheese producers tend to produce multiple different cheese types and must deal with different whey streams. While most hard renneted cheeses produce relatively similar whey streams, the lactic cheeses such as cottage or cream cheese along with Greek yogurt create acid whey. Acid whey primarily differs from sweet whey in mineral and acid content. Specifically, acid whey may have twice the calcium content and more than 10 times the lactic acid content as compared to sweet whey. The high levels of lactic acid interfere with the drying process as it contributes to forming sticky powder

agglomerates within dryers. Consequently, acid whey cannot be easily processed into whey powders.

Giving these limitations, small-scale cheese processors and acid whey producers have limited options for whey disposal. At best, they aim to dispose of whey without a cost. This could involve using whey as an animal feed source, land application, or disposal in farm lagoons. All of these options have potential negative consequences. Dragone et al. suggested that 47% of whey produced in Portugal (mostly from small scale producers) was disposed through land application or directly into streams [2]. The environmental consequences of this can be significant due to the high Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) of whey, which are 40–60 and 50–80 g/L respectively [3]. This leads to depletion of dissolved oxygen when disposed into lakes and streams. Whey does not appear to negatively impact the flavor of beef from cattle fed whey [4, 5], although some negative impacts such as acidosis and diminished carcass grade have been noted [6]. In addition, feeding whey back to the livestock at a farmstead creamery will likely increase the risk of phage development.

Nevertheless, self-disposal may be favorable compared to paying for disposal through municipal wastewater treatment systems or paying others to haul the whey away for disposal. Rates for disposal of waste through municipal water/waste treatment rates are based upon the mass of BOD being removed at the treatment facility thereby making it an expensive waste treatment option for whey. In fact, it may not even be an option as some municipalities refuse to treat whey. A recent (2015) unpublished survey of specialty cheesemakers in the US revealed that most of the very small artisan cheese makers manage to dispose of whey at no cost through feeding to own or local neighborhood animals. However, as soon as cheese production increases above 5000 kg/year, most are obliged to pay for disposal at rates up to \$105/1000 kg of whey. This demonstrates that whey disposal can be a significant expense for medium scale cheese processors that are too small to produce whey powders and too large to dispose of whey through feeding or other small-scale disposal. As profit margins for small-scale cheese makers are tight [7], whey disposal costs can significantly impact business sustainability.

Due to these challenges, small-scale whey producers are continuously looking for whey disposal options. The fermentation and distillation of whey can be done to produce bioethanol or a potable spirit. The fermentation and distillation of whey to produce potable spirits may be a potential value-added option for small scale cheese makers. Not only does this allow for concentrating the initial whey stream, but it also enables the production of an additional high-priced product. For example, if a 750 ml bottle of vodka sells for \$30 that would translate to approximately \$1–1.5 per L of initial whey. This could potentially create as much revenue as the corresponding cheese.
