# Yeast Fermentation for Production of Neutral Distilled Spirits
## 2 Overview of Neutral Distilled Spirits Production
### Substrates and Wort Preparation for Fermentation
\begin{table}
\begin{tabular}{c c c} \hline
**Media** & **Fementable Sugars** & **Alcohol Product Examples** \\ \hline Starch hydrolyses (e.g., from maize, wheat) & Glucose & Grain neutral spirit \\ using amylolytic enzymes & & \\ \hline Barley malt wort & Glucose, maltose, maltotriose & Malt whisky \\ \hline Cereal wort based on barley malt plus un-malted & & Scotch grain whisky, Bourbon \\ starch from wheat, rye, maize, sorghum, etc. & Glucose, maltose, maltotriose & whiskey, grain neutral spirit (for gin, \\  & & vodka etc.) \\ \hline Rice hydrolysate (from Koji enzymes) & Glucose & Shochu, Awamori (Japan) \\ \hline Sorghum (and other grains) & Various, mainly glucose & Baijiu (China) \\ hydrolysates & & \\ \hline Potato hydrolysate using amylolytic enzymes & Glucose & Aquavit, vodka \\ \hline Coconut flower sap & Glucose, fructose & Arrack (Sri Lanka) \\ \hline Agave & &
\begin{tabular}{c} Tequila, mescal, bacanora, sotol \\ (Mexico) \\ \end{tabular} \\ \hline Sugar cane molasses & Sucrose & Rum \\ \hline Sugar beet molasses & Sucrose & Neutral spirit \\ \hline Sugar cane juice & Sucrose & Cachaca (Brazil), Rhum Agricole \\ \hline Grape must \& pomace, fruit juices & Glucose, fructose & Cognac, Armagnac, brandy, grappa, \\  & & & \\  & & & \\ \hline Cheese whey & Lactose & Gin, vodka, cream liqueurs \\ \hline \end{tabular}
\end{table} 
Table 2: Some fermentation media for the production of distilled spirits. (Adapted from [10]). respectively. The enzymes can further be applied to aid in the processability of the word. For example, a \(\beta\)-glucanase can be applied when high \(\beta\)-glucans concentrations could cause word run-off problems due to their high viscosity. Irrespective of the enzyme sources for cereal-word production, starch degradation processes do not stop when the word leaves the mashing vessel. This is because distiller's word is not boiled following mashing, as in beer production. Consequently, the residual malt or exogenous enzymes continue their amylolysis during fermentation, and this resembles the simultaneous saccharification and fermentation (SSF) processes typically found in bioethanol (fuel alcohol) distilleries that process maize and wheat [12]. Although cereals are the most common substrate utilised in the production of neutral spirits, likely due to being cost-effective products of local agriculture, some distillers use alternative, non-cereal sources of starch-based spirits. For example, potatoes can be used [13], but the basic steps of reducing particle size, starch gelatinisation, and mashing remain the same, including milling, cooking with alpha-amylase, cooling, and the addition of amyloglucidase prior to yeast fermentation. Following mashing and starch conversion, cooling the word to suitable temperatures (e.g., 20-30 \({}^{\circ}\)C) then takes place to facilitate active yeast fermentation. Selected distilling strains of _S. cerevisiae_ typically produce a fermented wash at 8-10% _v/v_ ethanol. An interesting raw material for neutral spirit production is cheese whey. This liquid is a by-product of the cheese-making process and is rich in lactose, as well as other nutrients, for yeast fermentation. Although _S. cerevisiae_ is unable to ferment lactose, other yeasts, notably _Kluyveromyces marxianus_, are able to do so, and this property has been exploited by several large-scale distillery operations worldwide (e.g., in Ireland, New Zealand, Turkey). See [PERSON] [14], [PERSON] and [PERSON] [15], and [PERSON] et al. [16] for further information on cheese-whey-based spirits.