Distilled Spirits

The manufacturing of distilled spirits such as scotch, whiskey, and gin is initially similar to that of beer, except the wort is not boiled. Consequently, degradation of starch by the enzymes in the wort continues during the fermentation. When the fermentation is complete, the ethanol is purified by distillation.

Different types of spirits are made in different ways. For example, rum is made by fermenting sugar cane or molasses. Malt scotch whiskey is the product of the fermentation of barley that is then aged for several years in oak sherry casks. The wood and the residual sherry contribute both flavor and color to the whiskey as it ages. Lactic acid bacteria are used to produce lactic acid in grain mash for making sour-mash whiskey. The yeast S. cerevisiae subsequently ferments the sour mash to form alcohol. The distilled spirit tequila is traditionally made from the fermentation of juices from the agave plant using the bacterium Zymomonas mobilis. This bacterium ferments sugars to ethanol and CO2 via a pathway similar to the yeast alcoholic fermentation pathway.

The beer is ripened in the lagering tank. Yeast and unwanted flavor compounds settle out.

Beer is clarified by filtration, and pasteurized or membrane filtered before bottling.

Lagering tank firm

Filtration and bottling

Figure 32.5 Commercial Production of Beer What is the purpose of the membrane filtering in the last step?

The fermentation process generates beer with an alcohol content ranging from 3.4% to 6%. Most of the yeasts settle out following fermentation and are removed. These yeasts can be sold as flavor and dietary supplements. The beer is then aged, during which time residual unwanted flavor compounds are metabolized by remaining yeast cells or settle out. Cask-conditioned beer undergoes a second fermentation, which generates CO2 in the cask. Other beers must be carbonated to replace the CO2

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