In a few hours the mixture begins to bubble, the agitation increasing in violence with the continuous formation and escape of carbon-dioxide (carbonic acid gas). The fermentation produces two main factors, alcohol and carbon-dioxide—the former remains in the liquid, but the latter forces its way out.
The transformed liquid consists chiefly of crude alcohol and water, with numerous minor miscellaneous ingredients, and is known in distiller's parlance as "beer ;" but it is not a drinkable beverage.
The Sour Mash process requires more time for fermentation than the Sweet Mash and does not yield as high an alcoholic percentage, but it gives the product more of the grain flavor.
The fourth stage employs the universal principle of Distillation (which see) to separate the alcohol from a large part of the water, leaving also the solids and cer tain deleterious ingredients behind. The exact processes vary in different localities and establishments and with the grade of whisky manufactured—infinite pains being taken in the making of finer types, as by double and triple distillation and the use of innumerable chambered stills placed one on top of the other so as to resemble a "column"—but whatever the variations, the product carried over is "whisky," or can be made so by the addition of water to reduce it to potable strength.
Straight Whisky is stored in the distillery bonded warehouses; Blended Whisky in "free" warehouses.
The filled barrels of Straight Whisky remain in the warehouses under the control of government officers as long as the manufacturer or other owner desires, being sub ject to withdrawal at any time on payment of the government charges. The full "bonded" period is eight years, at the end of which time the payment of the tax is com pulsory.
Whisky as marketed generally contains about 50% alcohol by volume. The stand ard of alcoholic strength in spirituous liquors is termed Proof (which see). If less than 80° Proof, the degrees of Proof must be stated on the label.