This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
If the fruit juices are allowed to ferment, the aroma is more delicate, and the product of a much better bouquet. After the fruits are crushed, put the mass in wooden tanks or in demijohns or earthenware vessels, add about two to four per cent, of sugar, mix, cover the vessel, and let ferment for three to four days. Stir the mass a few times while fermenting. As this process is going on in summer time, the temperature is favorable for fermentation. The latter produces alcohol and acts in connection with the free organic acid present as a solvent upon the coloring matter of the fruits, thus producing a more intensely colored juice. The alcohol also causes the separation of the pectines and salts, and the consequence is that the juice loses its mucilaginous consistency, becomes a thin liquid, is more readily and completely pressed out, and will also become perfectly clear when at rest. The small addition of sugar becomes invert-sugar, and passes through the fermentation too. The alcohol also forms ethers, especially acetic ether, and the juice therefore assumes a very agreeable and aromatic odor and taste. For immediate use, filter through filtering bag.
Although the fermented juice, when properly prepared and kept, will keep an indefinite time, as a means of precaution, and to check a possible secondary fermentation, a preservative, such as salicylic acid, about two ounces to twenty-five gallons of juice, or ten grains to a quart, may be added, or, what is still better, ten per cent, of alcohol of 95°, which brings the alcoholic strength of the juice to about fifteen per cent., and this will act as a sure preservative, since alcohol if present in the amount of more than ten per cent, will not permit fermentation. When these fermented fruit juices are used for flavoring syrups, no addition of an ether or artificial fruit essence is necessary, as they contain the full aroma.
Adulterated or imitated fruit juices are colored with fuchsine. To detect it Pusher proposes to soak a woolen or silk thread. A coloration caused from natural fruit juice is washed out by rinsing In water; if fuchsine was used, the thread remains red permanently.